-------
c»
3.0
O
1 2.0
cn
o
CD
o
o
CO
c.
o
1.0
O
cc
Q
0
CB
• I
-i r
QR = 0.23+2.57 X
r\ »
i i
0.2
0.4 0.6 0.8
Air-exchange rate (h )
1.0
1.2
XBL 818-1148
Figure 4
-------
3.0
^
o
CD
1 2.0
cn
o
CD
O
13
O
CO
o
o
o:
1.0
0
0
Roch 6
0.2
•QR =0.21+1.09 X
0.4
0.6
0.8
1.0
1.2
Figure 5
Air-exchange rate (h )
XBL 818-1147
-------
1.4-
1.2-
_cu 1.0
"o
CD
g1
o
o
0.8
-------
1.6
1.4
1.2
1.0
0.8
® 0.6
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0.2
0
-^ 2.5
o
O)
D
O
-8
1.5
CD
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0
AM-I
4/16/81
Air-exchange rate
Wind speed
4/17
J L
14
12
10 Q.
8
6
4
2
0
4/18
Time
4/19
4/20
Figure 7
121
-------
1.6
1.4
1.2
o> 1.0
"a
CD
CD
6
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X
O)
I
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_L
4/22
4/23
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Figure 8
122
-------
Table 1. Data from 101-House Survey of Radon Concentrat.on and Air-Exchange Rate
Sample
U.S. Energy-0
Efficient
Residences
San Francisco
Bay Area
Maryland '
Total
Monitoring Period
May- August
1979
July-September
1979
May-October
1980
No. of
Houses
16
29
56
101
Radon (pCi/1)
GMa GSDb
2.6 2.2
0.4 2.2
1.8 4.0
1.2 4.0
Air-Exchange
Rate (IT1)
GMa GSDb
0.23 2.2
0.28 2.5
0.35 2.2
0.31 2.3
Source Magnitude
(pCi I'1 h'1)
GMa GSDb
0.61 2.5
0.10 2.5
0.62 3.4
0.37 4.0
InX.]
GSD = exp
I [In X - ln(GM)]'
i=l 1
(N-l)
Source: Hollowell, C.D., Berk, J.V., Boegel, M.L., Ingersoll, J.G., Krinkel, D.L.,
and Nazaroff, W.W., 1980, Radon in Energy-Efficient Residences. Lawrence
Berkeley Laboratory Report LBL-9560, Berkeley, CA.
dSource: Berk, J.V., Boegel, M.L., Ingersoll, J.G., Nazaroff, W.W., Stitt, B.D. ,
and Zapalac, G.H., 1979, "Radon Measurements and Emanation Studies," in
Energy Efficient Buildings Program: chapter from the Energy and Environ-
ment Division Annual Report 1979, Lawrence Berkeley Laboratory Report
LBL-10704, Berkeley, CA.
6Source: Moschandreas, D.J., Rector, H.E., and Tierney, P.O., 1981, A Survey Study
of Residential Radon Levels, Geomet Technologies Report ES-877, Rockville,
MD.
In six of these 56 houses, the radon concentration was found to be less than the
detection limit of the measurement procedure (0.4 pCi/1 with 50% relative standard
deviation). For these houses the radon concentration was assumed to be 0.1 pCi/1
for purposes of calculating the geometric mean radon concentration and source
magnitude.
123
-------
Table 2. Summary of Radon Source Magnitude Measurements
for Six Houses Monitored Over Time
o
House Monitoring No. of Radon
ID Location Period Meas. (pCi/1)
b
CB N.J.
b
ROCH 6 N.Y.
b
ROCH 49 N.Y.
ROCH 60°' N.Y.
d
AM-1 MD.
d
SG-1 MD.
11/16-
12/17/80
1/8-
1/22/81
2/6-
2/20/81
4/16
4/20/81
4/16-
4/20/81
4/21-
4/23/81
36
25
11
32
28
18
3.2
(0.7-5.1)
1.6
(0.8-2.2)
0.1
(0.0-0.4)
2.2
(1.2-3.0)
2.9
(0.6-5.5)
2.3
(1.4-3.3)
Air- Exchange
Rate (h~l)
0.41
(0.1-0.87)
0.38
(0.21-0.55)
0.40
(0.21-0.57)
0.31
(0.18-0.45)
0.44
(0.15-1.22)
0.28
(0.14-0.60)
Radon Source
Magnitude3 '
(pCi I'1 h'1)
1.3
(0.0-3.3)
0.65
(0.3-0.9)
0.05
(0.0-0.2)
0.7
(0.4-1.3)
1.1
(0.3-2.6)
0.65
(0.1-1.4)
Arithmetic mean values for three-hour intervals; range of values given
in parentheses.
Occupied house, radon measured by CRM, air-exchange rates measured by
tracer gas decay one or two times per day.
Q
Occupied house, radon measured by CRM, air-exchange rates measured
continuously by tracer gas decay.
Unoccupied house, radon measured by CRM, air-exchange rate measured
continuously by tracer decay.
e _i _ I
The mean radon source magnitude is rounded to the nearest 0.05 pCi In.
124
-------
FIELD AND LABORATORY MEASUREMENTS OF RADON CONCENTRATIONS
IN MAINE HOUSES
C.T. Hess, C.V. Weiffenbach
University of Maine, Orono, Maine
H.R. Prichard and T.F. Gesell
University of Texas, Houston, Texas
ABSTRACT
Radon measurements using track etch cups and diffusion alpha detectors in
the field are compared with air grab samples and water grab samples measured
in the laboratory for 100 houses in Maine. These measurements have been taken
for the winter months from October 1980 to April 1981 as part of an on-going
year round study. Airborne radon concentrations ranging from O.05 to 21O
pCi/1 have been measured. Radon in water concentrations from 20 to 180,000
pCi/1 have been measured. A linear regression radon concentration in air
versus radon concentration in water is significant at the r = 0.5 significance
level for 40 laboratory samples of each. The concentration of radon in air is
1.3 pCi/1 for 10,000 pCi/1 in water. Analysis of constant sources of radon in
air such as soil, bedrock, or building materials and variable sources of radon
such as radon rich water shows a strong inverse effect on concentration due to
building ventilation.
There has been great interest in indoor radon in houses in recent publica-
tions by Barnaby on radon in Swedish houses, (Ba 79), by Cliff on radon in
dwellings in Great Britain (Cl 78, Cl 79) , by Fleisher in Rochester, New York
(Fl 81), and by the U.S.E.P.A. in houses built on phosphate tailings piles in
Florida (US 75). Recommendations for changes have been made for radon levels
above 3 pCi/1 in homes. In Canada recommendations for changes have been made
for radon greater than 5 pCi/1, in places such as Uranium City, Saskatchewan
(Ke 78).
This paper presents the initial results of a cooperative project between
the University of Maine Department of Physics, and the University of Texas
School of Public Health to measure indoor air and water radon levels in 10O
houses in Maine. The radon in air was measured in the laboratory with using
96 grab samples and with 514 track etch cups. The radon in water was measured
in the laboratory using 100 grab samples from the same houses. The houses
were also sampled for uranium in water and were characterized for fuel used,
estimate of ventilation, presence of granite building materials, and with
types of construction, number of residents, and volume of house. The survey
took place in October, 1980, through May, 1981, and is part of a year round
study of radon level in houses. The initial grab samples, of air and water,
and the initial place of Terradex - Fl track etch cups with paper filters took
place in October, 198O, and the cups were collected in April - May, 1981, and
then analyzed by Terradex Corp. The data thus represents radon levels during
125
-------
fall and winter months, when the ventilation is at a minimum in Maine. The
track etch cups were placed in bedroom, bathroom, living room or kitchen,
basement, and outside on a porch. The grab sample of 5 liters of air was
collected in Tedlar or heavy plastic bags, in the kitchen or living room of a
house, while students were collecting the information about the house. The
water sample was then taken after the water was allowed to flow in a sink for
at least 10 minutes to permit fresh water to be brought up out of the well.
The 10 ml water sample was taken with a syringe and placed in liquid
scintillation vials with 10 ml mineral oil fluor and analyzed for 40 minutes
with a commercial liquid scintillation counter. Samples were standardized
with radium solutions; for further details see the method of Prichard and
Gesell (Pr 80) . A 10 liter water sample was taken and acidified with 10 ml
1 normal HC1 for radium or uranium analysis. Track etch cups were provided by
the U.S.E.P.A. Laboratory in Las Vegas, Nevada and analyzed with low
sensitivity and high sensitivity depending on the density of tracks. After
the cups were exposed for 6 months - 7 months, the cups were collected, sealed
together with plastic inserts and stored in Tedlar bags until returning them
to be measured at Terradex Corp. in California. Cups were identified by track
etch cup number and house code number.
The houses measured were taken from a group of houses previously studied
for radon in water. The houses were selected for a high radon in water group
and a low radon in water group. Three fourths of the houses were measured by
student teams and one fourth by the State of Maine Department of Health En-
gineering. All the cups were handled in the same way and the survey is being
continued this summer using multiple cups at the same point in the house. Of
the original 53O cups, 513 have been used and measured, a return of more than
95% of cups placed.
Radon in air was measured in the grab samples by extracting the radon in
-70°C Hexane, and counting it with commercial liquid scintillation counters.
Additional data were collected in several houses using electronic diffusion
alpha detectors of the Wrenn type (Wr 75) . The diffusion alpha detector was
calibrated using National Bureau of Standards radium sources and recalibrated
at the Eastern Environmental Measurements Laboratory, and other university
laboratories, at the University of Texas and University of Maine, and
U.S.E.P.A. lab at Montgomery, Alabama. The alpha measurements of radon were
taken over a period of two days to 7 days at 10 minute intervals. These
measurements were used to determine the variation of radon with time in a
variety of houses with various sources of radon in air. The data was analyzed
for peaks and compared to records of water use and changes in ventilation.
Analysis of pulse shapes permitted determination of ventilation times for some
of the houses.
RESULTS
The radon in air values for grab samples of air ranged from .03 to 201
pCi/1 while the track etch cups ranged from 0.06 to 132 pCi/1. These values
are illustrated in Figure 1 which compares the grab sample taken in October
126
-------
with the average value for the track etch cup taken from October through May.
The data are correlated significantly with r = 0.991, with a slope of 1.49 and
an intercept of -0.48 pCi/1. This result may show a systematic measurement
difference or may show a difference in average ventilation. To test average
radon levels due to radon from water, which ranged from 20 to 115,000 pCi/1,
plots were made of bathroom air measured with track etch cups versus radon in
water concentration. These results are shown in Figure 2. This data has a
slope of 0.107 and an intercept of 1.59 with r = .307, n = 85 significance. A
similar curve was made for radon in the basement air measured by track etch
cup and water radon concentration in Figure 3. The data has a slope of O.127
and an intercept of 4.49 with r = O.151 significance. A summary of all data
for track etch cups versus water radon is shown in Table I. Surprisingly, the
highest value for slope is for radon in basement air versus radon in water.
Significant lower slopes are shown for all bathroom and kitchen-living room.
Histograms number of occurrences versus radon levels by room, measured
using track etch cups are shown in Figure 4. The average values for radon in
air are shown with arrows and are as follows; bathrooms 3.51 _+ 7.12, bedrooms
3.10 + 6.98, kitchen-living rooms 3.21 + 8.27, basement 6.79 + 16.8, outside
0.83 _+ .79. Since the radon is highest in basements, this shows that a major
source is associated with soil gas, or water radon in floor drains, or base-
ment building materials. Reductions on the second floor are by 2, and reduc-
tions on third floors are also observed to be factors of 2 from two story
house data. Error estimates are taken for the data to simulate a normal
distribution.
By using calibrated Spitz-Wrenn meters (Wr 75) , measurements have been
made of levels of radon in air during water uses such as showering, dish wash-
ing, and clothes washing. The fraction of radon lost ranges from 50% to 95%
for these activities (Pa 79). Weekly averages of the radon in the 20 houses
showed radon levels from 0.5 pCi/1 to 87 pCi/1 during the heating season.
Occasional radon daughter measurements by the method of Kusnetz (Ku 56) showed
equilibrium of daughters from 0.3 to 0.5. Portions of records of radon con-
centration in air of three houses A, B and 18 are shown in Figures 5 and 6.
House A has the highest levels we have found. This house, with an average of
87 pCi/1 is a solar heated house with connected greenhouse built on granite
bedrock with 2 feet of granite gravel fill. House B shows no 222Rn contri-
bution other than water supply. These results show that the radon in water is
not always the most significant source of radon in the air; but that radon in
water usually high when radon from all sources is high. Other sources include
granite blocks in basement walls or granite gravels in concrete or direct
emanation into houses from granite through soil and foundations.
Results exhibiting the variation of radon in air in homes with the radon
in the water are summarized in Figure 7. The open circles represent average
radon in the air due to water supply only obtained by considering only the
radon appearing during times of major water uses and which decreased with time
according to apparent ventilation rates of the houses studied - see Figure 5.
For the component of radon due to water, the radon levels in the air have been
normalized to these levels expected for a ventilation rate of one air change
per hour. The unadjusted average radon levels are also plotted as asterisks
for all the houses studied. All data presented are for winter, with minimum
ventilation in the houses. Since summer ventilation decreases levels in
houses, the expected exposures from radon in these sixteen houses range from
0.01 to 14 working level months per year.
127
-------
TABLE I
Bathroom
Kitchen/Living
Room
Bedroom
Basement
Outside
Slope
0.107
0.106
0.069
0.127
0.0085
Intercept
1.59
1.58
1.81
4.49
0.710
Signif .
0.307
0.216
0.198
0.151
.218
No. Pts.
85
71
84
79
68
No .2.3 pCi/1
23
15
17
38
2
Mean
3.39
3.11
2.98
6.44
0.84
S.D.
6.9
7.9
6.7
16.1
.78
128
-------
References
Ba79 Barnaby, W. 1979, "Very high radiation levels found in Swedish
houses." Nature 281, 6.
Cl 78 Cliff, K.D. 1978, "Assessment of airborne radon daughter concentrations
in dwellings in Great Britain." Phys . Med . Biol. 23, 696.
Cl 79 Cliff, K.D., Davies, B.C. and Reissland, J.A. 1979, "Little danger from
radon." Nature 279, 12.
Fl 81 Fleischer, R.L., Mongro-Campero , A. and Turner, C.G., 1981, "Radon
levels in homes in the Northeastern United States." Second Special
Symposium on Natural Radiation Environment Bhabha Atomic Research
Center, Bombay, India.
US 75 United States Environmental Protection Agency (1975). Preliminary
findings: radon daughter levels in structures constructed on reclaimed
Florida phosphate land. Technical note, EPA ORP/CSD 75-4.
Ge 79 George, A.C. and Breslin, A.J., 1979, "Distribution of ambient radon
and radon daughters in New York - New Jersey residences." Paper in
Proc. Nat. Rad. Environ III Edited by Gesell, T.F., Lowder, W.M. and
Mclaughlin, J.E. Con. 780422 (Dept. of Energy, Washington).
Ke 78 Keith Consulting, 1978, Report on investigative and remedial measures,
radiation reduction and radioactive decontamination in Uranium City,
Saskatchewan for the Atomic Energy Control Board of Canada. Keith
Consulting of Regina, Prince Albert, Lethbridge, Edmonton, Canada.
Pa 79 Partridge, J.E., Horton, T.R., and Sensintaffar , E.L., 1979, "A study
of radon -222 released from water during typical household activities"
U.S.E.P.A. Technical note ORP/EERF-79-1 Eastern Environmental Radiation
Facility, Montgomery, Alabama 36109.
Pr 77 Prichard, H.M. and Gesell, T.F., 1977, "Rapid measurements of
concentrations in water with a commercial liquid scintillation
counter-" Health Physics 33 No. 6, 577-581.
Pr 81 Prichard, H.M., 1981 "The measurement of radon-222 in air by direct
extraction into a liquid scintillator -" International Meeting on
radon-radon daughter measurements, Montgomery, Alabama.
Wr 75 Wrenn, M.D., Spitz, H. and Cohen, N. , 1975, "Design of a continuous
digital output environmental radon monitor-" IEEE Transactions of
Nuclear Science N.E. -33, 645.
Ku 56 Kusnets, H.L., 1956, "Radon daughters in mine atmospheres: A field
method for determining concentrations." AM . IND . HYG . Q. 17(1):
85-88 .
129
-------
FIGURE CAPTIONS
Figure 1. Radon concentration in air pCi/1 measured by track etch cups from
October, 1980 to May; 1981 and grab samples of air taken in October,
1980.
Figure 2. Radon concentration in bathroom air measured by track etch cups
versus radon in water measured by liquid scintillation.
Figure 3. Radon concentration in basement air measured by track etch cups
versus radon in water measured by liquid scintillation.
Figure 4. Histograms of number of occurrences of radon levels by room measured
with track etch cups versus concentration of levels in the room for
outside air, kitchen/living room air, bedroom air, bathroom air and
basement air. Average values indicated by arrows.
Figure 5. Radon concentration in air for two different houses measured by
diffusion alpha detectors at 10 minute intervals versus time of
day: a) open window to outside; b) close window to outside; c) run
clothes washer; d) shower; e) partially close off greenhouse from
house; f and g) showers; h) dishwasher; i) bath and shower. Note
for houses the effect of individual water uses in comparison to
background 222Rn-
Figure 6. Radon concentration in House 18 versus time of day for 6 days, noon
marked with n. Showers are marked with letter s, baths with letter
b, laundry with letter 1 and dishwasher marked with letter d.
Figure 7. Mean values over two to seven days at radon in air of homes during
the heating season. Asterisks are for uncorrected for ventilation
while circles are corrected for ventilation.
130
-------
U)
12
133.0,201.0 24.5,23.3
RADON IN AIR (pCi/L)
TRACK ETCH CUPS
VERSUS GRAB SAMPLES
8
TRACK ETCH CUPS
12
16
TO
e
H
ID
-------
-I
115.8
53.3
34.4
X
m^m
0
a
«8^
Co
tsj
•
RADON IN AIR VERSUS
RADON IN WATER FOR
THE BATH
—T
8
24 40 56
RADON IN WATER (nCi/L)
72
H-
W
H
-------
24
»
O
a
to
U)
O 8
o
133.0 54.6
RADON IN AIR VERSUS
RADON IN WATER FOR
THE BASEMENT
115.8
8
24 40
RADON IN WATER (nCi/L)
56
72
TO
e
H
tD
-------
tf)
111
o
OUTSIDE
.8
KITCHEN/LIVING
3.1
BEDROOM
3.0
BATHROOM
3.4
BASEMENT
6.4
U)
8 0
80 4 8
RADON IN AIR(pCi/L)
0
Figure 4
-------
Figure 5
150-
100-
50-
* 0
- 15-1
c
oc
10-
t,
5-
0-t
HOUSE A (28nCi Rn/l WATER)
abed
HOUSE B (27nCi Rn/l WATER)
i
12
24 12
TIME OF DAY
24
135
-------
Figure 6
10-
5-
0-
HOUSE
.•.'•'•• '
*i* * *S* »*..**
'
I
b
18 ( 18 nCi Rn/ 1 water) /':•'••
• "'••••..
"' '"Vl"
'•""fit ' 't
III 1 s
n
n
<
\
c
tc
o
a.
10-
5-
0-
• * »
•••."••,.. "''., ,...•„ •'.,./, ••"..,-•
'"./••" '... ,.•''
d ^ •'••''
n
10-
5-
0-
' i " "" "" ~>~r-
h d
•-'"'""'""t'H t!
slbll
TIME (n= noon)
136
-------
Figure 7
12
ORADON FROM WATER
* RADON FROM ALL SOURCES
20 4O 60
RADON IN WATER SUPPLY, nCi/l
137
-------
SURVEYS AND DECISION MAKING IN
A REMEDIAL ACTION PROGRAM
A.G. Scott
DSMA Acres
4195 Dundas Street, W.
Toronto, Ontario, Canada
ABSTRACT
As the observed frequency distribution of grab WL measurements in houses
was found to be lognormal with a GSD of 2.0, lognormal sampling theory was
used to guide the choice of sampling frequency for an extensive survey program
in over 500 houses. Analysis of lognormal data is illustrated by a Monte
Carlo sampling simulation.
The tasks of the survey portion of the Remedial Action Program at Elliot
Lake are:
1. identify those houses with annual average WL's in excess of the
action criterion of 0.02 WL,
2. demonstrate that the annual average WL is below 0.02 WL in those
houses where remedial work is not carried out,
3. demonstrate that the annual average WL following remedial work is
less than the action criterion of 0.02 WL.
The program started in July 1977, and the belief at that time was that the
elevated WL's in houses were due to the presence of radioactive contamination
adjacent to the houses. As a result, relatively few WL measurements were
made, the major effort being in gamma-ray survey. By late 1977 it was clear
that radioactive contamination was not the major cause of elevated WL, and a
systematic WL survey would be required to identify problem houses. The survey
would have to be based on repeated grab-samples, as that was the only equip-
ment available at the time.
By then sufficient WL measurements had been made to show that the distri-
bution of WL measurements over a period of time in individual houses was near-
ly lognormal with a geometric standard deviation (GSD) of approximately 2 (see
Figure 1). As a result of this, sampling theory for the lognormal distribu-
tion was reviewed to determine sampling strategy as a basis for survey organi-
zation. Fortunately many pollutants also have a lognormal distribution, and
so our task was greatly simplified by the use of a NIOSH publication (NI 75)
on this subject.
138
-------
U)
1UU
on_
OU
20-
in -
8 -
c _
D —i
A -
0 _
1
0
1
HOUSE #50
X = 39
GSD = 2.03
OBSERVED
^t
S
a/
£T
1
X
/
/
3
7
/
D 5
^
x
D ;
A
*
/
rO 9
s®
/fi
x""
^
^
GENERATED
THEORETICAL
GENERATED +
TUCHDCTTP Al
1 HhUKh 1 ILAL
J = 2 0
GSD = 2.0
D 95
? 9!
3.9
CUMULATIVE FREQUENCY (%)
FIGURE 1
-------
Figure 2 is copied from (NI 75) and shows the variation of the 2 sigma
confidence limits on the mean of a lognormal distribution with the number of
samples taken and the GSD of the distribution. For a GSD of 2.0, at least 9
measurements are required to reduce the confidence limits to below 50%, and a
large number is required to reduce the limits to less than 40%. From a prac-
tical point of view, there was little gain in accuracy in taking more than 10
independent measurements, and so that number was chosen as the minimum number
of samples in a survey. For convenience, the "annual average survey" was set
at 13 measurements, as this fitted with an initial measurement followed by a
sample a month over a 12 month period.
As readings tend to be higher in the summer, it is necessary to take read-
ings over a full year to avoid biasing the results according to season. There
will still be a slight theoretical bias in the estimate, for the samples are
not truly distributed at random, since they are not taken at night nor at
weekends which together comprise nearly 3/4 of the year. However, this is
unavoidable in practice.
To avoid waiting to start remedial work until a year's survey was complet-
ed, a set of rules based on "distribution free" statistics was generated to
identify those houses where the annual average was clearly in excess of 20 mWL
so that they could receive prompt remedial work.
When enough readings have been made to end the survey, the average WL in
the house is calculated. For those houses where the average is less than or
equal to 20 mWL, the data are sent to the RAP manager at the AECB* for
review. If he agrees that the average is probably less than 20 mWL, he issues
the homeowner a letter to that effect. If he feels that the calculated aver-
age is not fully representative of the average in the house, he may request
extra survey readings, or that remedial action be carried out in the house.
For those houses where the average is greater than 20 mWL, the data are
sent to the RAP manager for review. The AECB then contact the homeowners to
obtain their agreement to remedial work.
After the remedial work is completed, a Post Remedial Survey is carried
out to show that the WL in the house has been successfully reduced to less
than 20 mWL.
Major restoration of finish and appearance is not started until this sur-
vey is completed. As the homeowner is naturally interested in completion of
remedial work as soon as possible, a rapid answer is required.
The procedure adopted is to take 1 WL measurement a day for 10 consecutive
working days. If the best estimate of the mean is less than 0.02 WL, the
house is forwarded to the RAP manager as probably complying with the primary
criterion. The Compliance Division of the AECB subsequently check these
houses to verify that the WL has been reduced. The interrelationship between
the survey, the remedial program, and the AECB is shown in Figure 3.
AECB-Atomic Energy Control Board. The AECB directs the Remedial Action
Programs carried out and financed by the Joint Federal Provincial Task
Force on Radioactivity.
140
-------
160%
5678
NUMBER OF GRAB SAMPLES
10
11
0%
Figure 2 - Effect of small grab sample sizes on requirements for
demonstration of noncompliance. Three different data
geometric standard deviations (GSD) are shown which
reflect the amount of variability in the environment.
141
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DSMA/ACRES
SELECT PREMISES
FOR SURVEY
1
PREREMEDIAL
INVESTIGATION
STAGE 1
PREREMEDIAL
INVESTIGATION
STAGE 2
FIX \N_
DETERMINED /
DISCUSS FIX WITH
OWNER AND AECB
ALLOCATE TO A
TENDER GROUP
FIX
PASSES POST \N_
REMEDIAL SURVEY /
Yl
AECB
_V AECB ACCEPTS
\ SURVEY RESULTS
ACCESS
AGREEMENT
OBTAINED
Y
MEETS
CRITERION
OWNER
NOTIFIED
AECB ACCEPTS \N
SURVEY RESULTS
FIGURE 3
REMEDIAL PROGRAM LOGIC DIAGRAM
142
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As a large number of houses (500+) were under survey, it was not practical
to keep an overview of the program by manual summaries. Therefore, a computer
accessible data base was developed which lists the survey readings made in a
house, produces estimates of the house average WL and also keeps track of the
progress of the house through the remedial action program.
A demonstration of the analysis problems posed by the lognormal distribu-
tion, a Monte Carlo sampling simulation was carried out. Figure 4 shows a
histogram of 5500 numbers generated randomly from a lognormal distribution
with mean 20 and GSD of 2.0. If these 5500 lognormal numbers are analyzed in
the usual manner (which assumes a gaussian distribution) the mean is 19.7 and
the standard deviation is 15.6. The gaussian with these parameters is shown
in Figure 4, and can be seen to be a rather inadequate description of the
actual distribution of numbers. Approximately 16% of the numbers would have
to be negative for the gaussian to apply.
However, we do not make decisions based on a single reading, but only on
the average of groups of readings. It is our practice to take at least 10
readings in a house before we make any statistical decision, and so it is the
frequency distribution of samples of 10 that is of interest. This distribu-
tion was obtained by taking 550 groups of 10 numbers from the 5500 lognormal
numbers generated earlier. The arithmetic mean and the best-estimate mean
were calculated for each group of 10. The best-estimate mean is based on the
logarithmic mean of the sample numbers, and is the theoretically correct
method to estimate the average value of a lognormal distribution from a
sample. Figure 5 shows the CDF of the 550 best-estimate means. They are
lognormally distributed as expected, with variability reduced close to the
theoretical value of GSD = 1.25. The distribution of arithmetic means was
virtually identical to this, showing that the uncertainty in the estimate of
the mean was not a function of the method of analysis, but of the variability
of the measurements themselves. The slight asymmetry in the distribution does
require the confidence limits to be asymmetric, and so confidence limits based
on gaussian analysis will be incorrect. For example, gaussian analysis of the
5500 numbers gives 95% confidence limits on the mean groups of 10 samples as
11.6 and 27.8. Figure 5 enables the 95% confidence limits to be read direct-
ly. They are approximately 13 and 28.5, which are close to the gaussian
values, but slightly higher.
In practice the use of confidence limits creates yet another problem -
what to do in the case of those measurements that fall between the confidence
limits. For example, if we wish to work to 90% two tailed confidence limits,
and we make 10 measurements, Figure 5 shows us that we can make no decision if
the mean of the measurements is more than 13 mWL and less than 28.5 mWL. Now,
the one thing we cannot do in the real world is to take measurements and then
fail to make a decision, and although we can narrow the limits by taking more
readings, the zone of indecision cannot be removed completely except by an
arbitrary decision. We prefer to make our arbitrary decision first, and so
for our surveys we work at 50% confidence. At this level there is no zone of
indecision, and it has the intuitively appealing feature that we apparently
believe the average of our measurements when it comes to deciding if the
annual average WL in a house is, or is not, greater than 20 mWL.
143
-------
o;
LU
CO
GENERATED
DISTRIBUTION
GAUSSIAN ESTIMATED
FROM MEAN AND VARIANCE
OF GENERATED DISTRIBUTION
200
150
100
50
-30
70 80
FIGURE 4
-------
BEST ESTIMATE MEAN AND
ARITHMETIC MEAN
30 50 70 90
Cumulative Frequency (%)
DISTRIBUTION OF MEANS - GROUPS OF 10
FIGURE 5
99.9
-------
REFERENCES
Ni 75 "Statistical Methods for the Determination of Non-compliance with
Occupational Health Standards." HEW Publication No. (NIOSH) 75-159,
April, 1975.
146
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AIRBORNE Rn-222 IN BUILDINGS CONSTRUCTED WITH
HIGH-RADIUM-CONTENT CONCRETE BLOCKS
Bernd Kahn, Marcia Wilson and John T. Gasper
School of Nuclear Engineering and Health Physics
Georgia Institute of Technology
Atlanta, Georgia 30332
ABSTRACT
The relation of Rn-222 in building air to Ra-226 in structural materials
was examined by measuring the Rn-222 flux density at surfaces and
concentration in air in two office and laboratory buildings. The buildings
have walls constructed partially with concrete blocks that contain Ra-226 at
relatively high levels. The Rn-222 flux density at walls and floors was
measured by gamma-ray spectral analysis of charcoal collectors for radon that
had been sealed to surfaces for 3-day periods. The Rn-222 concentration in
air was measured by collecting air in evacuated 125-cc radon scintillation
(Lucas) cells and counting alpha particles in the cells. Results were
compared with samples collected outside and in a building that did not have
elevated Ra-226 levels in structural materials. To determine source terms,
Ra-226 concentrations were measured in building materials and soil.
Contributions to the Rn-222 concentration in building air from the ground
beneath the building, outside air, and construction materials were estimated.
The identified sources contributed between 67 and 100 percent of the average
of measured concentrations; in every instance, most of the Rn-222 was from the
ground beneath the building.
147
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INTRODUCTION
Some concrete made from phosphate slag contains elevated Ra-226 levels.
Buildings constructed with this concrete were identified in surveys through
increased external radiation exposure rates due to the gamma radiations that
Ra-226 and its Pb-214 and Bi-214 progeny emit. Exhalation of the gaseous
Rn-222 daughter from concrete walls, floors, or pillars into building air will
also increase the radiation dose to the lungs. This dose is due to alpha
particles emitted by the Po-218 and Po-214 progeny, at concentrations usually
specified in terms of the working level (WL). An increased WL value is
generally considered to indicate a greater hazard than the accompanying
external exposure rate in a building, but is not as easily quantified because
radon and its progeny in building air fluctuate widely. Complicating factors
in determining Rn-222 levels in air due to building materials are the
dependence of these levels on the ventilation rate and the fraction of Rn-222
emanating from the material, as well as relatively high levels from other
sources. This report describes measurements of Rn-222 concentrations in air
and exhalation rates from surfaces to distinguish among the sources of Rn-222
in air in three buildings, two of which were built with concrete blocks that
contain high-radium phosphate slag.
The slag from the thermal process for phosphorus production is a calcium
silicate that has been used variously for the fine and coarse aggregate in
concrete (Bo77, He79). Phosphorus plants in Idaho (Bo77, Pe78), Montana
(L178) and Alabama (Ma78, Ka79) have produced slags that contain Ra-226 at
concentrations between 30 and 60 picocurie per gram (pCi/g). The Ra-226
concentration in concrete depends on the Ra-226 level in the slag derived from
phosphate rock and on the fraction of slag used in the concrete. Radiation
exposure rates of approximately 40 microroentgen per hour (uR/hr) have been
measured in structures built with this material (Bo77, Ka79). In comparison,
exposure rates in buildings due to cosmic rays and Ra-226, Th-232, and K-40 in
building material and the ground usually range from 6 to 18 uR/hr (Ka79).
The EPA had proposed rules under the Resources Conservation and Recovery
Act of 1976 to prevent use of byproduct materials such as phosphate slag if
they increase gamma ray exposure rates by 5 uR/hr or WL values by 0.03. At
equilibrium, 0.03 WL results from a Rn-222 concentration of 3 picocurie per
liter (pCi/L). In buildings, the ratio of WL to Rn-222 concentrations
normally is well below this value, but differs according to various
conditions. The short-lived progeny do not attain equilibrium due to air
turnover and deposit on surfaces to some extent. Mixtures of Rn-222 and
progeny in building air typically result in approximately 0.004 WL per pCi/L
(UN77). Increases of 5 uR/hr and 0.03 WL or the corresponding 7.5 pCi/1 are
readily detected.
A number of reviews have considered Rn-222 in building air and its sources
(Co81, Ea75, Ha78, Ka79, Le81, Mo76, NC75, OE79, Ta80, UN77). Elevated Rn-222
concentrations in building air can be due to high concentrations in outside
air, the ground beneath, or the water or gas supply. Initially low levels can
rise steeply due to accumulation of radon and its daughters within a tightly
closed room or structure (Sp80). The Rn-222 concentration in outside air is
typically a few tenths of a pCi/L, but may fluctuate in the course of the year
148
-------
by almost two orders of magnitude at a single location (Ha78a). Radon inflow
from beneath the building is particularly apparent in houses built on uranium
tailings and at locations of former phosphate mines (Gu80, Ea75).
Average WL values in buildings not known to be associated with any
elevated Ra-226 levels appear to be between 0.003 and 0.007 WL (Ka79, Ge80)-
Because of the above-cited factors, the individual values on which these
averages are based may vary by almost two orders of magnitude among the
buildings included in a particular survey.
Radon-222 progeny levels in buildings constructed with high-radium
concrete were between 0.0005 and 0.05 WL in 107 structures in Idaho (Pe78);
between 0.001 and 0.1 WL (except for one higher value) in 69 Montana houses
(L178); and averaged 0.018 WL in 17 Alabama houses (US80). These measurements
were performed for extended periods to determine average radiation doses. In
Montana, averages in two towns were 0.02 and 0.013 WL (US80). The log-mean
value of 0.006 WL in the Idaho town is reported to be the same as the normal
background, and the corresponding log-mean Rn-222 concentration of 1.4 pCi/L
is also approximately the same as in normal structures (Pe78, US80). The
Rn-222 concentration and WL value in outside air and the Rn-222 flux density
from the ground beneath buildings were not reported.
In this study, air samples for Rn-222 analysis were collected in brief
(1-minute) periods at 3 multi-story office/laboratory buildings located near
each other. In building NE, interior walls on the second and third, but not
the first floor, are of concrete blocks with a Ra-226 concentration of 19
pCi/g; in building ER, most walls, interior and exterior, on all three floors
were constructed with these blocks; while in building CE the building
materials are not elevated in Ra-226. The Ra-226 in all concrete except the
blocks was estimated to average 1.5 pCi/g on the basis of external radiation
exposure rates (Ka79). Air samples were collected simultaneously to compare
Rn-222 levels inside and outside, on the various floors of individual
buildings, and on corresponding floors in the three buildings. Samples were
collected in the mornings, when the highest levels for daytime occupancy were
expected due to the early-morning peak in Rn-222 concentrations outside and
the overnight accumulation inside while the buildings were closed. The
turnover rate of air within the three buildings was measured by releasing and
collecting a tracer gas.
The exhalation rate of Rn-222 from the concrete blocks was measured for
3-day periods in the NE and ER buildings and compared with that from poured
concrete walls in the NE and CE buildings. The Ra-226 content and Rn-222
emanation fraction (or emanation power) in crushed blocks was also measured.
The exhalation rates of Rn-222 from soil and through the floors of the three
buildings were measured to determine the relative contribution by the ground
to the total Rn-222 concentrations in air. The external radiation exposure
rate and Ra-226 concentration in surface soil were measured as possible
indicators of the magnitude of Rn-222 exhalation rates from the ground. The
Rn-222 concentration was measured in the public water supply to determine the
contribution of this potential source to radon levels in building air.
149
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PROCEDURE
The 3 measurement sites are combined office and laboratory buildings at
the Georgia Institute of Technology. The NE building is built on a slab and
is three stories high. Its outside walls are brick with some concrete and
metal panels; the inside walls are mostly of concrete block. The second and
third stories were added in 1965. Only the blocks on these floors contain
elevated amounts of Ra-226. The ER building was also built in 1965, except
for a small west wing added later. It has a basement that is above ground on
two sides, 2 floors above basement level, and a small partial third floor.
The exterior walls are concrete block faced with brick and some concrete and
metal panels above the basement; the interior walls are of concrete block.
Except in the newer wing, the blocks have the same elevated Ra-226 levels as
those in the NE building. The CE building, used as control, is much older.
It has a basement that is above ground on two sides, and three stories above
the basement. The walls are of poured concrete, faced with brick. All
buildings have structural supports and floors of poured concrete. The two
newer buildings are centrally air conditioned. The older building has window
or area air conditioners in most offices and laboratories, but the hallways
and a laboratory extending throughout the basement are not air conditioned.
Cylindrical cells (6.0-cm dia. x 9.4 cm outside) coated on the inside with
ZnS(Ag) scintillator were used to measure alpha particles from radon and its
progeny (Gu80). The cells have a quartz window at one end and a glass
stopcock at the other. The cells were evacuated to approximately 0.04
atmosphere with a vacuum pump before sample collection. They were counted
within a shield to keep out light by placing the window on a photomultiplier
tube. The cells were calibrated with standard Ra-226 solutions at 5 pCi/L
levels. The counting efficiency for combined Rn-222, Po-218, and Po-214 alpha
particles was 2.5 +_ 0.1 counts/disintegration of Rn-222. Before and after
each measurement of Rn-222, the detector background was determined. Each
sample was counted twice in succession. The presence of Rn-222 and the
absence of interference was confirmed by observing the 3.82-day half life of
Rn-222. The combined counting periods of the background measured before and
after counters were typically 1,200 minutes, and the two sample counts were
for a similar period. Intervals of 150 minutes between sample collection and
measurement and between cell flushing and background measurement were
maintained to assure decay of any unsupported short-lived radon progeny.
Air samples were collected by opening the stopcock of an evacuated cell
for approximately 1 minute. The cell was usually held 1 m above the floor in
the middle of corridors. Outdoors, air was collected 1 m above open ground
and several meters distant from the building. Weather conditions were
recorded.
The standard deviation of counting these samples, which is believed to be
the major source of random error, was typically 0.04 pCi/L, and the minimum
detectable level, defined as the 3-sigma counting error of the background, was
0.08 pCi/L. Three samples collected side by side on 9-6-81 (see Table 1)
measured 0.85, 0.81, and 0.86 pCi/L. Hence, differences by more than 0.1
pCi/L are considered significant.
150
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Table 1
Radon-222 Concentrations in Air, pCi/L
Date,
1981 Time Conditions
3-6 0910 S, NC, BW*
3-12 0845 S, NC, BW
3-17 0900 S, NC, LW
3-19 0900 S, NC, BW
3-23 0820 OC, LW,
rained earlier
7-8 1040 S, NC, LW
7-10 1040 S, NC, C
7-15 1030 S, NC, LW
7-21 1050 S, NC, LW
CE Building
out- base-
side ment 1st 2nd 3rd
<0.1 0.8 1.0
0.3
0.1 0.7 0.4 0.5
<0.1 0.4 0.1 <0.1
0.9
0.1 0.2
NE Building
out-
side 1st 2nd 3rd
<0.1 1.0 0.6
<0.1 1.0 0.5
0.2 1.5 0.9 0.6
1.0
0.2 1.1 0.6
1.5 0.7
1.3
ER Building
out- base-
side ment 1st 2nd
0.1 0.5 0.1 0.9
0.4 1.1
<0.1 3.2 2.9 2.2
3.7
0.2 2.9
-------
Table 1 (cont'd)
Date,
1981 Time Conditions
7-25 1040 S, NC, LW
7-28 0730 S, NC, LW
0930
1130
7-30 0730 OC, LW
0930 light rain
1130 at 11:30
8-4 0810 S, NC, C
8-6 0750 S, SC, LW
8-13 0830 S, SC, LW
CE Building
out- base-
side ment 1st 2nd 3rd
<0.1 0.6
0.3 1.9 0.5 0.4 0.6
NE Building
out-
side 1st 2nd 3rd
0.3 1.8
0.4 1.6
0.2 1.3
<0.1 0.9
0.2 0.8
0.3 0.5
0.6
0.2 1.3 0.9 0.8t
0.8
0.9
ER Building
out- base-
side ment 1st 2nd
0.2 3.5
0.3 2.6 2.9 2.1
3.2 2.2
en
K)
* S: sunny; NC: no clouds; SC: scattered clouds; OC: overcast; C: calm; LW: light wind; BW: brisk wind;
t triplicate samples
-------
The Rn-222 content in tap water collected in the CE building on 11-17-81
was measured in duplicate samples. Aliquots of 18 ml water were placed in
emanation tubes and radon was flushed from them into Lucas cells, which were
counted twice in succession for a total period of 1,300 minutes. The
background in these cells was measured before and after the samples for 500
minutes each. The lower limit of detection (3-sigma value of the background
count) was 0.6 pCi/L. The same water—Atlanta city water obtained from the
Chattahoochee River—is used in all three buildings.
The rate of air turnover was determined by releasing SF^ gas on separate
occasions on the lowest and second lowest floor of each of the three
buildings. Approximately 1 cc of the gas was released. Air samples of 1 cc
each were then collected in 2-cc plastic graduated syringes and injected into
a gas chromatograph (Varian model 3700). The SF£ peak was observed just
before the oxygen peak. The peak areas were measured for samples collected
generally at 10-minute intervals for one to two hours after gas release.
These areas were plotted on semilogarithmic paper as a function of time after
gas release to determine the air exchange (ventilation) rate,Xa, in hr~ -
The Rn-222 flux density was determined by collecting radon on activated
cocoanut charcoal (6 - 14 mesh) in cylindrical plastic containers and counting
the charcoal after ingrowth of the Pb-214 and Bi-214 progeny with a Ge(Li)
detector plus multichannel analyzer. The container has a 500-cc volume and is
filled with 200 cc charcoal (122 g) retained by a paper filter and metal mesh
at the bottom of the container. A plastic cover seals the container before
and after collection. The container was pressed tightly against the surface
to be monitored and sealed to it with putty; for soil measurements, the
container was pressed into the soil. Samples were collected for 3-day periods
and counted for 10,000 to 50,000 seconds, depending on the count rate due to
Rn-222 progeny. The count rate was corrected for background radiation due to
Rn-222 progeny in air and decay of Rn-222 during collection, between
collection and counting, and during counting. The measurement was converted
to units of picocurie per square meter per hour (pCi/m^hr) on the basis of
the counting efficiency of the detector for a 200-cc sample volume, the period
of collection, and the 80-cm^ surface area of the collector.
Measurements of Rn-222 flux density were performed on walls constructed of
high-radium concrete blocks and of poured concrete, on poured concrete floors,
and on soil near the buildings. Two of the samplers were left open to air in
the CE building and two were sealed with the cover for 3-day periods to test,
respectively, the extent to which still air collects on the charcoal and the
extent of leakage into the container. The open charcoal sampler collected the
equivalent of 500 pCi/nrhr. The closed container collected no Rn-222, at
the detection limit of 10 pCi/m2hr.
Concrete blocks from the NE, ER, and EA buildings (the latter a warehouse
constructed with high-Ra-226 blocks) were broken into small pieces, ranging
from powder to approximately 5 mm in diameter, and weighed 500-cc aliquots
were analyzed for Ra-226 concentration by gamma-ray spectrometer. To
determine the emanation fraction, a 10-gm aliquot was placed in a 50-cc glass
tube with stopcocks at each end, connected to a second 50-cc tube. The sample
was stored for 2 to 6 days at accumulate Rn-222 in both tubes. The connection
153
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between the two tubes was then closed and the air in the second tube
(containing no concrete) was flushed into an evacuated radon scintillation
flask. The measured volume was 40 percent of the air over the concrete
sample. The ratio of the Rn-222 emanation rate to the generation rate was
determined from the Rn-222 in the sample and the Ra-226 in the material,
corrected for decay of Rn-222 during collection, between collection and
measurement, and during measurement.
Soil samples were collected from open ground at the two locations where
the Rn-222 flux density had been measured outside each building. Volumes of
500 cc were scraped from the top 2 cm of ground. The samples were placed in
plastic 500 cc containers, weighed, and measured by gamma-ray spectrometry.
Radium-226 was determined in soil and pieces of concrete block in closed
plastic containers by measuring the 352- and 609-keV gamma rays of Pb-214 and
Bi-214, respectively. To check these values, the 186-keV gamma ray of Ra-226
and U-235 were also measured. It was assumed that 58 percent was due to
Ra-226 and the rest due to U-235, and that the Ra-226 gamma ray represented
3.5 percent of Ra-226 decays. The 583- and 911-keV gamma rays of Ra-228
progeny were used to determine Ra-228, and the 1,461-keV gamma ray was used
for determining K-40. The radium results are uncertain to approximately 5
percent because of uncertainties in the applied gamma-ray fractions. In
addition, the standard deviation of the count rate—5 to 10 percent—depends
on radionuclide concentrations and counting periods.
A Reuter-Stokes pressurized ionization chamber held 1 m above ground was
used to measure external radiation exposure rates at the same locations. The
detector was calibrated with a 10 mg Ra-226 standardized source.
RESULTS AND DISCUSSION
The measured Rn-222 concentrations in air listed in Table 1 average 0.6,
1.0 and 2.2 pCi/L respectively in the CE, NE, and ER buildings compared to 0.2
pCi/L outside. Each of these averages represents between 16 and 25
measurements. The averages are consistent with previous observations of much
higher Rn-222 concentrations that have been encountered inside buildings than
outside. Outside levels were near 0.2 pCi/L during extensive surveys in
Sweden (Hu56) and Austria (St80). Indoor concentrations in Austria averaged
0.6 pCi/L and ranged from <0.05 to 5.2 pCi/L; those in Sweden generally were
in the same range. Some much higher levels in Swedish houses were found
associated with low ventilation rates and concrete that contained alum shale
(Sw80).
Radon-222 concentrations measured in July-August were only slightly above
the March measurements in the CE and NE buildings, but much higher in the ER
building. Averages were as follows outside the building and inside on the
floor nearest the ground:
154
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Location March July-August
outside 0.1 pCi/L 0.2 pCi/L
CE basement 0.6 0.8
NE ground floor 1.2 1.4
ER basement 0.5 3.2
The increases in the CE and NE buildings may be associated with the increased
levels in outside air, but the large increase in the ER building must be due
to another cause.
Within each building, the highest concentration of Rn-222 was consistently
in the story nearest the ground, as summarized in Table 2. Levels in upper
floors of the same building were similar. The highest concentrations in
buildings are commonly found nearest the ground, particularly in basements
(Ge80). This observation gives support to the hypothesis that the main source
of RN-222 in building air is the flux from the ground beneath the building.
In the NE building, the elevated Rn-222 concentration on the ground floor,
which does not have the high-radium concrete blocks used on the upper floors,
suggests that these blocks are not the major source of RN-222.
The measurements on 7-28 (see Table 1) show the decrease of Rn-222 levels
outside between 7:30 and 11:30 A.M. This is consistent with previous
observations of diurnal fluctuations that result in a gradual increase at
night to a maximum near sunrise associated with stable atmospheric conditions
and possibly inversions during the night, and rapid decrease thereafter
(NC75)- The changing indoor Rn-222 concentrations at higher levels paralleled
those outside. Some of the reduction of Rn-222 concentrations indoors may be
due to greater air turnover as more persons used the building in the course of
the morning. The measurements on the morning of 7-30, undertaken on an
overcast day with relatively stable atmospheric conditions and light rain
beginning toward the end of the study period, showed relatively uniform Rn-222
levels outdoors and only a slight decrease in the building.
The highest exhalation rates were found at cracks and seams in the
concrete floors of the buildings, and at one location in the ground just
outside the ER building, as shown in Table 3. In general, the exhalation
rates were several thousand pCi/m^hr from soil and several hundred
pCi/m^hr from the concrete blocks. The flux densities at the floors nearest
the ground were much less where the floor was continuous than at cracks or
seams. The exhalation rates from poured concrete walls in the CE and NE
buildings, which have only ordinary Ra-226 contents, were between 10 and 100
A survey of exhalation rates from soil reported an average value of 1,500
^hr (0.75 atoms/cm^sec) and values that ranged approximately
three-fold above and below this average in the continental United States
(Wi72). Considerable fluctuation can be caused by changes in air pressure and
soil moisture content (Co81). The values in Table 3 for the soil near the CE
155
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Table 2
Average Rn-222 Concentrations In
Building and Outside Air
Location
CE
NE
ER
building
building
building
Outside
0.1
0.2
0.2
(6)*
(11)
(5)
Radon-222
Basement
0
2
• 7 (8)
—
.4 (7)
concentration,
1st
0.4
1.3
2.0
floor
(2)
(11)
(5)
2nd
0.5
0.7
1.8
pCi/L
floor
(4)
(10)
(4)
3rd
0.3
0.8
--
floor
(2)
(4)
-
Number of measurements in parentheses
156
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Table 3
Radon-222 Flux Density, pCi/m2hr
Date,
1981
9-11
9-15
9-18
9-25
9-28
9-29
10-16
10-23
11-20
CE Building
ground floor wall
2,100(SE) 4,630(C) 10
2,050(SW) 8,380(C) 14
2,040(SE)
2,150(SW)
220
680
NE Building
ground floor wall
3,430(E) 22,000(C) 580(W)
4,360(N) 48,300(5)
10,500(N) 270(E)
3,820(E)
6,790(N)
520(W)
360(E)
340
720
103
84
ER Building
ground floor wall
18,300(NE) 8,270(5) 75(W)
5,000(SW) 6,170(5) 220(E)
18,600(NE)
1,840(SW)
15(W)
210(E)
430
380
1,900(C)
Notes: 1. Letters in parentheses for ground and wall samples show direction
relative to building; for floor samples, (C) or (S) indicates
measurement over crack or seam, respectively.
2. Samples were collected for 3-day periods, beginning on indicated
date.
3. The wall samples labelled (E) and (W) were for high-radium concrete
blocks; all others were for poured concrete.
157
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building are near the cited average and were reproducible. Flux densities at
some of the other soil locations, however, were relatively high and differed
for successive 3-day sampling periods by factors between 2 and 3.
Flux densities between 30 and 650 pCi/m2hr (0.8 to 18 attocurie/cm2sec)
had been measured on cellar floors in New Jersey, where the Ra-226
concentration in soil averaged approximately 1 pCi/g (Ge80). The flux
densities measured on unbroken surfaces at the ground floors in the NE and ER
buildings were toward the upper end of this range. The high values above
cracks or seams undoubtedly are higher still relative to the area of the
breaks because most of the area of measurement was unbroken floor. As a
result, the flux density for the floor as a whole is higher than on unbroken
floor, and may reach the exhalation rate from the soil beneath the building
(Co81).
Application of the reported ratio of 20 pCi/m2hr (0.005 pCi/m2sec) per
Ra-226 concentration of 1 pCi/g in 10-cm-thick concrete (UN77) indicates that
most of the exhaled Rn-222 is from beneath the floor. This ratio also gives
the order of magnitude of the observed values for the flux density at poured
concrete and concrete block walls if their Ra-226 contents are 1.5 and 19
pCi/g, respectively.
The emanation fraction based on the flux density measured for four
concrete blocks in the walls averaged 3.0 percent (see Table 4) and ranged
from 0.5 to 5.7 percent. The calculation is based on an average Ra-226
daughter concentration of 19;+ 1 pCi/g measured in four blocks that had been
removed from walls in these buildings (see Table 5), and the average weight
and dimensions determined with these blocks. Note that all of these blocks
are hollow. The loss of 3 percent of the Rn-222 by exhalation would increase
the Ra-226 concentration to 19.6 pCi/g, consistent with the direct Ra-226
measurement (Table 5) of 20 pCi/g.
For comparison, the emanation fraction for two blocks from the EA building
that had been crushed was 3.9 percent, as shown in Table 4. These average
values of 3.0 and 3.9 percent are above the range of 0.2 to 1.5 percent
observed for 11 samples of Polish concrete that contain slag (Pe80). The
emanation fraction measured in 116 samples of ordinary concrete in Hungary,
however, ranged from 15 to 60 percent, with a log-mean value of 30 percent
(To80). Agreement between the Ra-226 and radium-progeny concentrations in 4
concrete blocks measured here supports a smaller emanation fraction.
The radioactivity levels in surface soil just outside the three buildings,
shown in Table 6, were relatively uniform. The overall Ra-226 average of 1.5
pCi/g is above the local average of 1 pCi/g, and the range of 1.0 to 2.6 pCi/g
is at the upper end of values between 0.4 and 2.6 pCi/g found in the Atlanta
area (Ka79). The measured terrestrial exposure rates listed in Table 6 are
consistent with the exposure rates calculated for the radionuclide
concentrations. These exposure rates were measured near the soil sampling
locations but represent a much larger area, thus providing a measure of
confidence that the few samples represent radionuclide levels near the
buildings. The terrestrial exposure rate was highest at the location of the
highest Rn-222 flux from soil, but the much higher flux density was not
158
-------
Table 4
Emanation Fraction of Rn-222 from Concrete Blocks
Block
NE (W)
NE (E)
ER (W)
ER (E)
EA
Exhalation rate,
pCi/m2hr
546 (2)a
316 (2)
45 (2)
217 (2)
—
Emanation fraction, %
5.7b
3.3
0.47
2.3
3.9C (3)
a Number of replicate measurements is indicated in parentheses.
b Complete exhalation from one side of a block would be 19
pCi/g x 0.95 g/cm3 x 7.0 cm x 104cm2/m2 x 0.00755
hr-1 = 9,450 pCi/m2hr.
c Amount of Rn-222 in air per weight of block, relative to
Ra-226 concentrations of 19 pCi/g.
159
-------
Table 5
Radionuclide Content of Concrete Blocks
Building
NE
ER
EA
NE
Average
Sampling date
1981
1981
1979
1979
Ra-226
22
21
18
--
20
Radioactivi
Ra-226 progeny
19
18
17
21
21
19
ty, pCi/g
Ra-228 progeny
0.9
1.2
1.0
1.0
1.0
1.0
K-40
9.9
9.7
7.0
7.7
9.4
9.1
Note: The last two sets of values are from Ka79, Table 4; block EA
was reanalyzed in this study as indicated.
160
-------
Table 6
Radium-226 Concentrations in Soil Outside
Buildings and Confirmatory Exposure Rate Measurements
Radionuclide concentration, pCi/g
Ra-226
Ra-226 progeny
Ra-228 progeny
K-40
Terrestrial exposure rate, yR/hr
calculatedt
measured**
CE
Buildi
1.
1.
1.
12.
7.
8.
5 ±
0 ±
3 ±
2 ±
7 ±
4 ±
ng
0.
0.
0.
1.
1.
1.
NE
Buildi
4*
2
1
3
2
1
2
1
1
12
8
8
.0 ±
.3 ±
.4 ±
.8 ±
.7 ±
.5 ±
ng
0.
0.
0.
0.
0.
1.
ER
Building
6
3
0
7
5
2
1
1
1
13
7
9
.4 ±
.0 ±
.3 ±
.0 ±
.9 ±
.8 ±
0.4
0.2
0.3
1.9
1.6
1.1
* _+ values are deviations from mean of duplicate measurements
t Calculated on basis of
I = 1.90 CRa_226 progeny + 2-82 CRa-228 progeny + 0.179CK_40
where C is concentration in pCi/g
** Measured with pressurized ionization chamber; 3.8 yR/hr cosmic-
ray exposure rate has been subtracted
161
-------
proportional to the incremental exposure rate above the average. The reported
ratio of 2,000 pCi/m2hr (0.5 pCi/m2sec) per soil Ra-226 concentration of 1
pCi/g (UN77) is consistent with observed values except for the highest
exhalation rate near the ER building. The Ra-226 level of only 1.8 pCi/g at
the surface suggests that the much higher Rn-222 flux density must be
attributed to elevated Ra-226 concentrations well below the surface or freer
movement of radon through the soil at that location.
Five of the six ventilation measurements obtained on each of the two lower
floors in the three buildings yielded rates near 1 per hour, as shown in
Figure 1. These rates of exchange of inside with outside air are consistent
with the previously reported range in buildings (Ha73). The very high
turnover rate for the first floor of the CE building was not used in
calculations because the nearby open windows and doors during the ventilation
measurement were closed when Rn-222 concentrations had been measured.
The Rn-222 radioactivity level in a structure can be computed from the
following balancing of Rn-222 sources from the ground, building materials, and
outside air against radioactive decay and ventilation:
d GRn Sm1m Sgzgfw
= + - *Rn CRn - Xa (CRn - L0) (1)
dt V V
d °Rn
if = 0 (equilibrium) and \a »\ Rn (normal ventilation)
dt
m-^-m + Sglgfyr
GRn = C0 + (2)
Xa V
Im = 10^ CRa XRnfepw (3)
In the above equations, the symbols represent the following:
CRn : inside Rn-222 concentration, pCi/L
Co : outside Rn-222 concentration, pCi/L
t : time, hr
Sm : material surface, m^
Sg : ground surface, m^
Im : inward Rn-222 flux density from material surfaces, pCi ra
Ig : inward Rn-222 flux density from ground surface, pCi m~2hr~1
V : building air volume, L
162
-------
Figure 1
5,000 -
2,000 -
1,000 -
500 -
r. 200 -
100 -
1st FLOOR (A A) 1.38/hr
BASEMENT
(0 0) 1.24/hr.
2nd FLOOR
(V V) 1.34/hr.
1st FLOOR
(D D) 0.70/hr.
BASEMENT
(O 0)l.
1st FLOOR
(A—A) 4.5/hr.
60 70 80
TIME (MINUTES)
90
100 110 120 130 140
163
-------
: air turnover rate, hr"-"-
: Rn-222 decay rate, 0.00755 hr~l
fw : fractional Rn-222 diffusion through floor
: Ra-226 in material, pCi g~l
fe : exhalation fraction from material
P : density of material, g cm" 3
w : one-half of wall thickness, cm
In the presence of two types of wall materials, one containing more Ra-226
than the other ; the terms Smlm can be replaced by Smlm + Sm*Im*,
where the unstarred and starred terms refer to the low-radium and high-radium
materials, respectively.
The building dimensions, Rn-222 flux densities and other data in Table 7
were used to compute Rn-222 concentrations in building air. The value of V
applies to the entire building. The values of Sm refer to concrete and
brick surfaces, including outside walls, inside walls, and floors that are not
unusually elevated in Ra-226 concentrations, whereas Sm* refers to the
surfaces of concrete blocks with elevated Ra-226 content. The area of
basement walls facing soil was added to the floor area for Sg. The averages
of the pertinent measured flux densities in Table 3 were used for Im* at the
NE and ER buildings and for Im at all three buildings. The average flux
measured in soil near the building was used for !„ in preference to the
values measured on the lowest building floor. The differences between
measurements on unbroken floor and over cracks or seams were so large that it
was assumed that all of the Rn-222 from the ground entered the building
through passages through or around the floor (i.e., fw = 1.0). The air
turnover rate for a building is the average of the slopes of the pairs of
lines drawn through the data in Figure 1.
The Rn-222 concentration in tap water was 1.0 +_ 0.6 pCi/L. This value
indicates that water use is not a significant source of Rn-222 in building
air. At an estimated hourly water use of 1,000 litres, building volumes in
excess of 1 x 10? liters (see Table 7), and an air turnover rate of
approximately 1 per hour, the concentration of Rn-222 in building air from
water would be only 1 x 10~^ pCi/L. This estimate is consistent with the
expectation that water from a surface supply would contribute only minor
amounts of Rn-222 to building air (E079).
The results of these calculations, shown in Table 8, suggest that Rn-222
emanating from the concrete blocks high in Ra-226 has a concentration of 0.1
and 0.2 pCi/L in the NE and ER buildings, respectively. This contribution
would approximately double the concentration due to outside air. The concrete
materials at the usual lower Ra-226 level in the three buildings contribute an
extremely small fraction of the total Rn-222 in building air. The major
source of Rn-222 in building air appears to be Ra-226 in soil beneath the
164
-------
Table 7
Factors for Calculating Rn-222 Concentrations in Building Air
Building
dimensions CE Bui
plan, m2 40 x 16
14 x 11
height, m 5.5+2
V, m3 12,
Sm, m2 16,
Sm*, m
Sg, m2 1,
wp, g cm-2
Radon exhalation
and concentration
I , pCi m"2hr"1 2,
I , pCi m hr
Im*, pCi m-Zhr-1
CRa, pCi g-1
C*n3, pCi g"-1-
r\u
Air turnover
V hr-l
Iding
+ 27 x 4 +
(basement)
x 3.6 + 3.0
000
000
-0-
100
16.1 inside
39. outside
100
53
-0-
(1.5)
-0-
1.1
NE Building
69 x 27
3 x 3.0
17,000
15,000t
8,500
1,900
7.0
5,800
53
280
(1.5)
19
1.0
ER Building
65 x 29
3.7 + 2 x 3.0
18,000
11,000
17,000
2,100
7.0
10,900
53
280
(1.5)
19
1.2
* material with elevated Ra-226 content
t does not include outside panel walls
() assumed value
165
-------
Table 8
Calculated Rn-222 Concentrations
in Building Air, pCi/L
Source of Rn-222 CE Building NE Building ER Building
Outside air 0.1 0.2 0.2
Ra-226 in ground 0.2 0.6 1.1
Ra-226 in building
material - 1.5 pCi/g 0.06 0.05 0.03
- 19 pCi/g — 0.1 0.2
Total 0.4 1.0 1.5
Measured average 0.6 1.0 2.2
166
-------
building. The large increase in the Rn-222 concentration in ER building air
from March to July may be related to an increased exhalation rate from the
ground.
Differences between the measured and computed Rn-222 concentrations shown
in Table 8 may be attributable to the following sources of uncertainty: (1)
assuming that the Rn-222 flux density at the lowest floor equals that at the
ground outside (not considering partial retention of radon by the floor or
possibly higher flux rates from soil beneath the building than outside); (2)
averaging Rn-222 concentrations for various times and locations; (3) combining
concentration and flux density measurements not collected simultaneously or at
the same locations; (4) measuring flux density and ventilation rates on only a
few occasions; (5) using approximate values for building volumes and surface
areas; and (6) obtaining only a few measurements of Ra-226 concentrations and
Rn-222 emanation fractions.
SUMMARY AND CONCLUSIONS
In two office/laboratory buildings constructed in part with concrete
blocks that contain Ra-226 at the elevated level of 19'pCi/g, average Rn-222
concentrations in air were 1.0 and 2.2 pCi/L, respectively. Radon-222
concentrations averaged 0.6 pCi/L in a control building, and 0.2 pCi/L in
outside air. Samples collected simultaneously at comparison locations for
1-min periods showed that Rn-222 concentrations were highest nearest the
ground and similar to each other on upper floors.
Radon-222 flux densities averaged 53 pCi/m^hr from poured concrete with
normal Ra-226 levels and 280 pCi/m^hr from the concrete blocks with a Ra-226
concentration of 19 pCi/g. The emanation fraction of Rn-222 from the
high-radium concrete blocks averaged 3.0 percent on the basis of flux density
measurements on site and 3.9 percent for crushed block. The flux density at
the floor nearest the ground was several hundred pCi/m^hr over unbroken
concrete but one to two orders of magnitude higher over cracks and seams. The
flux density over soil near these buildings ranged from 2,000 to 18,000
According to calculations based on flux density and ventilation rate
measurements, the concrete blocks with elevated radium content contributed 0.1
to 0.2 pCi/L to the Rn-222 concentration in building air, equal to the Rn-222
concentration due to outside air during this period. Most of the Rn-222 in
air in the two study buildings and the control building is attributed to
Rn-222 exhalation from the ground, moving with little or no retention at
cracks, seams, and other passages through the concrete. The main differences
in building air Rn-222 concentration among the three buildings appear to be
due to differences in exhalation rates from the ground.
The calculated Rn-222 concentrations in air in two of the three buildings
were one-third below the measured values. Unless a source of Rn-222 has been
overlooked, these differences may arise from basing comparisons on averages of
relatively few measurements with large differences in flux densities and
concentrations. Assuring better comparability would require many more
measurements, obtained simultaneously.
167
-------
Despite the relatively elevated Ra-226 concentrations in the concrete
blocks and the extensive use of these blocks in the two buildings, the Rn-222
and inferred WL values in building air were low and the blocks apparently
contributed only a small fraction of these. At a typical ratio of 0.004 WL
per Rn-222 concentration of 1 pCi/L in building air, the highest average value
was 0.009 WL, and the value due to the high-radium concrete blocks was 0.0008
WL. Unless the ventilation rate is drastically reduced and, at the same time,
the emanation fraction of the blocks increases greatly, Rn-222 levels from the
blocks would not reach limiting levels in the two buildings. The magnitude of
the emanation fraction and its dependence on factors such as pressure,
temperature, and humidity changes is probably the crucial point in predicting
Rn-222 exhalation from building material, and requires considerable additional
study.
Acknowledgments: We thank Cornelia Jackson for collecting and measuring the
July samples of Rn-222 in air, Jacqualyn Gasper and John Oliver for measuring
ventilation rates, and Dr. John Garden for use of the gas chromatograph.
168
-------
REFERENCES
Bo77 Soothe G. F., 1977, "The Need for Radiation Controls in the Phosphate
and Related Industries," Health Phys. 32, 285.
Ca75 Caruthers L. T. and Waltner A. W., 1975, "Need for Standards for Natural
Airborne Radioactivity (Radon and Daughters) Concentration in Modern
Buildings," Health Phys. 2J), 814.
Co81 Colle R., Rubin R. J., Knab L.T., and Hutchinson J.M.R., 1981, Radon
Transport Through and Exhalation from Building Materials: A Review and
Assessment, NBS Technical Note 1139.
Ea75 Eadie G. G., 1975, "Radioactivity in Construction Materials, A Literature
Review and Bibliography," US EPA Rept. ORP/LV-75-1.
Ge80 George A.C. and Breslin A.J., 1980, "Distribution of Ambient Radon and
Radon Daughters in New York-New Jersey Residences," The Natural Radiation
Environment III, T.F. Gesell and W.M. Lowder, eds., US DOE Rept.
CONF-780422, p. 1237.
Gu80 Guimond R.J. and Windham S.T., 1980, "Radiological Evaluation of
Structures Constructed on Phosphate-Related Land," The Natural Radiation
Environment III, T.F. Gesell and W.M. Lowder, eds., US DOE Rept.
CONF-780422, p. 1457.
Ha73 Handley T.H. and Barton C.J. , 1973, "Home Ventilation Rates: A
Literature Survey," US DOE Rept. ORNL-TM-4318.
Ha78 Harley J.H., 1978, "Radioactivity in Building Materials," Radioactivity
in Consumer Products, A.A. Moghissi, et al., eds., Pergamon Press, New
York, 336.
Ha78a Harley J. H., 1978, "Radon-222 Measurement," Regional Baseline Station,
Chester, NJ, US DOE Rept. EML-347.
He79 Hendricks, D.W., 1979, "Elemental Phosphorus Plants," US EPA Office of
Radiation Programs, Las Vegas Facility, Las Vegas, NV, unpublished
memorandum.
Hu56 Hultqvist B., 1956, "Studies on Naturally Occurring Ionizing Radiations,
with Special Reference to Radiation Doses in Swedish Houses of Various
Types," Kungliga Svenska vetenskapsakademiens hadlingar, fjarde serien,
Band 6, nr 3, Stockholm.
Ka79 Kahn B., Eicholz G.G., and Clarke F.J., 1979, "Assessment of the
Critical Populations at Risk Due to Radiation Exposure in Structures,"
Report to Office of Radiation Programs, US EPA, NTIS No. PB 81-103764.
Le81 Lepman S.R. , Boegel M.L., and Hallowell C.D., 1981, Radon: A
Bibliography, USDOE Rept. LBL-12200.
169
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L178 Lloyd L., 1978, Montana Dept. of Health and Environmental Sciences,
Helena, Montana, personal communication.
Ma78 Maxwell R., Belvin E., and Reed R., 1978, TVA, Muscle Shoals, Alabama,
personal communication.
Mo76 Moeller D. W. and Underbill D.W., 1976, "Final Report on Study of the
Effects of Building Materials on Population Dose Equivalents," Harvard
School of Public Health, Boston, Mass.
NC75 National Council on Radiation Protection and Measurements, 1975,
"Natural Background Radiation in the United States," NCRP Rept. No. 45,
Washington, D.C.
Pe80 Pensko J. and Stpiczynska Z., 1980, "Emanating Power of Rn-222 Measured
in Building Materials," The Natural Radiation Environment III, T.F. Gesell
and W.M. Lowder, eds., US DOE Rept. CONF-780422, p. 1407.
Pe78 Peterson B.H., 1978, Idaho Dept. of Health and Welfare, Boise, Idaho,
personal communication.
OE79 OECD Nuclear Energy Agency, 1979, "Exposure to Radiation from the
Natural Radioactivity in Building Materials," Organization for Economic
Cooperation and Development, Paris, France.
Ta80 Task Force on Radon in Structures, 1980, Report of the Task Force on
Radon in Structures, U.S. Radiation Policy Council RPC-80-002.
To80 Toth A., Feher I., Lakatos S.N., Koszarus L., and Kezthelyi B., 1980,
"Distribution of Natural Radioactive Isotope Concentrations and Exhalation
Factors Measured on Concrete and Brick Samples Produced in Hungary," The
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DOE Rept. CONF-780422, p. 1396.
Tr79 Travis C.C., Watson A.P. , McDowell-Boyer L.M., Cotter S.J. , Randolph
M.L. , and Fields D.E., 1979, "Natural and Technologically Enhanced Sources
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1977, "Sources and Effects of Ionizing Radiation," United Nations, New
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in Structures," Rept. RPC-80-002.
Wi72 Wilkening M.H., Clements W.E., and Stanley D., 1972, "Radon-222 Flux
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170
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ENVIRONMENTAL RADON INVESTIGATIONS IN SWEDEN
Gustav Akerblom
Geological Survey of Sweden
Box 801
S-951 28 Lulea, SWEDEN
ABSTRACT
In Sweden, radon daughter concentrations of 200-800 Bq m~3 (0.05-0.2 WL)
are known to occur in some buildings constructed of areated concrete which
have been manufactured from alum shale, a Cambrium, uranium-rich black shale.
As a result of these alarmingly high levels, the Swedish government set up, in
1979, a Commission whose task is to initiate research around the problem of
radon, and to recommend remedial measures against natural radiation in
dwellings.
Based on the recommendations of the Commission, the Government proposed
the following measures:
the introduction of provisional limits for permitted radon daughter
concentrations in dwellings. These limits are 400 Bq m~3 (0.11 WL)
for existing buildings and 70 Bq m~3 (0.02 WL) for new development.
the use of specific building techniques when developing areas with
high soil gas radon contents.
an immediate search for all buildings constructed of alum shale based
on aerated concrete.
About 300,000 houses in Sweden are constructed entirely or partially of
aerated concrete containing alum shale. During 1980, radon daughter levels
have been measured in 20,000 of these houses by Local Health Authorities. The
first results show that about 14% of the measured houses have radon daughter
levels exceeding 400 Bq m~3. In about 2% of the investigated houses the
value exceeded 1,000 Bq m~3 (0.27 WL), and maximum values of 4,000 to 9,000
Bq m~3 (1.1 -2.4 WL) have been measured in some houses.
Radon daughter levels exceeding 800 Bq m~3 are not caused entirely by
radon emanating from building materials. A contribution of radon from the
ground is necessary. Most of the houses with values exceeding 800 Bq m~3
have proved to be sited on ground containing alum shale, uranium-rich granite
or uranium-rich pegmatite or on eskers. Many thousands of houses in Sweden
are built in such situations.
171
-------
The measurements so far obtained indicate that the problem of radon
penetrating into buildings from the ground is a far greater problem than that
of radon emanating from building materials. Geological and geophysical
investigations of risk areas are of the utmost importance if all new
development is to comply with the provisional limits for radon daughter levels
proposed by the Radon Commission.
INTRODUCTION
Approximately 300,000 dwellings in Sweden are constructed, either
partially or entirely, of radioactive aerated concrete. This concrete is
manufactured from alum shale, a uranium-rich (U 50-350 ppm), Upper Cambrian,
black shale which is sometimes sufficiently rich in organic matter that it may
be used as fuel. Alum shale occurs as a horizontal layer which varies in
thickness from 2-75 metres. The distribution of the alum shale occurrences
in Sweden is shown in Fig. 1.
The manufacture of alum shale base aerated concrete dates back to 1928.
It was known at the time, that the concrete and the alum shale from which it
was produced, had high uranium contents, but it was not until during the
1950's that the suitability of alum shale as a building material was
questioned (Hultqvist, 1956).
During the 1970's, high indoor radon levels were measured in houses built
of alum shale based aerated concrete, but manufacture of this material
continued until 1975. Indoor radon measurements made by the National Institute
of Radiation Protection during the 1970's revealed that radon levels in houses
increased in connection with energy saving measures. Houses were being made
more air-tight and rates of ventilation were being lowered. In some of the
houses investigated by the Institute, radon levels of 200 - 800 Bq m~3
(Becquerel per cubic metre) were encountered (Swedjemark, 1977, 1978 a and b,
1980) .
A new dimension to the radon problem became apparent in 1978 when the
National Institute of Radiation Protection measured radon levels in houses
built of normal materials on a foundation of alum shale tailings. The
measured levels were found to be between 400 and 1,600 Bq m~3 (Swedjemark,
et al 1979).
RADON COMMISSION
In February 1979, the Swedish Government appointed a Commission to
investigate measures against radiation hazards in buildings. The Commission
was also instructed to initiate a search for all such buildings, and to
promote research around the radon problem. The Commission is assisted by
various experts, for example, from the National Institute of Radiation
Protection, the National Board of Health and Welfare, the National Board of
Urban Planning, the Geological Survey of Sweden, the building industry and the
Swedish Association of Local Authorities. A preliminary report from the
Commission was presented in May 1979 (Radonutredningen 1979). The report
contains proposals on: provisional limits for the maximum radon daughter
levels in dwellings; maximum permitted radium content in building materials
and gamma radiation from these materials; searches for houses with high radon
daughter levels; and research programs.
172
-------
Figure 1
FINLAND
24° E
GULF OF BOTHNIA
LYSEKIL
65°N
NORWAY
ALUM SHALE
a KNOWN AREAS
I OF RADIOACTIVE
GRANITE >25,uR/h
OCKHOLM
100km
173
SGU 1981
-------
A further proposal made by the Commission in its report was that maps,
termed GEO-radiation maps, should be prepared to show the distribution in
Sweden of all areas with particularly radioactive rock and soils (alum shale
and uranium-rich granites and pegmatites). A full description of these maps
is given in Wilson (1981).
LIMITS
Acting on instructions from the Government, the National Board of Health
and Welfare and the National Board of Urban Planning in consultation with the
National Institute of Radiation Protection have issued provisional regulations
based on the proposals presented by the Radon Commission (Socialstyrelsen
1980, Statens planverk 1980). In short, the regulations are as follows
(complete text is given in Appendix 1.):
Existing houses
400 Bq m~3 (0.11 WL) is a provisional action limit for the annual
average of the equilibrium concentration of radon. Houses with levels
exceeding 400 Bq m~3 are declared to be insanitary.
After remedial action or building alterations, the annual average of the
equilibrium equivalent concentration of radon shall not exceed 200 Bq m~3.
New development
70 Bq m~3 (0.02 WL) is the maximum permitted limit for the annual
average of the equilibrium equivalent concentration of radon in rooms which
are in continual use.
50 yR/h (micro Roentgen per hour) is the maximum permitted gamma radiation
for rooms in continual use.
Building materials
Building materials for use in continuously inhabited constructions shall
not have a gamma index or radium index exceeding 1.0. It is also recommended
that gamma radiation shall not exceed 100 pR/h for outdoor areas which are
in regular use, for example, playgrounds.
The gamma and radium indexes are defined as follows:
CK CRa
Gamma index = 10,000 + 1,000 +
Radium index = cRa
200
where CR, CRS and Cjh are the concentrations of potassium-40, radium-226
and thorium-232 expressed in terms of Bq m~3 of building material.
174
-------
70 Bq m-3 (0.02 WL), the maximum permitted level for new development, is
a functional requirement implying that technical measures may be necessary
against all sources of radon gas, for example, radon in the ground, in
building materials and in household water supplies. This regulation
supercedes the proposal from the Radon Commission that, in areas where gamma
radiation in the ground at foundation level exceeds 30 uR/h, houses shall
either be constructed "radon safe" or the site investigated to determine
whether a "radon safe" construction is necessary.
SEARCHES FOR "RADON HOUSES"
Searches for houses with high radon daughter levels have been in progress
since the spring of 1979. Initially the search was aimed at finding houses
constructed with alum shale based aerated concrete, but more recently
attention has been focused on the search for houses where high indoor radon
levels are related to high soil radon concentrations.
The search for houses constructed with radioactive concrete faced certain
problems. As house deeds generally contain no information as to the type of
concrete used, most houses in the country need to be visited in order to
determine whether or not they are constructed of radioactive concrete.
The searches have been the responsibility of the Local Health
Authorities. These authorities have relied upon information from householders
and measurements of gamma radiation using handborne scintillometers or
carborne scintillometer measurements (Wahren et al 1979). The latter method
has proved to be very effective permitting control of radiation from the outer
walls of 600 to 1,000 houses per day.
The carborne measurements carried out by the Geological Survey of Sweden
use a scintillometer with a sodium iodine (Nal) crystal which has a volume of
6,130 cubic centimetres. The instrument is mounted in a car with a shield
against radiation from the ground in order to reduce the background radiation
contribution (Fig. 2). A follow-up program of measurements of indoor radon
daughter levels has commenced for those houses which are judged to have a
problem.
To date (Spring 1981), radon daughter measurements have been performed in
approximately 20,000 houses. Most of the measurements have been made using
alpha-sensitive film. On a more limited scale, measurements have been made
using the filter method or thermo-luminiscence detectors (TLD).
For most of the film measurements, Track Etch films have been used. The
films (2 per house) have been used without radon daughter filters. The
measuring period has generally been 3 months, summers preferably being
avoided. The results of the two measurements for each individual house have
been converted to give an average annual radon daughter concentration
(Samuelson, 1980).
RESULTS OF INDOOR RADON MEASUREMENTS
The first compilation of measurements of radon daughter concentrations
from 5,600 houses built of radioactive aerated concrete gives the following
results: 46% of the houses have levels exceeding 200 Bq m~3 (0.05 WL), 14%
175
-------
Figure 2
176
-------
levels exceeding 400 Bq m~3 (0.11 WL) and 2% levels exceeding 1,000 Bq m 3
(0.27 WL) (Hildingsson, 1981). A more recent compilation for 12,000 houses
gives very similar results: 48% with levels exceeding 200 Bq m~3, 13%
levels exceeding 400 Bq m~3 and 1% levels exceeding 1,000 Bq m~3
(Hildingsson, pers. comm.).
Clear geographical variations in the radon daughter levels are apparent
from the results so far obtained. These variations are caused, either by
variations in the radium content of the aerated concrete used, or by
variations in the soil gas radon concentrations, the latter being closely
related to the geology. Variations in the radium content of the aerated
concrete are due to the fact that this type of concrete was manufactured in
different parts of Sweden using alum shale with widely varying uranium
contents.
There is a marked increase in the number of houses with high indoor radon
levels in areas where the bedrock consists of alum shale or uranium-rich
granites and pegmatites (Table 1). It has been found, however, that sporadic
occurrences of high indoor radon levels also occur in areas with normal
uranium contents in the bedrock or soils. Enchanced soil gas radon levels
have been noted in glacial eskers with normal uranium contents of 3-8 ppm U in
the soil and in areas with scattered occurrences in uranium-rich pegmatites.
The initial results of the program of indoor measurements show clearly
that the problem of radon emanation from the ground is greater than that from
building materials. At a rough estimate, 3,000 - 15,000 houses in Sweden are
in need of remedial measures against radon penetration from the ground.
Tracing these houses will be difficult. One way would be to carry out indoor
measurements in all houses built in areas known to have high uranium contents
in the bedrock or soil cover. Tracing of the sporadic ocurrences is however a
problem. It should also be borne in mind that exceptionally high soil gas
levels exist in houses which are ventilated in such a way that large
quantities of air are drawn into the building through cracks, etc. in the
foundation or cellar walls.
RESEARCH
A research program, initiated by the Radon Commission, is underway to
investigate the relationship between radon concentrations and uranium content
in the ground and indoor radon and gamma ray levels. 100 houses with high
indoor radon daughter levels from areas of alum shale or uranium-rich granite
have been selected for detailed studies of the bedrock, soils, groundwater and
building techniques. These houses are not constructed from radioactive
aerated concrete. The investigations will include in situ determinations of
the U-, Th- and K-content of the rocks and soils using gamma spectrometers,
gamma logging, measurements of the soil gas radon content and/or radon
emanation from the surface, measurement of radon content in the groundwater
and in the drainage layer under the houses, and measurements of radon daughter
levels in the houses. The results of the investigations should be available
in 1982.
Other research programs are also in progress where various types of
remedial measures are being studied, including means of ventilation and the
laying of aluminum foil on the floor to prevent radon penetration from the
ground.
177
-------
Locality
Uppsala
(houses)
Skovde
(houses and
apartments)
Stockholm
suburb
(houses)
Varnhem
(houses)
Lysekil
(houses)
Building Radon daughter levels, Bq m~3, in the investigated Geology
material houses and apartments
% > 200 % > 400 % > 100 no. houses investigated
aerated 3.5 1.0 516 Till, sand, gravel and clay overlying
concrete granodiorite and acid to basic
volcanics (U in bedrock 1-8 ppm)
"- 79 42 9* 380 Sand, clay and alum shale overlying
sandstone, alum shale and limestone
(U in alum shale 50-300 ppm)
"- 65 42 62 278 Till, sand and clay overlying
gneisses younger U-rich granites and
pegmatites (U in gneiss 2-b ppm, in
granites 10-20 ppm). Well exposed.
other type 90 48 22 31 Alum shale rich till, sand and
of b. material gravel overlying sandstone and alum
shale (U in alum shale 50-300 ppm)
"- 20 10 2 63 Uranium-rich granite, exposed (U
content 12-37 ppm)
1 6 houses 4,000 Bq m~3
1 house 8,000 Bq m~3
2 1 house 6,000 Bq m~3
Table 1. Variations in indoor radon daughter levels reflecting the geology.
-------
SITE INVESTIGATIONS
In order to comply with the regulations concerning radon daughter levels
in the new buildings (70 Bq m~3), one needs either to build houses "radon
safe", or to know that the soil gas radon content is so low that no indoor
problem will arise. In the case of building on ground with enhanced radon
concentrations, the type of "radon safe" construction used may be varied
according to the actual soil gas radon levels.
The purpose of the site investigations is to determine whether or not the
soil gas radon concentration within a planned area will give rise to high
indoor levels once the houses are built.
Account must be taken of the changes in the soil gas radon concentrations
which will be caused by the actual process of building, for example, lowering
of the water table or removal of some of the soil cover so that the
foundations lie at a deeper level.
For the site investigations carried out by SGU, soil gas radon
measurements are made at a depth of one metre in order to minimize temporary
fluctuations caused by variations in wind, temperature and precipitation
without increasing the measuring costs to unacceptable levels. In conjunction
with the radon measurements, observations are made on soil types, bedrock
geology, ground water and gamma radiation both above the ground and in the
soil.
The methods used by SGU are ROAC-cups which are filled with activated
charcoal (Hambleton-Jones and Smit, 1980). Track Etch alpha sensitive film
(Gingrich and Fisher, 1976) and emanometers. The measuring time for ROAC-cups
is 5-7 days, and for Track Etch film 3 weeks. These methods were tested
during 1980 in a research project initiated by the Radon Commission (Hesselbom
et al, 1981). Measurements were performed in both granite and alum shale
environments. The ROAC and Track Etch cups gave comparable results, but the
emanometer readings varied, compared with ROAC and Track Etch, from area to
area probably because varying amounts of atmospheric air were pumped into the
instrument. The amount of interference from atmospheric air will depend on
the porosity and permeability of the soil in which the measurements are made.
The advantage of the emanometer method is that it is quick, and it gives an
idea as to whether radon levels in the soil are enhanced or not. Fig. 3 shows
the results of test measurements carried out by SGU in an area of alum shale.
The bedrock along the profile consists of alum shale (U 150 - 300 ppm)
overlain to the west by limestone (U less than 2 ppm). The soil cover is 5-10
metres thick and consists of clay to sandy till, and in the central part of
the profile of clay. The water table lies 2-3 metres above the bedrock
surface. In the western part of the profile the till is comprised of
limestone fragments, alum shale fragments are absent. This also applies to
the upper 4 metres of the till in the eastern part of the profile. Here the
content of alum shale fragments increases successively with depth.
179
-------
ROAC units
1000
500
Figure 3
ROAC (activated charcoal)
100W
sow
50 E
100E
150 E
TRACKS/mm2
6000-
4000'
2000
100W
sow
100 E
150 E
c/tn
600
400
200
EMANOMETER Re 279
» day 1
• day 3
row
sow
150 E
Pl>m
4-
2
SPEKTROMETER
• uranium
100 W
sow
SOE
100 E
150 E
180-p:
170
•* _»-9if>»i:PfiQ-* _ • /^•^»-o->__QVr;-?.-Jf(--i-i>j!Tx?
) «tj U • 'r^C OQ, • • •M«*5W;-X»'O*
150 E
180
-------
The radon measurements show that the radon concentration in the soil for
the western part of the profile is low, approximately 3,000 to 30,000 Bq
m~3. This can be related to the low uranium content of the till combined
with the shielding effect of the limestone horizon, the till cover and the
high water table all of which prevent radon from the alum shale horizon from
reaching the surface. In the eastern part of the profile the shielding effect
is no longer present and the soil gas radon content is approximately 120,000 -
160,000 Bq m~3.
The results show a good correlation between the measurements performed
with ROAC and Track Etch cups and the emanometer.
None of the methods used by SGU are calibrated to give absolute
concentrations of radon in the soil in Becquerels per cubic metre. Track
Etch, however, quote an average value of approximately 6,000 Bq m~3 for all
soil gas radon measurements performed by their method. Of the measurements
carried out by SGU at a depth of one metre in till or gravel containing alum
shale, values some 30 to 300 times larger than the average value quoted by
Track Etch have been obtained. For till or gravel containing fragments of
uranium-rich granite, values 25 to 75 times the average Track Etch value have
been measured. In other words, soil gas radon levels in areas of alum shale
can be as high as approximately 500,000 - 1,800,000 Bq m~3, and in areas of
uranium-rich granites 200,000 - 500,000 Bq m~3. With such high soil gas
radon levels, intake of more than 70 litres per hour of soil air (radon
content 500,000 Bq m~3) into a house with a ventilation rate of 0.5 air
exchanges per hour will be sufficient to produce indoor radon daughter levels
exceeding 70 Bq m~3.
Fig. 4 illustrates an area investigated by SGU in the county of Narke,
central Sweden. The purpose of the investigation was to determine the radon
content in the soil air in an area planned for development. The investigation
included radon measurements using both an emanometer and Track-Etch film,
gamma-radiation measurements with a handborne scintillometer, and
gamma-logging of drill holes.
The bedrock of the area consists of alum shale which is overlain to the
west and north by limestone. The bedrock is covered by till and sand. In the
eastern part of the area, layers of clay occur interbedded in the sand. The
surface of the till lies at 1-3.4 metres depth. In the northern and western
parts of the investigated area, the till is dominated by limestone fragments,
whereas in the southern and eastern part alum shale fragments dominate. The
water table lies at a depth of 0.4-1.1 metres. Tailings of burnt alum shale
(rodfyr) have been tipped in the northern part of the area.
The gamma radiation measurements made at ground level gave low readings of
6-11 yR/H, except for the area with rodfyr where the radioactivity is 90-115
yR/h. The gamma-log results also gave low readings of 3-10 yR/h with a
slight increase to 14-19 yR/h for soils containing a few fragments of alum
shale. It should be noted, however, that the drill holes only penetrated the
upper soil layers down to the upper surface of the till. The readings
therefore do not apply to the radiation levels of the till.
181
-------
N
LEGEND
< 15 000 Bq m3
> 15 000 Bq m3
>100000 Bq m3
High water table
Drill holes
Emanometer measurements
Track-Etch measurements
Investigated area
Planned development
150 M
-------
The radon measurements were made at the greatest possible depth (0.9
metres for Track Etch and 0.7 metres for the emanometer) but the high level of
the water table often prohibited this.
On the basis of the results of the radon measurements, the investigated
area can be subdivided into three (Fig. 4). In the north and northwest where
the till is dominated by limestone fragments, the radon concentration in the
soil gas is normal to slightly raised.
In the southern and eastern parts of the area, where the till is dominated
by alum shale fragments, the soil gas radon level is higher than normal,
30,000 - 100,000 Bq m~3. Within the latter area however, lower values were
obtained where the water table was very near the surface. The high ground
water level hinders the radon gas from the alum shale till from reaching
ground level. If, however, the water table is lowered, either naturally or as
a result of construction work, the content of radon in the soil gas will
increase in these areas. Soil gas radon levels in the areas of tipped rSdfyr
exceed 100,000 Bq m~3.
In the areas with high levels of soil gas radon, the planned dwelling
should be so constructed as to prevent infiltration of radon from the ground
into the dwellings.
183
-------
References
Gingrich, J.E. and Risher, J.C., 1976. Uranium exploration using the Track-
Etch method. IAEA-SM-208/19, 213-225.
Rambleton-Jones, B.B. and Smit, M.C.B., 1980. ROAC - a new dimension in radon
prospecting. Atomic Energy Board, Pretoria, South Africa. ISBN 0 86960
7081, 24 pp.
Hesselbom, A., Israelsson, S. and Tovedal, H., 1981. Radon in the ground. A
study of methods and instruments for determining radon concentrations in
the ground. Byggforskningsradet, Report R47:1981 (in Swedish), 75 pp.
Hildingsson, 0., 1971. Radon daughter levels in 5,600 houses. Measurements
made using alpha sensitive film and filter method. Technical Report,
Statens Provningsanstalt, SP Rapp. 1981:27, (in Swedish).
Hultqvist, B. 1956. Studies on naturally occurring ionizing radiations with
special reference to radiation doses in Swedish houses of various types.
Svenska vetenskapsakademins handlingar, fjarde serien, Band 6, nr 3,
Stockholm, Sweden.
Radonutredningen, 1979. Preliminary proposal for measures against radiation
hazards in buildings. Report from the Radon Commission, Jordbruksdeparte-
mentet, Ds Jo 1979:9 (in Swedish), 114 pp.
Samuelson, I. 1980. Determination of the annual average radon daughter con-
centration in a house measured with alpha sensitive films. Statens
Provningsanstalt, SP A2 601, 8 pp.
Socialstyrelsen, 1980. Statement from the National Board of Health and Welfare
with advise and regulations concerning remedial measures against radon in
dwellings, September 1, 1980. Socalstyrelsens forfattningssamling, SOSFS
(M) 1980:71, 4 pp, (in Swedish).
Statens Planverk, 1980. Svensk Byggnorm 1980 (Swedish Building Code 1980).
Statens planverks forfattningssamling 1980:1 (in Swedish).
Swedjemark, G.A., 1977. The ionizing radiation in dwellings related to the
building materials. Statens stralskyddsinstitut. Report 381:1977-004, 1-9.
1978a. Radon in dwellings in Sweden. In Proceedings from the Symposium
on Natural Radiation Environment III, Houston, Texas, April 23-28, 1978.
1978b. The effects of energy saving reduced ventilation on radiation dose
in dwellings. Statens stralskyddsinstitut, Report SSI:1978-014, 1-13 (in
Swedish).
1980. Radioactivity in houses built of aerated concrete based on alum
shale. Statens stralskyddsinstitut, Report SSI:1980-14, 1-6.
184
-------
Swedjemark, G.A., Hakansson, B. and Hagberg, N., 1979. Radiation levels in
houses built on wastes from processing of alum shale. Statens
stralskyddsinstitut, Report 531:1979-006, 1-43 (in Swedish).
Wahren, H., Makitalo, A., Persson. T. and Svensson, C.-E, 1979. An attempt to
trace 'radon houses' in the municipality of Uppsala. Delrapport 1979,
Lanslakarorganisationen i Uppsala Ian, 62 p, (in Swedish).
Wilson, C., in press. Regional environmental documentation of natural radia-
tion in Sweden.
185
-------
Appendix: Summary of provisional regulations and
recommenda.tions concerning radiation hazards in buildings in Sweden
1. Directions issued by the National Board of Health and Welfare, in force
from September, 1980.
A building is regarded as insanitary when the radon daughter concentration
in rooms in continual use exceeds an annual average of 400 Bq m~3.
SOSFS(M) 1980:71 (Socialstyrelsen 1980).
2. Mandatory regulations issued by the National Board of Urban Planning,
SWEDISH BUILDING CODE (SEN) 1980, in force from January 1, 1980. National
Board of Urban Planning Statute Books 1980:1 (Statens planverk 1980).
New buildings
Buildings shall be so constructed that the annual average concentration of
radon daughters in rooms in continual use shall not exceed 70 Bq m~3.
The annual average concentration of radon daughters is determined
according to methods laid down by the National Board of Urban Planning in
consultation with the National Institute of Radiation Protection.
SEN 36:41
The regulation relating to a maximum permitted indoor radon daughter
concentration of 70 Bq m~3, according to 36:41, can require the application
of remedial measures against sources of radon in the ground, in household
water supplies and in building material.
SEN 31:142
A building shall be so constructed that gamma radiation in rooms in
continual use shall not exceed 50 yR/h.
SEN 31:141
A satisfactory level for gamma radiation is achieved if the regulation
relating to building materials, 31:143, is applied, and if gamma radiation
from the ground is screened by a concrete structure or filling of low
radioactive material.
SEN 31:1411
186
-------
Rebuilding
Buildings shall be so constructed that the annual average concentration of
radon daughters in rooms in continual use shall not exceed 200 Bq m~3-
Exception is made where the radon daughter concentration cannot be brought
below this level by means of increased ventilation and remedial measures
according to 31 rebuilding: 14.
SEN 36: Rebuilding: 41
Exception to the regulation quoted in SEN 31:141 may be granted. (That is
to say, there are no regulations which apply to lowering of gamma radiation
levels in cases of rebuilding.)
SEN 31: Rebuilding: 141
Exception to the regulation quoted in SEN 31:143 regarding existing
building materials, may be granted. However, an accessible, strongly radon
emanating filling material shall be removed where required in order to conform
with the regulation concerning radon daughter concentrations quoted in SEN 36
Rebuilding: 41.
Easily accessible filling may be found against cellar walls, and in the
framing of joists and the crawl space.
SEN 31: Rebuilding: 143
Building materials
Building materials used in buildings in continual use shall not have gamma
or radium indexes exceeding 1.0.
SEN 31: 143
Filling materials and material used in the drainage layer under the
foundations also come under the heading building materials.
SEN 31: 1431
Gamma- and radium indexes are defined as follows:
CK CRa
Gamma index = 10,000 + 1,000
Radium index =
where CR, CRa and C-pn are the concentrations of potassium-40, radium-226
and thorium-232 expressed as Bq kg"1 of bulding material.
Out of doors
There are no regulations which apply to gamma radiation levels out of
doors. However, it is recommended that in areas which are in regular use, for
example playgrounds, gamma radiation should not exceed 100 yR/h.
187
-------
Figure Captions
1. Distribution of the alum shale formation and of areas known to contain
radioactive granites.
2. Car and equipment used in the search for houses with aerated concrete.
3. Results of test measurements made in an area of alum shale (after
Hesselbom et al 1981).
4. Map showing the results of radon measurements in an area planned for
development.
188
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EFFECT OF AIR CIRCULATION
AND DUST REMOVAL ON INDOOR
RADON DECAY PRODUCT CONCENTRATION
S.N. Rudnick, W.C. Hinds, E.F. Maher,
J.M. Price, and M.W. First
Department of Environmental Health Sciences
Harvard University
School of Public Health
665 Huntington Avenue
Boston, Massachusetts 02115
ABSTRACT
The effectiveness of increased room air motion and dust removal in
reducing working levels in residences subject to radon intrusion was evaluated
in a 90-m3 chamber under steady-state conditions for air infiltration rates
between 0.2 and 0.8/hr. Room-sized electrostatic precipitators and high-effi-
ciency fibrous filters were tested as typical residential air cleaning
devices; a portable box fan and a ceiling fan were employed as typical resi-
dential air movers. Reductions in working levels from 40 to 90% were mea-
sured. The fate of radon decay products was determined by direct measure-
ment. When mixing fans were used, most of the potential alpha energy deposit-
ed was plated out on the room surfaces; less than 5% was deposited on the fan
blades. Results were compared to a mathematical model based on well-mixed
room and good agreement was obtained.
INTRODUCTION
Strategies to control radon decay products in residences can be divided
into three types: (1) prevention of radon entry into homes (e.g., caulking,
sealing, barrier paints, and judicious selection of building materials); (2)
dilution of outside air directly or through heat exchangers; (3) removal of
radon or radon decay products from indoor atmosphere by various air treat-
ments. Historically, strategy (2) has been most widely used, perhaps
inadvertently. In recent years, it has become less acceptable because of the
high cost of energy for space heating and cooling.
The present study was directed to strategy (3) , although no attempt was
made to cleanse the air of radon gas. The treatment methods evaluated
included the use of room-sized electrostatic precipitators, high-efficiency
189
-------
air filters, and air mixing by fans. Because much of the data collected has
not been analyzed, this paper should be considered a first reporting of on-go-
ing research. More complete results will be available in three months.(1)
Very little has been published on the use of methods to remove airborne
radon decay products. The experimental work that has been reported, concerned
primarily with the reduction in radon decay product concentrations in
mines, (2~8) has only limited application to control in residences because
of the higher dust concentration, higher air infiltration rates, and higher
humidity found in mines.
EXPERIMENTAL PROCEDURES
Experimental studies were conducted in a 90-m-^ chamber, about the size
of a large room in a house. Special attention was given to making this
chamber as much like a residence as possible, although certain differences are
noteworthy. The chamber's 4-m high ceiling is not characteristic of houses,
nor are its painted metal walls. We do not believe, though, that these
differences are important. Transient effects in houses, such as changes in
air infiltration or radon intrusion rates with time, however, are undoubtedly
important, but we made no attempt to simulate this behavior. In fact, to
facilitate interpretation of our experimental results, we held all parameters
within our control constant, and no data were retained for analysis until
steady-state conditions had been reached.
Air Infiltration
The natural air infiltration rate into our experimental chamber was very
low; from the decay rate of a CO tracer gas,(l) we measured about 0.015/hr.
Because we wanted to hold the air infiltration rate constant at various sett-
ings and still simulate air infiltration into a room of a house, a blower was
installed outside the chamber to exhaust air from it. (See Figure 1.) No
inlet air port was provided and, thus, incoming air was forced to infiltrate
through the cracks and pores in the walls or the seals around the door and
windows. Pressure in the chamber was never more than 3-mm Hg below barometric
pressure and was usually less. The exhaust airflow rate was measured with a
calibrated venturi flowmeter, and the rate controlled with a butterfly
damper. The air infiltration rate was equal to the measured airflow rate
divided by the chamber volume. The particulate level and size distribution of
the infiltrating air was about the same as laboratory air, although somewhat
variable, and is reported elsewhere.(1)
Radon Generation
Radon-222 gas was generated by de-emanation of a 100-|iCi solution of
Ra-226. About 0.2 L/min of prehumidified air flowed continuously through a
bubbler containing the radium solution, through a liquid carryover trap and
membrane filter, and into a distribution manifold placed on the floor of the
chamber to simulate radon emanating from the subsoil and entering through the
floor- This is shown schematically in Figure 1. The manifold was constructed
from 3.5-cm I.D. plastic pipe in which 0.6-mm holes were drilled. Inasmuch as
the holes are much smaller than the pipe diameter, gas is evenly discharged
190
-------
from all holes. These holes face downward and are located on 60-cm centers
throughout the chamber. About 5 L/min of dilution air was also introduced
into the distribution manifold.
Sampling and Measurement of Radon Decay Products
As shown in Figure 1, sampling ports were provided in the exhaust duct and
on one wall of the chamber. Both ports accept 50-mm diameter open-faced
filter holders, which minimize aerosol sampling losses. To determine whether
these samples would be representative of the contents of the chamber, we made
tests in which a tracer gas (CO) was introduced continuously through the dis-
tribution manifold. After steady state had been reached, samples were taken
from the two sampling ports as well as from eight other locations at various
heights in the chamber. All samples were in reasonably good agreement over
the range of air infiltration rates we studied.CD Further verification
that the chamber was well mixed can be made from a comparison of samples taken
from the exhaust duct and wall port. For 25 pairs of samples, the exhaust
duct gave an average of 0.0907 working level (WL) compared to 0.0890 WL from
the wall port, about a 27, difference.
Filter samples were counted by alpha scintillating using disposable
Ag-activated ZnS phosphors coated on one side of a Mylar film (William B.
Johnson & Associates, Inc., Research Park, Montville, New Jersey 07045),
which were placed in direct contact with a bare photomultiplier tube and
enclosed in a light-tight box. Working level was determined by the modified
Tsivoglou method.C9)
MODELING
Because samples taken from various locations in the experimental chamber
showed good agreement, we believe that a material balance for radon decay
products using a steady-state, well-mixed model should give reasonable predic-
tions of working level. When incoming air is essentially free of radon or its
decay products, as was found for our experiments, the following equation is
obtained: CD
WL =
(Xr + I)(xa + I + R)
CD
where WL = potential a-energy concentration of short-lived radon decay
products in air in units of working level
S = radon exhalation rate per room volume in Bq/(hr*nP-'
I = air infiltration rate in 1/hr
X = radioactive decay constant (Xr = 0.00758/hr,
Xa = 13.7/hr, Xb = 1.55/hr, and Xc = 2.11/hr)
= dimensional conversion factors (3.79 X 10~
2.13 X 10~4» respectively)
= removal rate for particulate matter; 1/hr.
and
191
-------
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r >
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C3+- Radon Generator
t
*>
^
f
\
s
\.
f
\
f
\
^ Exhaust Ventilation ^ ^ s.mp|,nfl Port (2*
(2.6 ft. above floor) ft abov. f|oof)
I
To
Exhaust
•Sampling Port
Venturl Flowmeter
Butterfly
Valve
FIGURE 1: SCHEMATIC DRAWING OF EXPERIMENTAL CHAMBER
-------
R can be subdivided into various particulate removal mechanisms, i.e.,
R = Pn + Pf + A (2)
where Pn= rate of plateout due to normal air motion (including that
caused by air infiltration)
Pf= rate of plateout due to forced convection (e.g., from mixing
fans)
A = air cleaning rate (e.g., from filters and electrostatic
precipitators)
These terms are not necessarily independent. For example, a filter may remove
particles, while its fan enhances plateout.
RESULTS
Experimental protocol was the same for all runs. The air infiltration
rate was set, and, after the contents of the chamber were allowed to come to
steady-state conditions, various measurements were made, some of which will be
reported at a later time.(1) Whenever possible, the data obtained were
compared to predicted concentrations from Equations (1) and (2) .
Effect of Air Infiltration Rate
A log-log plot of the experimentally measured working level versus air
infiltration rate is shown in Figure 2. (The solid line is the linear regres-
sion line.) Also shown are predicted values from Equation (1) when only
plateout due to normal air motion is considered. The data follow the general
slope of these lines, and a plateout rate of between 0.25 and 0.50/hr can be
inferred. (A background plateout rate of 0.4/hr was assumed when the model
was used for prediction in other sections of this paper.) Verification of
these results by direct measurements of potential alpha energy on the surfaces
of the chamber were made and will be discussed later.
Effect of Forced Convection
The effect of various mixing fans is shown in Figure 3, a plot of working
level fraction remaining after a fan was started versus air infiltration
rate. Reductions in WL varied from about 40 to 80%. Based on Equations (1)
and (2) , predicted values of WL fraction remaining versus air infiltration
rate, with rate of plateout due to forced convection as a parameter, are also
shown in Figure 3. From this plot, a rate of plateout due to the fans of
between about 2 and 5/hr can be inferred. (This plateout rate is in addition
to that obtained from normal air motion.) The data also show a greater reduc-
tion in WL at lower air infiltration rate, although the reason for this is not
clear.
Manufacturer's specifications for these fans are given in Table I.
193
-------
ID
>
HI
_l
O
DC
O
0.5 r
0.2 -
0.1 -
0.05 -
0.1
Regression line for
experimental data
RATE, hr-1
Well-mixed model:
Eqs. (1) and (2).
0.2
0.5
AIR INFILTRATION RATE, hr-1
FIGURE 2: WORKING LEVEL; AIR INFILTRATION
RATE WITH NO AIR TREATMENT.
194
-------
Ul
o
z
z 1.0
HI
QC
o
I-
o
QC
LU
>
LJJ
_l
O
DC
O
0.5
Regression line for
experimental data
FORCED
PLATEOUT
RATE, hr-1
Well-mixed model: Eqs.
(1) and (2). (Adjusted
for normal plateout rate
of 0.4/hr.)
20-in. BOX FAN
A LOW SPEED
QHIGH SPEED
O 52-in. CEILING FAN (high speed)
0.5
1.0
AIR INFILTRATION RATE, hr-1
FIGURE 3: EFFECT OF MIXING FANS ON WORKING LEVEL
-------
TABLE I:
MANUFACTURER'S SPECIFICATIONS FOR MIXING FANS
Hunter 20-in box fan
(Model 11077)
Hunter 52-in ceiling fan
(Model 22306-7J)
Speed
High
Medium
Low
High
Low
cfm
(NEMA Method)
5500
5200
4800
7000
4000
RPM
1000
930
750
200
115
Watts
• —
185
150
100
155
80
Although the box and ceiling fans gave comparable reductions in WL, the ceil-
ing fan has significant advantages: it consumes less energy than the box fan,
is considerably quieter, is designed to operate continuously, and produces
less noticeable air motion. It also can be used all year round; the manu-
facturer(lO) claims it "reduces air conditioning cost during the cooling
season and reduces wasteful heat stratification during the heating season."
Effect of Particulate Air Cleaners
Figure 4, a plot of WL fraction remaining versus air infiltration rate,
shows the effect of various particulate-removing air cleaners. Predicted WL
fractions remaining versus air infiltration rate with air cleaning rate as a
parameter are also shown. (A background plateout rate of 0.4/hr was assumed.)
The electrostatic precipitators (Sears Model No. 156.73300 Console Air
Cleaner), which we measured to give an air throughput rate of 5/hr for our
chamber, yielded WL reductions that were in excellent agreement with the
predicted values, although they assume 100% collection efficiency. About half
of this reduction was obtained with the high voltage turned off. Whether this
latter reduction was due to removal by the unit's fan and charcoal filter or
by enhanced plateout on the walls is not known.
A high-efficiency particulate air (HEPA) filter, which removes essentially
all particulate matter, was also tested at an air throughput rate of 5/hr. It
yielded an effect equivalent to between 10 and 20/hr- This difference can be
attributed to increased plateout. Removal of particles from the air would
increase the fraction of radon decay products that are unattached to particles
and thus significantly enhance plateout; air motion caused by the HEPA's
blower would also promote plateout. We noted other indications of this pheno-
menon: limited data on the unattached fraction(l) indicated that about 80%
of the working level was unattached, whereas only about 20% was unattached for
most other runs. Extreme disequilibrium, another indication of high unattach-
ed fraction, was also observed.
196
-------
O
I 1.0
2E
ID
CC
z
g
i-
o
QC
LLJ
>
LU
QC
O
0.5
Regression line
for experimental data
PARTICULATE
AIR CLEANING
RATE, hr-1
1
-2
Well-mixed model:
Eqs. (1) and (2)
(adjusted for normal
plateout rate of 0.4/hr)
D NORMAL OPERATION
• NO HIGH VOLTAGE
ELECTROSTATIC
PRECIPITATOR (6.0/hr)
A 1.1/hr
O 6.0/hr
HEPA FILTER
0.5
AIR INFILTRATION RATE, hr-i
1.0
FIGURE 4: EFFECT OF PARTICULATE AIR CLEANERS ON WORKING LEVEL
-------
DIRECT PLATEOUT MEASUREMENTS
Paper or aluminum-foil disks, affixed to various locations on the surfaces
of the chamber, were removed from the chamber and counted sequentially by
alpha spectrometry. The fan blades were also removed from the chamber and
selected areas counted simultaneously by direct contact with six ZnS alpha
scintillation counters, which were protected from room light by thin aluminiz-
ed mylar windows. Counting was done over two time periods for alpha spectro-
metry and three time periods for scintillation, and the potential alpha-energy
areal density (MeV/m2) was back-calculated to the time at which the samples
were removed from the chamber.^'
The results of a material balance on potential alpha-energy for five runs
are given in Table II. Contributions from the air, chamber surfaces, and fan
blades and housing were summed and compared to the predicted values from
Equation (1); between 69% and 97% of the predicted potential energy was
accounted for.
Greater than 95% of the plateout was found to take place on the chamber
surfaces. Holub et al.^°' found deposition on fan blades, but none on walls
for similar experiments. The reasons for these conflicting results may be due
to differences in measuring technique. In our experiments, less than 5% of
the potential alpha-energy lost from the air was found on the fan blades,
which had only 0.4% of the surface area of the chamber. Thus, the potential
alpha-energy areal density on the fan blades was greater than 10 times that on
the walls. This might explain why the relative external activity on the fan
blades measured by Holub et al.'s beta-gamma detection system was in a measur-
able range, whereas the wall activity was not detectable by their equipment.
Other differences between Holub et al.'s and our experiment, such as aerosol
size and concentration, chamber surface to volume ratio, and infiltration air
sources, make comparison difficult.
CONCLUSIONS
Various methods may be used to reduce working levels in residences. A
ceiling fan, for example, was shown to give up to 75% reduction in working
level. Because it was most effective at low air infiltration rates, it is
probably a good choice for an energy-efficient house. It consumes about 150 W
of power and may also reduce cooling and heating requirements. Greater reduc-
tions are possible using HEPA filters, but higher energy consumption and noise
may prove to be a deterrent to their use. Higher fractions of unattached
radon decay products found when HEPA filters were used may be less desirable
from a health-effects standpoint, as the increased hazard commonly believed to
be associated with unattached radon decay product may offset some of the
benefits of lower working levels.
ACKNOWLEDGEMENTS
This work was supported by the U.S. Environmental Protection Agency Con-
tract No. 68-01-6250.
198
-------
TABLE II
In-Chamber
Air Treatment
None
None
132-cm ceiling
fan (high speed)
132-cm ceiling
fan (high speed)
Two 51-cm box
fans (high speed)
AIR
Infiltration
Rate, Hr"1
0.20
0.45
0.20
0.45
0.45
MATERIAL
Predicted3.
Potential
a-Energy
(Total)
3.97x109
(100%)
1.52x109
(100%)
3.97x109
(100%)
1.52x109
(100%)
1.52x109
(100%)
BALANCE ON POTENTIAL ALPHA ENERGIES IN
MeVl
EXPERIMENTAL MEASUREMENTS
AIR
2.972x10^
(74.9%)
1.289x109
(84.8%)
8.284x10^
(20.9%)
5.768xl08
(37.9%)
4.56xl08
(30%)
CHAMBER
SURFACES
5.043xl08
(12.7%)
1.802x108
(11.8%)
2.641x109
(66.6%)
7.570x108
(49.8%)
5.265xl08
(34.6%)
FAN FAN
BLADES BOX
8.109xlOb
(.02%)£
9.36x10^
(0.1%)£
1.006x108
(2.5%)
3.861x107
U.5%)
4.095xl07 2.808x10?
(2.7%; (2%)
Found
Predicted
87.8%
96.7%
89 . 9%
90 . 2%
69.3%
Predicted potential alpha energy based on a well-mixed model, de-emanation of lOO-yCi Ra-226 into a
90-nP chamber, no plateout, and radon-free infiltration air.
% of the predicted total potential alpha energy is shown in parentheses.
On still blades of 132-cm ceiling fan.
-------
References
1. Rudnick, S.N., Hinds, W.C., Leith, D., First, M.W., Maher, E., and Price,
J., "Effect of Indoor Air Circulation Systems on Radon Decay Product
Concentration," Final Report under EPA Contract 68-01-6250 (in prepara-
tion) .
2. Goodwin, A., "Review of Problems and Techniques for Removal of Radon and
Radon Daughter Products from Mine Atmospheres," in Proceedings of the
12th AEG Air Cleaning Conference, CONF-720823, NTIS, Springfield, VA,
1973, pp. 378-398.
3. Coleman, R.D., Kuznetz, H.L., Woolrich, P.F., and Holaday, D.A., "Radon
and Radon Daughter Hazards in Mine Atmospheres," Ind. Hyg. Quart. 17;405
(1956).
4. Shreve, J.D., and Cleveland, J.E., "Effects of Depressing Attachment
Ration of Radon Daughters in Uranium Mine Atomosphere," Am. Ind. Hyg.
Assoc. J. 33:304 (1972).
5. Rock, R.L., "Control of Radon Daughters in U.S. Underground Uranium
Mines," in Proceedings of the 12th AEC Air Cleaning Conference,
CONF-720823, NTIS, Springfield, VA, 1973, pp. 348-354.
6. Washington, R.A., Chi, W., and Regan, R., "The Use of Vermiculite to
Control Dust and Radon Daughters in Underground Uranium Mine Air," in
Proceedings of the 12th AEC Air Cleaning Conference, NTIS, Springfield,
VA, 1973, pp. 355-376.
7. Wrenn, M.E., Eisenbud, M., Costa-Ribeiro, C., Hazle, A.J., and Siek,
R.D., "Reduction of Radon Daughter Concentrations in Mines by Rapid
Mixing Without Makeup Air," Health Phys. r7:405 (1969).
8. Holub, R.F., Droullard, R.F., Ho, W., Hopke, P.K., Parsley R., and
Stukel, J.J., "The Reduction of Airborne Radon Daughter Concentration by
Plateout on an Air Mixing Fan," Health Phys. _36:497 (1979).
9. Thomas, J.W., "Measurement of Radon Daughters in Air," Health Phys.
22_:783 (1972).
10. Robins & Myers, Inc., manufacterer's literature provided to retailers.
200
-------
SOME MEASUREMENTS OF THE EQUILIBRIUM
FACTOR FOR RADON DAUGHTERS IN HOUSES*
R.E. Toohey, M.A. Essling, H. Wang+ and J. Rundo
Radiological and Environmental Research Division
Argonne National Laboratory
Argonne, Illinois 60439
ABSTRACT
The problem of relating radon levels in houses to the radiation doses
received by their residents would be greatly simplified if the parameters
which determine the equilibrium factor, or working level ratio, could be
identified and their effects predicted. The first step in such a program is
to measure the equilibrium factor in a number of houses under a variety of
conditions, by simultaneously measuring both the radon concentration and the
working level.
Our preliminary measurements in a few houses indicate that the equilibrium
factor normally varies over a range of 0.05 to 0.50, but on occasions it
approaches 1.0. The mean of eight sets of observations was 0.2O +_ O.14 (one
std. dev.). Some of the parameters which have been observed to affect the
equilibrium factor include the relative areas of room surfaces and airborne
particles, the ventilation rate, and the air circulation. Human activities,
such as cooking and smoking, also affect the equilibrium factor, by directly
affecting the aforementioned variables.
INTRODUCTION
Because the radiation dose to the lung from environmental radon is due
almost entirely to the inhalation of the short-lived daughter products,
measurements of radon levels alone are not sufficient to determine the dose.
Typically the activities of the daughter products in air are not in equilibri-
um with the parent radon, nor is there equilibrium among the daughters them-
selves. The working level (WL) was introduced as a convenient unit to over-
come this problem in uranium mines and it is also applicable to other environ-
ments where radiation dosimetry is the principal concern. It is defined as
that concentration of short-lived radon daughters in any combination which has
a potential alpha-particle energy of 1.3 x 10^ MeV per liter of air. Since
*Work supported by U.S. Department of Energy under contract IW-31-109-ENG-38.
+Visiting Scientist from the North China Institute of Radiation Protection,
Taiyuan, Shanxi, PRC.
201
-------
this is equal to the potential alpha-particle energy of 100 pCi/1 of radon
with all its short-lived daughters in equilibrium, we can define the equili-
brium factor, F, as one hundred times the working level divided by the radon
concentration in pCi/1. Since it is easier to determine the radon concentra-
tion than the working level, the task of determining lung doses would be
simplified if those factors which determine F could be identified and their
effects quantified. In order to do this, simultaneous measurements of radon
concentrations and working levels must be made in houses under a variety of
conditions. In addition, parameters which may affect the equilibrium factor,
such as aerosol concentration and ventilation rate, must also be identified
and monitored. Although the effects of such parameters may be best determined
under controlled conditions in a laboratory, the results must be validated by
measurements in houses.
MEASUREMENTS OF F
Radon levels were determined by either collecting air samples in Lucas
flasks (Lu57), or by continuous monitoring with a Spitz-Wrenn chamber (Wr75).
Concentrations of radon daughters were determined and working levels computed
with an Environmental Working Level Monitor (Ke78). Measurements were made in
three houses owned and occupied by ANL employees; two of the three (H-01,
H-23) have radon levels which routinely exceed 370 Bq/m3 (10 pCi/1). The
radon levels in the third (H-02) ranged from 11 to 300 Bq/m3 (0.3 - 8.0
pCi/1). The results are shown in Table 1.
Values for F reported by other workers have averaged around 0.5 (Ge78,
McGSO). Only one of our series of observations approached this value, while
the mean of all our observations is 0.20 •+ 0.14 (one std. dev.). The radon
concentration (Spitz-Wrenn chamber), working level (EWLM), and equilibrium
factor in the basement of house 23 during the period 27-30 Sep are shown in
Fig. 1. Note that while the radon concentration and working level undergo
diurnal variations by a factor of four, 88% (71/81) of the values of F lie
within the range 0.15 - 0.30. However, some of the variability in F may be an
artifact of the measurement techniques. The EWLM determines working level on
the basis of a three-minute sample of air, whereas the values obtained with
the Spitz-Wrenn chamber were averages of 60-minute counts; furthermore, there
is a delay between a change in the radon concentration outside the chamber and
equilibration inside it, and another delay before the electrostatically col-
lected daughter products are at equilibrium with the radon producing them.
Although the variations in values of F have not as yet been firmly linked
to such parameters as air exchange rate or airborne particle concentrations,
we have observed the lowest values of F when the fan of the heating or cooling
system is in operation. Presumably this removes dust particles from the air
by filtration and impaction, giving unattached daughter products the chance to
be removed from the air by deposition on surfaces within the house.
MEASUREMENTS OF SURFACE DEPOSITION
Laboratory experiments have shown that radon daughters "plate out," i.e.,
deposit on various surfaces exposed to a radon-containing atmosphere (Ho79,
Ge81). We have recently performed some direct measurements of radon daughter
plate out on surfaces in a house. The data are shown in Fig. 2. When the
cover was removed from the window (316 cm2) of a gas-flow proportional
202
-------
counter, the counting rate immediately increased, presumably due to the detec-
tion of the decay of radon and daughters in the air within a-particle range
of the counter (about 4 cm). The counting rate then continued to increase,
showing the characteristic build-up of activity due to deposition of radon
daughters on the surface of the window, until an equilibrium was reached.
When the cover was replaced, the counting rate doubled, because radon
daughters were also deposited on the surface of the cover itself, and then
decreased at a rate characteristic of a mixture of radon daughters.
SUMMARY
Simultaneous measurements of radon levels and working levels in a few
houses have resulted in a mean value for the equilibrium factor of 0.20 _+
0.14. The lowest values of F were observed during the operation of the fan of
a house's heating or cooling system, which presumably removed radon daughters
from the air by both filtration and impaction on walls and other surfaces.
Direct observations of the plate out of radon daughters on surfaces in a house
were performed, confirming the results of laboratory experiments by other
workers.
203
-------
References
Ge80 A.C. George and A.J. Breslin, 1980, The distribution of ambient radon
and radon daughters in residential buildings in the New Jersey-New York
area, in Natural Radiation Environment III, T.F. Gesell and W.M. Lowder,
Eds., U.S. Department of Energy Symposium Series No. 51, CONF-780422,
Vol. 2, p. 1272.
Ge81 A.C. George and E.G. Knutson, 1981, Measurements of radon daughter
plateout, presented at the 26th Annual Meeting of the Health Physics
Society, Louisville, KY, June 21-25, 1981, Abstract No. P/189.
Ho79 R.F. Holub, R.F. Droullard, W. Ho, P.K. Hopke, R. Parde, and J.J.
Stukel, 1979, The reduction of airborne radon daughter concentration by
plateout on an air mixing fan, Health Phys. 36, 497.
Ke78 D.J. Kefe, W.P. McDowell, an P.G. Groer, 1978, The environmental working
level monitor, Final Report to U.S. Environmental Protection Agency,
Argonne National Laboratory Report #P7628C.
Lu57 H.F. Lucas, Jr., 1957, Improved low-level alpha-scintillation counter
for radon, Rev. Sci. Inst. 28, 680.
McG80 R.G. McGregor, P. Vasudew, E.G. Letourneau, R.S. McCullough, F.A.
Prantl, and H. Taniguchi, 1980, Background concentrations of radon and
radon daughters in Canadian homes, Health Phys. 39, 285.
Wr75 M.E. Wrenn, H. Spitz, and N. Cohen, 1975, Design of a continuous
digital-output environmental radon monitor, IEEE Trans. Nucl. Sci.
NS-22, 645.
The submitted manuscript has been authored by
a contractor of the U.S. Government under con-
tract No. W-31-109-ENG-38. Accordingly, the
U.S. Government retains a nonexclusive, royal-
ty-free license to publish or reproduce the
published form of this contribution, or allow
others to do so, for U.S. Government purposes.
204
-------
Table I. Observed values for the equilibrium factor, F.
House
H-01
H-01
H-01
H-01
H-02
H-23
H-23
H-23
Location
2nd
2nd
2nd
2nd
1st
floor
floor
floor
floor
floor
Basement
1st
1st
floor
floor
Period No. Observations
28-31
25-30
15-16
1-6
17-21
26-30
14-15
7-9
Jul
Aug
Feb
Mar
Aug
Sep
Oct
Jan
7
9
28
93
11
81
23
57
0.
0.
0.
0.
0.
0.
0.
0.
Mean
48
16
07
09
31
22
13
12
+
+
+
+
+
+
+
+
F
0.21
0.11
0.04
0.03
0.13
0.06
0.02
0.03
Range of F
0.19
0.02
0.03
0.04
0.12
0.11
0.08
0.06
- 0.83
- 0.35
- 0.20
- 0.23
-0.60
- 0.44
- 0.16
- 0.21
205
-------
FIGURES
Fig. 1. The radon concentration, working level, and equilibrium factor in the
basement of house no. H-23 for a period of four days.
Fig. 2. The build-up and decay of radon daughters on the window of a large-
area proportional counter placed in the utility room of house no.
H-01.
206
-------
K)
o
cn
o
ID"2
Rn
-•"•X-
^ t
WL
« •
102
o
cu
o
o
o
c.
OC
IO1
0.5
0.14
o
-£ 0.3
a
$ 0.2
u-
0.1
0
• «S
• •••*•••
•••••
• • .• •
»«u
••
•.
V. .
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26
27
28
September
Figure 1
29
30
-------
Figure 2
250
200
-------
REGIONAL ENVIRONMENTAL DOCUMENTATION OF
NATURAL RADIATION IN SWEDEN
Carole Wilson
Geological Survey of Sweden
Box 801
S-951 28 Lulea, SWEDEN
ABSTRACT
In 1979, when the problem of high radon daughter levels in Swedish houses
became widely publicized, the need for information on variations in the natur-
al radiation environment became very apparent. The radon problem was at first
attributed to radon emanation from alum shale based aerated concrete, but it
was soon obvious that ground with an abnormally high uranium content consti-
tutes an even greater risk for high radon and radon daughter levels in
houses. The Geological Survey of Sweden was commissioned to produce a docu-
mentation in map form of all areas and rock types with gamma ray levels
exceeding 30 yR/h, with the intention of delimiting risk areas for high soil
gas radon contents.
The maps, known as GEO-radiation maps, are produced at the scale of 1:5O
OOO. They are based primarily upon airborne radiometric surveys, ground
measurements of gamma radiation and geological mapping. To date some 450 map
sheets have been published covering approximately 55% of the country. The
maps provide primary information to local planning, health and building
authorities as to variations in the natural radiation environment. Within the
so-called risk areas marked on the maps, local authorities are recommended to
investigate the soil gas radon content prior to any new development.
Geological environments known, in Sweden, to be associated with radon
daughter problems in dwellings are alum shale, a Cambrian, uranium-rich black
shale, uranium-rich granites and uranium-rich pegmatites. Both alum shale and
uranium-rich granites constitute extensive areas of bedrock.
INTRODUCTION
In 1978, the National Institute for Radiation Protection measured radon
daughter levels in a number of houses built on uranium-rich shale tailings
(Swedjemark et al. 1979). The measured levels exceeded the maximum level of
1110 Bq m~3 (Becquerel per cubic metre) of radon in equilibrium with radon
daughters permitted in Swedish mines. This was the first proof in Sweden that
radon emanating from the ground can give rise to such high concentrations of
radon daughters in dwellings. Earlier, the radon problem in houses was
209
-------
attributed to radon emanation from building materials containing unusually
large amounts of radium, for example, alum shale based aerated concrete
(Swedjemark 1978a, 1979b, 1980),
Early in 1979, a Government Commission, termed the Radon Commission, was
set up to investigate the problem of radiation risks in dwellings (Radon-
utredningen, 1979). At an early stage in the Commissions work, it became
apparent that radon emanating from the ground could constitute as great, if
not greater problem than radon emanation from building materials. Measurement
programs carried out by Local Health Authorities during the last year have
proved this to be true» In Sweden, areas with particular risk for high soil
gas radon contents are considered to be those with a. bedrock of uranium-rich
alum shale (a Cambrian, black shale), uranium-rich granite or uranium-rich
pegmatites and areas of glacial drift cover comprised largely of these rock
types. Knowledge of the geographical distribution of these areas became thus
necessary in order, at least, to prevent future building without the use of
necessary technical measures against radon penetration from the ground.
NATURAL RADIATION ENVIRONMENT
The source of natural radiation from the ground is almost entirely related
to the presence in the bedrock or drift cover of the radioactive elements
uranium and thorium, and their daughter products including radon, and potas-
sium-40. Their concentrations in various rock types in Sweden is very vari-
able. (Table 1).
The geographical distribution of the uranium-rich alum shale formation
(Fig. 1) is fairly well-known due to mapping and prospecting activities, the
latter owing to the rocks' unusually high contents of uranium, vanadium,
molybdenum and organic matter. The uranium content can range from 50 - 350
ppm (Armands 1972: Andersson et al. in press).
Uranium- and thorium-rich granites and pegmatites are known from a number
of areas in Sweden (Fig, 2). The granites (and pegmatites) occur in a variety
of geological settings in the Swedish Precambrian, and represent a variety of
granite types and ages, 1750-890 Ma (Wilson and Akerblom 1980). Knowledge of
the occurrence and extent of the granites and pegmatities has been obtained
mainly from airborne radiometric surveys and uranium prospecting carried out
principally by the Geological Survey of Sweden (SGU).
For the purpose of documenting the natural radiation environment in
Sweden, and for delimiting risk areas for high soil gas radon contents, the
Geological Survey of Sweden was commissioned to produce a documentation in map
form of all areas and rock types known to be particularly radioactive- The
maps, known as GEO-radiation maps, are produced at the scale of 1:50 000.
They are based primarily upon airborne radiometric surveys, ground measure-
ments of gamma radiation and geological mapping <>
The choice of this method for delimiting risk areas for high soil gas
radon contents was determined by:
210
-------
Granite, normal
Granite U- and Th-
rich
Gneiss
Diorite
Sandstone
Limestone
Shale
Alum Shale
U ppm
2-10
8-40
2-10
0.1- 2
0.5- 5
0.5- 2
1-10
10 -350
Th
5
10
5
1
1
0.
2
2
ppm
-20
-90
-20
-10
-10
1- 2
-15
-10
K
2
4
2
1
1
0.
2
3.
% mRa
-6
-6
-6
_O
-5
1-0.5
-6
5-6
0
0
0
0
0
0
0
3
.1 -
.5 -
.1 -
.01-
.03-
.03-
.06-
0
2
0
0
0
0
0
.1 -21
.6
.5
.6
.1
.3
.1
.6
.5
uR/h
5 -
12 -
5 -
2 -
2 -
0.5-
5 -
20
65
20
10
15
3
18
10 -230
Table 1; Uranium, thorium and potassium contents, radium index and gamma radi-
ation for different rock types in Sweden.
211
-------
Figure 1
1 CALEDONIAN FRONT
2 VASTERGOTLAND
3 NARKE
4 OSTERGOTLAND
5 OLAND
6 SKANE
100km
SGU 1977
212
-------
24°E
65°N
[" "-L AIRBORNE RADIOMETRIC SURVEY
4 J 1969-1979
GRANITES WITH ANOMALOUS
RADIOACTIVITY
AREAS WITH SEVERAL OCCURRENCES OF
ANOMALOUSLY RADIOACTIVE GRANITES
25-60 EXPOSURE RATE (pR/h) MEASURED 1m
ABOVE GROUND LEVEL
SGU 1980
213
-------
1. the assumption that the greatest concentrations of radon in the soil
are directly related to rocks and soils rich in uranium.
2. availability of regional information on gamma radiation from the
airborne and ground radiometric surveys carried out by SGU. These
surveys cover to date approximately 45% of the country.
AIRBORNE RADIOMETRIC SURVEYS
Airborne gamma-ray spectrometry carried out by SGU is used primarily for
regional prospecting for uranium, and as a complementary geophysical method to
geological mapping. The instrumentation has been designed to cope with the
special problems of prospecting in areas of glaciated terraine. Most of the
bedrock in Sweden is covered by glacial till which can vary in thickness from
4 to 10 or more metres. Much of this material is of relatively local deriva-
tion, but it has always been transported to some extent. This latter factor
is of special interest with regard to the radon problem as will be shown later.
The SGU technique (Linden and Akerblom, 1976) is to use four sodium iodide
crystals giving a total volume of 17 litres. Gamma spectra between 0.45 and
2.85 MeV are recorded on 258 channels. The plane flies at an altitude of 30
metres along profiles 200 metres apart, and at a speed of 70 m/sec. Registra-
tion takes place digitally with a measuring time of 400 msec, readings being
taken every 40 metres. After computer processing of the data from all the
channels, the results of the measurements are plotted automatically as maps
using an ink-jet color plotter. Gamma radiation from uranium, thorium and
potassium for each measuring station is marked on the maps as colored lines (U
red, Th blue and K yellow), the lengths of which are proportional to the
registered equivalent contents of these elements (U and Th as ppm and K as
%). The three-component, colored, gamma radiation maps give a detailed
picture of the distribution of the radioactive elements over large areas, as
well as locating point anomalies (Fig. 3a and b).
Follow-up of the anomalous points or areas for each gamma radiation map is
carried out on the ground using handborne scintillometers. Observations as to
terraine, bedrock geology, Quaternary geology and gamma-ray levels are noted
for areas where gamma-spectrometry measurements on the ground have been
carried out. In the compilation of the GEO-radiation maps, all this material
is used together with published geological and Quaternary geological maps
(where available), and detailed local knowledge of the geologists mapping
specific areas.
GEO-RADIATION MAPS
Maps showing radon contents in the ground would be the ideal for environ-
mental purposes. Such maps cannot be produced owing to the enormous costs
involved and the length of time necessary to carry out measurement programs.
An alternative would be to produce maps showing the uranium content (in ppm)
of the ground, but again, this is not yet 'feasible for more than limited areas
in Sweden.
214
-------
I
H-
CW
l-i
ro
OJ
(B
-------
BEDROCK GEOLOGICAL MAP
DOLERITE
COARSE PORPHYRITIC GRANITE
FINE GRAINED GRANITE
| | GRANITE GNEISS
I \\ METABASITE
01234 5km
SGU 1981
Figure
-------
The GEO-radiation maps in their present form are intended as key maps to
show areas where the level of gamma radiation from uranium and/or thorium in
the bedrock or drift cover is particularly high. For this purpose the limit
of 30 pR/h has been arbitrarily selected. To date some 450 maps have been
produced covering approximately 55% of the country. The maps cover initially
areas of alum shale and known uranium-rich granites. The latter category
coincides in general with areas covered by airborne radiometric surveys. The
maps are accompanied by short commentaries on the geology and radioactivity of
the areas concerned. Examples of the maps will now be discussed.
Fig. 4 shows the geological map over part of the alum shale occurrence in
Ostergotland, southeastern Sweden, and Fig. 5 is the GEO-radiation map over
the same area. An enlarged detail from the gamma radiation map over Fornasa
is shown in Fig. 6. The lines on this map are related to gamma radiation from
uranium in the near surface alum shale.
The profile in Fig. 7 shows how Quaternary ice transported fragments of
alum shale from the bedrock exposure up towards the surface of the till in a
southerly direction. The alum shale fragments are successively mixed with
other material during transport.
One can see how individual "nappes" of the shale material develop in the
drift cover, the latter being about 15 metres thick. Comparison between the
bedrock geological map and the gamma radiation map reveals that alum shale
fragments are present in the drift cover several kilometres south of the
bedrock source. In consequence, higher than normal levels of gamma radiation,
and probably enhanced radon emanation, can occur beyond the area of bedrock
exposure of a radioactive rock. Consideration must therefore always be given
to the direction and length of transport of rock fragments when judging the
risks for high soil gas radon contents.
A further illustration of this point is made in Fig. 8 which shows the
gamma radiation map from an area of granite gneiss in central Sweden. The
bedrock is largely concealed by a drift cover of glacial till. A clearly
uranium anomalous area is distinguished south of Svennevad. This area
coincides with a glacial esker and post glacial washed sands. The esker has
its source some 10 kilometres to the north of Svennevad in an area of alum
shale bedrock. The gamma radiation map therefore indicates spread of alum -
shale fragments of the esker and related sands. Enhanced gamma radiation from
uranium concentrations in the granite gneiss bedrock is otherwise only a local
feature in connection with pegmatites and zones of migmatisation.
The gamma radiation, geological and GEO-radiation maps over a uranium- and
thorium-rich granite in Molndal, south of Gothenburg, are shown in Figs. 9, 10
and 11. The suburb of Balltorp is planned to house 15,000 people.
The granite in question is a red to grey alkali granite which partially
weathers to a coarse sand. The granite has a uranium content of 10-30 ppm, a
thorium content of 30-70 ppm and radioactivity of 30-60 uR/h. The granite
is bounded to the east by gneissose granodiorite and to the west by a
porphyritic granite with normal uranium and thorium contents. The whole area
is well exposed and the till cover, where present, is only a half to two
metres thick. The valleys contain sediuents, mainly clay. Glacial transport
of till material was from east to west.
217
-------
^^_, ' i i ^j-^j^^-j ' |-;[ undlffer«ntlatad
PRECAMBRIAN
2O 23 km
10km SGU 1977
Figure
-------
to
H1
GEO-RADIATION MAP
8F LINKOPING NV
LEGEND
GAMMA RADIATION CAN
EXCEED 30 pR/h
GAMMA RADIATION
BELOW 30pR/h
SHALES, LIMESTONES
ALUM SHALE
HIGH CONCENTRATION OF
ALUM SHALE FRAGMENTS
IN TILL
SCALE 1:50000
0 5km
SGU 1980
-------
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|| |l. |«.*...|.*|l|......"|l ,|..l |1||. |....... ||l.|l..|*l|||| l|||||.> -l..|.ll'.|lll"l|.|..'>||lll. l.'lll'.|. 'IIHlll- 1|. I.IIMII.II|.||||....-.'.||.||.t|..|...||. *|l.l*.. . .|..|| ..II.. ......Illll,
-------
N
ICE TRANSPORT
20-40 jiR/h
25MR/h
LIMESTONE
ALUM SHALE
SHALE
SANDSTONE
GRANITE
HI CLAY
{53 TILL WITHOUT ALUM SHALE
HI TILL WITH HIGH CONTENT OF ALUM SHALE
ED TILL WITH LOW CONTENT OF ALUM SHALE
20pR/h GAMMA RADIATION (MICROROENTGEN PER HOUR)
Figure 7
4km
SGU 1979
-------
Figure 8
!1*--S
§ = i :- v
f i =«SVEN&E'VAD
SOTTERN
ESKER
222
-------
GAMMA RADIATION MAP
MOLNOAL
iji
MOLNDAL
1 -Ill
V<- --/• .H||-i4|fJ|»A-M||MmHP--u
-------
NJ
BEDROCK GEOLOGICAL MAP MOLNDAL
01234 5km
LEGEND
Porphyritic granite
Uranium and thorium rich
alkali-granite
Gneissose granodiorite
Amphibolite
SGU
Figure 10
-------
KJ
KJ
un
•t*-» » + + * + + + ** + * + *+ +
*****
*
******
******
******
**-*.***-***.**•***
******
************
*-*
***
**'™v ***«*-»>
r ir 20- »• 36-
«•***•
*********
,
***,«*****
**-*,%*•*,**
GEO - RADIATION MAP
MOLNDAL
LEGEND
GAMMA RADIATION CAN
EXCEED 30pR/h
GAMMA RADIATION BELOW
30}iR/h
ALKALI GRANITE
SCALE 1:50000
1
2km
SGU 1979
Figure II
-------
A program of radon measurements was carried out in the area during the
summer of 1980 (Hesselbom 1981). The results indicate soil gas radon levels
ranging from 30,000 to 500,000 Bq m~3 (relative values).
RECENT RESEARCH
During the last twelve months, a research program has been initiated to
investigate the relationship between radon concentrations in soil gas and
radon/radon daughter levels in dwellings, and to test the validity of the
GEO-radiation maps. Test areas were selected in areas of both uranium-rich
granite (Lysekil) and alum shale (Fjugesta).
Lysekil
In the town of Lysekil, radon daughter concentrations have been measured
in 60 selected houses. Seventy percent of these houses have radon daughter
levels exceeding the permitted limit for new development (70 Bq m~3, Swedish
Building Code, 1981), and 10% have levels exceeding the permitted limit for
existing dwellings (400 Bq m~3).
The town of Lysekil lies on the west coast of Sweden in an area of granite
known as the Bohus granite complex (Fig. 12). The granite occupies an area of
about 20 km by 90 km in Sweden and extends into SE Norway. It has the form of
a large flat-lying, sheet-like intrusion consisting of a series of granite
types ranging in color from red to grey, and in texture from coarse-grained,
sometimes porphyritic to extremely fine-grained (Asklund 1947). Chemically
and mineralogically, however, the granite is fairly homogeneous and the whole
of the granite belt has enhanced uranium and thorium contents (Wilson and
Akerblom 1980). The GEO-radiation maps covering the granite mark the entire
complex as having gamma-ray levels exceeding 30 pR/h. In reality, gamma
radiation from the ground varies between 10 and 50 pR/h, the lower values in
areas where the granite is covered by loose sediments, sands and clays. The
higher values refer to the exposed bedrock. Numerous ground spectrometer
measurements over the granite give the following uranium-, thorium- and
potassium contents: U 9-37 ppm, Th 25-90 ppm and K 3.5-5.0%.
Airborne radiometric surveying has been carried out over the southern part
of the granite. Fig. 13, showing the U-component of the gamma radiation map,
illustrates clearly the intensity of gamma radiation from the granite compared
with that from the adjacent gneisses with normal U and Th contents.
Measurements of radon concentrations in well waters from the Bohus granite
give, in general, high levels. In the Lysekil area, 50% of the investigated
wells (ca 200) have levels exceeding 1000 Bq/1. The levels recorded compare
with those obtained from uranium-rich granites in Maine (Hess et al. 1980).
In the gneisses adjacent to the Bohus granite, radon levels in well water are
low.
Fjugesta
The indoor measurements of radon daughter concentrations carried out in
Fjugesta (45 houses) show that 80% of the houses have levels exceeding the
permitted limit for new development and 12% have levels exceeding the
226
-------
SKAGERRAK
illij BOHUS GRANITE
GNEISS
1Okm
SWEDEN
+ + + + + + t + + + -f+ + + + + + + + +
«• STR0M6TAD+ + + + + + + +
SGU 19S1
SEKIL
227
-------
Figure 13
Illllllllll" I
II I
Illlllllllllllllllll • ..-I' Il-
lllllllll"
minim iiiiii'iiiu
NM|i'i|l|lll'-llll'.ll|i."'illllll
illllllllllliMliiiiiiniiii mi n
lillnili inliiiiiiii
228
-------
permitted limit for existing dwellings. The bedrock of the area, consisting
of flat-lying Cambro-Ordovician sediments including alum shale, is largely
covered by up to 1O metres of glacial till and post glacial sediments. Fig.
14, showing the U-component of the gamma radiation map and the bedrock outcrop
of the alum shale formation, indicates clearly the spread of alum shale
fragments in the till. The geological map over the area is shown in Fig. 15.
CONCLUSIONS
The problem of high soil gas radon levels in Sweden is seen now to be
acute. Rocks and soils with enhanced uranium contents occur fairly extensive-
ly in the country. The normal background gamma radiation in Sweden is 6-1O
yR/h, and vast areas have gamma-ray levels of 12-20 pR/h. Investigations
so far carried out indicate that the GEO-radiation maps, based on gamma-ray
measurements and with an arbitrary limit of 30 yR/h for risk areas,
adequately define the areas with particular risk for high soil gas radon
contents. However, extensive programs of indoor measurements carried out
during the past year by Local Health Authorities and by the National Institute
for Radiation Protection, reveal that levels exceeding the permitted limits
occur sporadically even in areas where gamma-ray levels for the bedrock and
drift cover are considerably lower than 30 uR/h. A number of soil gas radon
measurements carried out by SGU in such an area show that radon concentrations
in the ground can vary enormously from one measuring point to another. A
lower gamma-ray level, for example 20 yR/h, could be adopted for the
GEO-radiation maps, but the consequences of this would be that vast areas of
the country would be placed under stringent building restrictions which are
probably not warranted.
229
-------
Figure 14
GAMMA
RADIATION
230
-------
Figure 15
BEDROCK
GEOLOGICAL
MAP
LIMESTONE
ALUM SHALE
SHALE
SANDSTONE
PRECAMBRIAN BASEMENT
FAULT
0 1 2 3km
I i i i
SGU 1977
231
-------
References
Andersson, A., Dahlman, B. and Gee, D.G. in press. Kerogen and uranium re-
sources in the Cambrian alum shales of the Billingen-Falbyggden areas,
Sweden. Geologiska Foreningens i Stockholm Forhandlingar.
Armands, G. 1972. Geochemical studies of uranium, molybdenum and vanadium in
a Swedish alum shale. Acta Universitatis Stockholmiensis, Stockholm
contributions in geology, XXVII (1), 1-48.
Asklund, B. 1947. "Gatsten och kantsten", Sveriges Geologiska undersokning,
C 479 (in Swedish), 187 pp.
Hess, C.T., Norton, S.A., Brutsaert, W.F., Casparius, R.E., Coombs, E.G. and
Hess, A.L. 1980. Radon-222 in potable water supplies of New England. New
England Water Works Association, 2, 113-128.
Hesselbom, A., Israelsson, S. and Tovedal, H. 1981. Radon in the ground. A
study of methods and instruments for determining radon concentrations in
the ground. Byggforskningsradet, Report R47:1981 (in Swedish), 75 pp.
Linden, A.H. and Akerblom, G.V. 1976. Method of detecting small or indistinct
radioactive sources by airborne gamma-ray spectrometry. In: Geology,
mining and extractive processing of uranium. Ed. M.J. Jones. Institute
of Mining and Metallurgy, London, 113-120.
Radonutredningen, 1979. Preliminary proposals for measures against radiation
hazards in buildings. Report from the Radon Commission, Jordbruks-de-
partementet, Ds Jo 1979:9, (in Swedish) 114 pp.
Statens Planverk, 1980. Svensk Byggnorm (Swedish Building Code). Statens
Planverks forfattningssamling 1980:1 (in Swedish).
Swedjemark, G.A. 1978a. Radon in dwellings in Sweden. Statens Stralskydds-
institut, Report SSI: 1978-013, 1-24.
Swedjemark, G.A. 1979b. Indoor measurements of natural radioactivity in
Sweden. Statens stralskyddsinstitut, Report SSI: 1979-026, 1-11.
Swedjemark, G.A. 1980. Radioactivity in houses built of aerated concrete
based on alum shale. Statens stralskyddsinstitut, Report SSI: 1980-14 1-6.
Swedjemark, G.A., Hakansson, B. and Hagberg, N. 1979. Radiation levels in
houses built on wastes from processing of alum shale. Statens stralskydds-
institut, Report SSI: 1979-006, 1-43, (in Swedish).
Wilson, M.R. and Akerblom, G.V- 1980. Uranium-enriched granites in Sweden.
Sveriges geologiska undersokning, Rapporter och meddelanden, nr. 19,
1-30.
232
-------
FIGURE CAPTIONS
Fig. 1. Distribution of the alum shale formation.
Fig. 2. Distribution of known radioactive granites.
Fig. 3a. Uranium-component gamma radiation map over a uranium- and thorium-
rich granite near Vasteras, central Sweden. Original scale 1:50,000.
Fig. 3b. Geological map over the same granite. Original scale 1:50,000.
Fig. 4. Geological map for the. map sheet Linkoping NW, southeastern Sweden.
Original scale 1:50,000.
Fig. 5. GEO-radiation map for the map sheet Linkoping NW, southeastern
Sweden. Original scale 1:50,000.
Fig. 6. Uranium-component gamma radiation map over Fornasa, Ostergotland.
Original scale 1:50,000.
Fig. 7. Profile illustrating the distribution of alum shale fragments in the
Quaternary drift cover.
Fig. 8. Uranium-component gamma radiation map over Svennevad, southeastern
Sweden. Original scale 1:50,000.
Fig. 9. Uranium-component gamma radiation map over Molndal, Gothenburg.
Original scale 1:50,000.
Fig. 10. Geological map over Molndal, Gothenburg. Original scale 1:50,000.
Fig. 11. GEO-radiation map over Molndal, Gothenburg. Original scale 1:50,000.
Fig. 12. Geological map over the Bohus granite complex, western Sweden.
Fig. 13. Uranium-component gamma radiation map over the Bohus granite around
Lysekil. Original scale 1:50,000.
Fig. 14. Uranium-component gamma radiation map over Fjugesta, central Sweden.
Original scale 1:50,000.
Fig. 15. Geological map over Fjugetsa. Original scale 1:50,000.
233
-------
AN APPARATUS FOR CALIBRATING PASSIVE
INTEGRATING RADON MONITORS (PRIMs)
Robert A. Washington
Atomic Energy Control Board
Post Office Box 1046
Ottawa, Canada
ABSTRACT
A description is given of a chamber used at the Atomic Energy Control
Board laboratory for the calibration of passive radon integrating monitors
(PRIMs). It has been proven capable of providing stable and reproducible (to
_+ 5% or better) concentrations of Rn^22 in air frOm about 20 pCi/1 (740
Bq/m3) to more than 3,000 pCi/1 (111,000 Bq/m3). The temperature range
employed was 25° to 30°, and the relative humidity was in the range from
58% to 62%. The results indicate that a calibration curve of the form y = mx
+ b (where y = cumulative radon exposure in picocurie-hours/litre, and x is
the TLD reading in nanocoulombs) provides better information about PRIM
performance than a simple calibration factor k = Y/x.
234
-------
OPEN DISCUSSION I: AUGUST 27, 1981
Open Discussion; Instrumentation and Measurement Methods
Moderator; Peter G. Groer
Panel; Speakers for Sessions I and II
Ron Colie
Andreas Wicke
James E. Gingrich
Howard H. Prichard
Andreas George
Donald J. Keefe
Susan Hinkins
Lyle H. Rathbun
John G. Pacer
235
-------
PROCEEDINGS
MR. PHILLIPS: I know it's not convenient to go to a microphone every time
you have a question, and in a discussion session like this it will be even
more difficult. But I think it's important to try to get this portion of the
program in the proceedings. We're not only taping these sessions, but we also
have a recorder—not a mechanical recorder obviously—with us for that purpose.
So it's important, again, that you identify yourself into the microphone.
And, for the microphone on my left, again, be sure to speak directly into it.
I made one mistake, one bad mistake, this morning. The paper by Melvin
First listed in the proceedings i^s to be presented by Stephen Rudnick, and it
will be presented. I apologize for that confusion.
The moderator for this session is Peter Groer, who you know by now, if you
didn't know him beforehand. So, Peter, I'll turn it over to you.
MR. GROER: Well, thanks. For the first few minutes, I'd like to see how
things are going. So I'll open the session to the floor, and I think we'll
just accept questions.
Please identify yourself clearly. When you use technical terms, try to
pronounce them as clearly as possible. It's quite a job to record all of
these accurately. I have experience from other meetings; it's very hard to do.
We'll start just with an open question session and we'll see which way the
discussion turns.
MR. HOLUB: Question to you. You mentioned the statistics. I remember
that Lucas said that if you count the same nucleus twice, once as radium A and
once as radium C prime, you have greater error than just Poisson statistics,
square root of the count, indicate. Do you have any feeling of how much that
is?
MR. GROER: You are correct in pointing to Henry Lucas. He has done very
interesting work in this area—together with an applied mathematician at
Argonne. The results he has are not applicable to radon daughter counting. I
have looked at the problem, and, as I said in my talk, I cannot calculate the
variance for the daughter and the granddaughter. For radium A it's very easy.
Okay. So, you're invited to try to solve this. I don't know the answer.
MR. HOLUB: In which sense did Lucas make a mistake? Why was he wrong?
MR. GROER: I did not say that he made a mistake. He looked at a
different problem. He was not concerned with radon daughter counting. It's
the paper—I hope we're talking about the same paper—it's the paper in the
Journal of Applied Physics, I think.
MR. HOLUB: Yes.
MR. GROER: He is not concerned with the problem of radon daughter
counting.
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MR. SCOTT: I was just struck by the fact that literally everyone seems to
be concerned with radon daughter counting, with the possible exception of the
Germans. What about thoron? I mean, how come we're discriminating against
thoron so effectively? Is thoron a problem or do we just ignore it?
MR. GROER: I think that's a very good question. If there's anybody here
on the panel who would like to answer this, be my guest. All I can say is
that I made many measurements in the U.S. in uranium mines and in other
locales—then spectroscopically—and I've never seen thoron daughters. But I
know that it's a problem in Canada. And I am sure there are people here who
know what the thoron daughter concentrations are in Canada. David, to this
point?
MR. ROSENBAUM: I think the basic policy reason and the reason in the ORP
why we haven't done anything on thoron is that the health effects data are all
in terms of radon daughters. And, therefore, if you want to know the effect
on somebody you look at the radon daughter concentrations, the working levels,
and from that you induce the danger, the risk.
Now, the implicit assumption here is—and that's because the original
measurements in the mines threw away the thoron—that either thoron is so
small that it isn't a problem, and therefore doesn't make any difference, or
the ratio of thoron daughters to radon daughters is the same as it was in the
mines. And, therefore, when you throw it away the health effect still comes
out right. Undoubtedly, there are situations in which both those assumptions
are completely wrong.
MR. SCOTT: If I could just carry on with this. One place where it does
strike me as being particularly important (I may point out, I am from Canada
and there isn't all that much thoron around, but it is present.) is in the
kind of instrument that does estimates of radon daughters by, say, alpha decay
or possibly even alpha spectroscopy plus beta counting. The resulting
estimates will be severely distorted with even the presence of a small amount
of thoron, particularly in the beta plus alpha ones.
MR. GROER: No doubt about it, if you have thoron daughter concentrations
that are high enough, they will, since they fall into the two different alpha
channels, the upper alpha channel, there is no doubt about it that this will
distort measurements. So the instrument you heard about today cannot be used
in its present form in atmospheres where there are thoron daughters. I agree
with you.
MR. PERDUE: If I might make a comment on the thoron. Of course, there is
another radon we haven't talked about, which is 219. But anyway, I think
we'll all agree that in the world in general, thorium, in background levels,
is larger than the amount of radium there is in the soil, quantitatively, or
by weight. So if one takes measurements approaching background levels, there
has to be thoron in it. And you can measure this.
MR. GROER: Well, there's one big difference in the two decay chains.
That's the half life of the noble gas, right? And that makes a difference.
So it depends very much on your situation. I don't dispute the existence of
it, but radon-220 does have a short half-life.
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MR. PERDUE: That is easily explained. Radon-222 may decay in the next
state, but radon-220 decays right where you are.
MR. ROESSLER: Just one small comment on the thoron question. In the
heavy mineral industry, in particular I'm looking at zircon mill and products,
using two total alpha counts at different times—I guess, a rock—we did find
both radon daughters and thoron daughters. In fact, if you calculate in terms
of working levels, the thoron daughter working level of that particular case
is slightly higher than the radon daughter working level. But the summation
of the two is still several orders of magnitude below occupational standards,
so we never really followed through on that in any great detail. But there
are places where we're going to find thoron daughters, yes.
MR. GROER: Okay. Any more comments on the thoron and thoron daughter
question?
MR. ROSENBAUM: The National Radiation Protection Board estimates that
there is about ten percent as much thoron as radon in a typical house. I
don't know if that is peculiar to Britain or the building materials that are
used or what it's from, but that's the kind of numbers that they use. And
they might be enough. I'm no kind of instrumentalist, but that might be
enough to interfere with some of the measuring techniques.
MR. COHEN: One last comment on thoron. My lab is in the United States,
and there's plenty of thoron in it. In fact, it puts a fair correction on the
radium A peak, enough to really make a difference in our lab at least.
MR. GROER: What causes the correction to your radium A peak? Thoron?
MR. COHEN: There's a thoron alpha that is the same energy as the radium A.
MR. GROER: Yes, but why do you think that you have thoron in your filter,
if you use a filter method?
MR. COHEN: Because there's also a thoron peak at 8 point—8 MEV. But
there's also a thoron daughter at 6 MEV.
MR. GROER: I agree, but not that it's thoron. I mean, it was technical.
It's just a little difference. You said thoron and 1 said no, but that it's a
thoron daughter I agree with you. In the houses where we have used this
instrument and in the uranium mines with the channel analyzer underground, we
have never seen a thoron daughter peak at higher energies than, well, above
7.68 MEV. What is the alpha energy? I think it is 8.7 or something like
that. Our highest flow rate, as I mentioned to you, was 40 liters per minute.
But we are sampling only for two minutes.
So, if there are no more questions on the thoron daughter, I'd like to
steer the discussion a little bit. I want to bring up the question of
availability of commercial instruments—how satisfied people are. I was asked,
you know, to bring this up. How happy are investigators with commercial
instrumentation? What are the problems? What instruments should be produced
commercially? Is there a need for a certain type of instrument? Is there any
interest in this topic?
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MR. HOLUB: I'd like to mention the problem of acquiring a constant radon
source one can rely on for these calibrations. And we have some commercially
available dry sources too—EPA brought some. We have had bad experiences;
some people have had better experiences. Now the onus is really on NBS to
produce something really good. The idea is to provide a known, reproducible
radon concentration at any time. So, I wonder how interested others are. We
certainly are. I think it would be useful to have them.
MR. GROER: If I understand you correctly, you're calling for a radon
meter that would measure—
MR. HOLUB: Radon source. Always produce a given amount, hopefully a
solid source, so that you don't spill it. The more I question, the more I
think NBS is going to do it.
MR. COLLE": Well, yes—
UNIDENTIFIED SPEAKER: Stop right there. Good concise answer.
MR. COLLE: The onus may indeed be on us. What he was referring to, of
course, is some type of solid source to replace our solution standards.
Although there are laboratories that can use solution standards—use them very
well, perhaps better than we can—there is a real need out there for a solid
source, something like the commercially available source, which would be very
easy to use. We have a very limited effort underway looking for a replacement
in a solid source. And, if the onus is on us, the last comment I'd like to
make is, if you see me, I'll tell you who to make the check out to.
MR. KAHN: What about a liquid source with two valves on it so you can
bubble? What we need is some source that can be used over and over again. Is
there any problem with that?
MR. COLLE: Well, we had a small meeting, with a few people, some EPA
people, and for such a type of source, we discussed several types of
configurations. One of them was a solid source like ion exchange resin
impregnated with radium, in which case somehow magically either the radon
would get out of this material into a solution and then you would take it out
of the solution, or perhaps take an aliquot of that solution for making radon
in water analyses.
We have considered about three or four different designs, none of which
have been excluded yet, and your type of proposal is being considered. I must
say that this effort is relatively low key, but they are being looked at.
There are several possibilities and that which you've mentioned hasn't been
excluded.
MR. PHILLIPS: Since I suggested, Peter, the question about the commercial
instruments, I feel compelled now to try to continue comment on that. I have
not used the newer commercial radon daughter instruments, but I have looked at
a few of them and, just from initial observations, it appears to me that there
may be some problems in the intake portion in terms of plate out, prior to
deposition of the daughters on the filter. I know in particular you were
concerned about this for the instrument that you and Don worked on. I wonder
if there is any other comment on that, particularly from you.
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MR. GROER: As you probably remember from the figures you saw on the
slides this morning, we tried to keep the air inlet completely unobstructed
because we were worried about the so-called umbrella effect, that we are
losing the aerosol particles on possibly the detector that shields the air.
Now, I do know that there are commercial units around that measure radon
daughter concentration, or I should say total alpha counts, rather than
individual radon daughter concentrations. Very little care has been taken to
avoid plate out problems. I have seen an instrument where the air inlet is
quite a small opening, and then a few inches away from that is the filter.
There is just no doubt in my mind that you will lose some of the radon
daughters on the way to the filter.
So, I think this is an important problem, and I think manufacturers should
be made aware of that. Unfortunately, as long as there are customers who buy
these units, the manufacturers will not be forced to change their assembly
lines.
MR. KEEFE: I'd like to make one comment with regard to the problem of
plating out on the detector. From an engineering standpoint, one of the
problems that you have is that it's easy to design an unobstructed air intake
port. The basic problem is to get the filter membrane from point A to point
B, and this is the area that costs a lot of money. This is also where your
mechanical problems lie, I'd say 30 percent of the cost of our instrument
lies in that particular problem. Industry is going to have the same problem,
except they're looking for a product that is lower in price, that has a good
market and saleability, and they're trying to cut in that area, I feel.
But, if the scientific community and the people who are interested can
bring out the point that plate, out is a serious problem and they should
consider these things even though the costs of their instrumentation may go
up, I think they may make some changes in their instrumentation and they could
solve that problem.
MR. NYBERG: We have looked at—in our lab—quite a few instruments, not
as many as Andy George, but then I don't think anyone has. I think as an
electronics engineer I can say, speaking, I think, for some of us, that the
instruments are getting better. Just in the last few years we have seen an
awful lot of newer, better, smaller, lighter, more versatile instruments
coming out. One of the problems that we have that maybe could be addressed by
this group is how do we evaluate them? Now we send them to Andy or some such
thing. This business about plate out on the detectors is a very common
problem. There's a much too tortuous path for these daughter instruments.
But there is not even a semi-standard way of evaluating this at the present
time. I'd like to see if someone has some suggestions for looking at these
things in a little more organized fashion than we're doing right now.
MR. GROER: Thank you. I think that's a very good point. It also leads
to the question of intercalibration and things like that. I'm sure that some
of our panelists here will have some ideas on that.
MR. COLLE: No, I don't have ideas on it. I just want to reinforce the
point and perhaps give you something else to think about. What we have in
this room is a collection of probably the premier laboratories in this area.
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What you have to keep in mind as well is that most of the radiation protection
being done in this country is being done by state laboratories, and the fact
of the matter is that their instrumentation needs are considerably different
than research laboratories' needs. They need instruments that are very
reliable and relatively inexpensive, particularly if they have many sites to
cover. They cannot spend 10 or 20 thousand dollars for an instrument.
Another matter related to calibration and the reliability of instruments
is that there really should be some type of evaluation of instruments to guide
some of these other laboratories. These laboratories are not equipped to do
the type of evaluations that your laboratory may be able to do, and it would
be a great service to them to have this evaluation. Also, there is a great
need, once an instrument and/or method is evaluated, to assure that it's
compatible, on a continuing basis, with other things.
These are just additional thoughts that I think we should keep in mind.
We shouldn't overlook that there is a bigger user community out there than
just the people in this room. Now, I will leave the floor open for the ways
to do that.
MR. KEEFE: Speaking of calibration, again, and the problems, and state
agencies. I have received calls from several state agencies with regard to
calibration of the EWLM, which belongs to the EPA, which they have loaned out
to some state agencies. They are presently involved in one specifib case in
the state of Montana in lawsuits versus various cities and mining companies
and so forth. Immediately they get involved in having to prove the
calibration. The measurements that are made with this instrument must be
documented and proved. Again, you're back into the calibration problem.
One of the problems I'd like to mention about calibration, and it was
mentioned before, is that people have been using these radon chambers, I hope
basically for calibration of radon instruments, not necessarily radon daughter
instruments. One of the problems that you have in these large bags is that
the volume of gas that's contained inside the bag is not sufficient for our
calibration. What we have to do in all our calibrations is go to the uranium
mines. We have to go to the Bureau of Mines research mines and use that large
volume of air and try to keep the air as static as possible to make our
calibration.
Certainly the scientific community could use some sort of a calibration
laboratory where it wouldn't have to go that far. Try that in February
sometime—in the snow. It's an interesting experience.
MR. GROER: February in Colorado is okay if you ski down. With this,
maybe we can leave this topic, or is there further comment? I don't think we
really have solved anything. What I personally don't see is how we could get
a national quality standard for instrumentation like that. Okay, why not?
Let's hear your ideas.
UNIDENTIFIED SPEAKER: I don't have anything more to say. I just wondered
why not.
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MR. GROER: I just wanted to hear some suggestions. I mean, who would you
suggest to be the supervisory agency? The National Bureau of Standards? Some
other agency?
MR. PERDUE: I'd just like to say that we've been here most of the week
making intercomparison studies of existing instrumentation, and I feel that
unless a lot more of these studies are made we're never going to really solve
what's going on. There's a number of problems that haven't even been
approached. What happens with humidity? Does this change the radon daughter
attachment? What happens to the other isotopes? We know sometimes they are
indeed present. So, unless we can address first the things we know, we can
get Bureau of Standards radium that can be calibrated and, of course, can go
back to what they've got. Can we really know what's going on unless we keep
this thing up? We are, each one of us, working in a little pocket and we're
getting data and we don't know whether it matches somebody else's data or not.
MR. COLLE: I think the important point is that it's very admirable that
these things keep up. But the problem is this. You have an informal group of
six or seven laboratories—and perhaps these six or seven laboratories can
answer some of these questions for the other laboratories—but what do the
other 30 or 40 laboratories who are also making these measurements do?
MR. RATHBUN: It occurs to me that a lot of the other work like this
that's being done has been farmed out to independent companies. And it seems
like at this point there is no national agency that wants to be the arbiter
for such a project. Why not have an independent group bid on a contract to do
this type of work and let each person that wants something calibrated pay a
certain fee to bring it in?
MS. FISENNE: I'll help you out on that one.
MR. GROER: We should have comments on this one.
MS. FISENNE: All I can say to that is that's why we have the National
Bureau of Standards. So, if somebody is willing to come up with contract
money, they will obviously address this problem. I don't think it has to be
done as a private industry project. Obviously, the National Bureau of
Standards is exactly that, at least in this country. They provide us with our
radium standards right now. So if everybody is that much interested, then we
should be able to get the money together to allow them to remain again on
national standards in this area as well.
MR. COLLE: Thank you. That's indeed the point. We have had this type of
initiative literally proposed for perhaps a little longer, but definitely for
three years. It has ranged from a couple of hundred thousand dollars to
multimillion dollar efforts proposed from every possible point of view that
you could perhaps think of. You know, we've tried to beat the bushes in all
sorts of ways. We thought we hit all the right things and everything else.
We have not been successful yet.
We recognize there is a need out there for basic national standards for
these measurements. We would like to make an effort to try to provide this.
There are probably other laboratories which right at the moment could do a
better job of it, but by congressional fiat we have the national
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responsibility to maintain these things. We have both the long-term interests
and commitment to maintaining these things. And I can't agree more with Sue
that it should be done on a national basis. That's why we were established as
this type of laboratory. And it just takes more of a push than we've been
able to provide ourselves.
MR. GROER: Great. What could be the first step?
MR. HOLUB: To make a list of problems and agree on that.
MR. GROER: Can you be a little more specific?
MR. HOLUB: For instance, as I said before, the plate out, the charge, the
trace gases, and the humidity—these I consider a beginning—and then the
techniques of spectroscopy versus total alpha and error propagation, perhaps
in more detail. What happens if the concentration changed during the sampling
and it's simply error propagation?
MR. GROER: I agree with you. It is an important research problem. But I
think we just addressed slightly different questions. The question was about
intercalibration, standardization, possibly of instruments. My concern is how
do we take the first step as a group if the National Bureau of Standards is
the agency that would be entrusted with such a venture?
MR. COLLE: I'm not sure. I'm not sure of the mechanism. I just know
that it requires money and personnel, both of which we are drastically short
of. How the money comes is not our most important concern. We would
certainly not turn down a multimillion dollar contract or interagency
agreement. We would prefer direct funding to our own appropriations since
that's more stable and one can build continuity in programs. But we have some
plans. We have had these plans for a number of years, and it's just a
question of putting them into our program and funding them. The mechanism to
do that is to have Dr. Rosenbaum write us out a check.
MR. GROER: Well, that was certainly a clear answer. I think Bob Holub
addressed some interesting questions this morning, and he just reiterated some
of them. I'd like maybe to take up the first one. What do we know about
radon daughters immediately after? By immediately after I mean, maybe a
picosecond or maybe a nanosecond after they were formed in vacuum. What do we
know about that? What charges are there on these, and then what happens from
there on? Would anybody like to tackle this question?
Well, there are papers in the literature that tell you exactly what the
charge states are for a radium A or for a thorium A. But this is all measured
in vacuum—not the typical condition. And then, of course, the neutralization
of these daughter products after they are formed is an area that's very poorly
understood.
I think there's a research project going on at the University of
Illinois. Does anybody knows about this project? Is there somebody here that
works in this area? Bob?
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MR. HOLUB: That's the project that was funded by the Bureau of Mines, and
it has been stopped, not for lack of funds. But the basic facts are that
usually people assume that 90 percent of all daughters in the air are
positively charged. Now, in 1914, as I mentioned before, Welish found-that
the few have ether, lots of ether; he obviously didn't have a hundred percent,
but lots of ether in the atmosphere, (and) none of the daughters was charged,
none. In the arrangement similar to what Andreas Wicke has shown there simply
was no correction due to charge.
MR. GROER: Excuse me. Can I interrupt you? This reference will have to
go into the record. Could you possibly share it with the group? I think it's
an interesting reference, which I personally didn't know.
MR. HOLUB: Yes. Most people reference it, but no one reads it.
Unfortunately, I don't remember the full reference, but I can give it to you
tomorrow.
In the experiment done in Illinois, published in January in Science, they
did exactly what Jess Thomas did, except instead of air passing through they
had nitrogen with various trace gases. And when they had 10-ppm and N02,
the diffusion coefficient was such that it must have been neutral. It was, by
the way, about twice as fast as when it was charged like impure nitrogen.
It's a very simple and easily understood experiment.
The Canadians did a similar experiment (published in Physics in March) ,
and they had pure gases. When their ionization potential was lower than
argon's their results basically confirmed what Hopky found at the University
of Illinois. Instead of trace gases, they simply used other gases, like
acetylene and formaldehydes and C02 or something—I forgot, there are quite
a few gases. They all have lower ionization potential than argon; however,
they still have higher ionization potentials than polonium.
In Bombay there is an Indian group, Cotropi. They looked at ether.
Apparently, besides the ionization potential, the ion molecule reaction also
plays a role. All these ion molecule reactions are taking place within a
period of microseconds. And, by the way, some people use the term "born
neutral," even though, of course, it's not very likely that the daughter is
neutral and is slowed down.
So, that is a very difficult problem. And it depends on trace gases.
Now, the number of hits per molecule per second is ten to the ninth, so it's
basically, if you are ten to the minus ninth of something in the air, still
it's going to be a hit once a second. So you can imagine the terrible problem
this might be. Even though, as you all say, for practical purposes maybe it's
not necessary, but it should be looked into. That's the review of what
happened in this in the last half a year or year.
MR. GROER: Okay. So, if I interpret the situation correctly, there is no
systematic research effort in this area—neutralization of, let's say, newly
formed radon daughter products in the atmosphere, whatever this means.
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MR. HOLUB: That's it exactly. We are trying to do something, but it is
very difficult.
MR. GROER: Is David Rosenbaum here? No? Well, this is certainly, I
think, an interesting question. Humidity was brought up. Now, there are
many, many different questions related to humidity. Calibration, filters,
TLD, track etch, plate out, I don't really know where to start. If anybody
here, the panelists, the audience, has a particular humidity problem he would
like to bring up, please do so.
MR. COHEN: This question is related to what you just said. If I
understood Jim Gingrich this morning, he said that what a track etch detector
measures is what is plated out on it. Now, if that's true, then it must be
sensitive to what the plate out conditions are. And, if plate out conditions
are sensitive to humidity and all these other things, how can they just be a
measure of radon, the radon daughters?
MR. GROER: Jim?
MR. GINGRICH: The current type of detector we have now will measure
whatever is plated out on the surface. But for precise radon measurement,
Bernie, we use that type F cup. All right, what it does is filter out any
radon daughters that are outside the cup. So the only thing that gets through
the filter is radon itself. Radon itself will then go into the cup, plate out
on the walls and sides of the cup, and plate out on the detector's surface
itself. You'll get some signal from the radon that's still in the cup and
some signal from the plated out materials on the side of the cup. Does that
answer your question?
MR. COHEN: It's a clear answer, except it doesn't agree with things I've
heard. I've heard that, for example, if you put a solid state detector where
the detector is, you get a clean spectrum. It's as though everything that is
being detected is the stuff that is actually plated out on the surface. And
if that's true, then even in the cup you're measuring stuff which plates out
on the surface of the detector. Am I wrong somewhere?
MR. GINGRICH: Oh, yes, you are measuring stuff that plates out on the
surface of the detector in the cup, but you've got to remember that the only
thing that will get through the filter is radon. So the signal that the
detector sees is directly proportional to the total amount of radon that has
come through the filter.
MR. COHEN: The radon comes through the filter and is in the cup. All
right?
MR. GINGRICH: Okay.
MR. COHEN: Then it decays into daughters and, as I understand it,
essentially what happens then is only the radon daughters which plate out on
the detector are detected.
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MR. GINGRICH: No, that's not correct. It is seeing those radon daughters
as well as the alpha particles from other radon daughters that would have been
plated out on the walls of the cup—and also a signal that is directly from
the radon itself because the detector does see a certain volume of radon gas.
MR. COHEN: But what's the support for this? I mean, is it true that if
you put a solid state detector there you get a clean spectrum with only
peaks? That's what I've heard.
MR. GINGRICH: I'm not an expert on solid state detectors.
MR. COHEN: Well, how about with your tracks? I mean, are all your tracks
the same? Do they have only two different lengths?
MR. GINGRICH: No. You'll see a full spectrum of tracks. And the reason
you will is because if you look at the volume, first, the important thing is
where do the alpha particles start within the volume? All right. If it
starts some distance out, then by the time it gets to the detector the track
that you see in the detector will be fairly small compared to a track that
would have started from an alpha particle fairly near.
MR. COHEN: That's what I was asking. You actually have data looking at
the length of tracks, and you found that the tracks do have all different
lengths?
MR. GINGRICH: Oh, yes. It's a full spectrum.
MR. PHILLIPS: What you said is true; at least I have done that. If you
put a solid state detector i-n those cups, then what you see is a clean A and C
prime spectrum. But I think you have to consider the conditions and the solid
state detector construction; it has a bias on it, too. So that may not be
directly relatable to the track etch situation.
MR. HOLUB: We have done this, too, and the detector on the surface is
neutral. The bias probably would not play a role if the daughters were not
charged. But there is no bias on the surface of the detector.
MR. PHILLIPS: That's true, if it's operated at a positive potential with
a negative potential or ground on the outer surface of the detector.
MR. KAHN: Well, what does that say about the radon? You also see the
radon alphas.
MR. PHILLIPS: No, I didn't. In the counts that I did, and these were
integrated counts over fairly long periods of time—about an hour at
concentrations, let's say, of 50 picocuries per liter, equilibrium around 25
percent—I saw essentially no radon in the spectrum.
MR. KAHN: Can you explain that?
MR. PHILLIPS: My explanation—
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MR. GINGRICH: Well, I would agree with you. There's actually a paper
that's published on this, and I could give you a reference to it. It's by Dr.
Bob Fleisher and tells the contribution of radon and radon daughters, the
alpha particles, where they plate out, and so forth. But, as I remember,
something like 30 percent of our signal in the cups, in the normal geometry,
is due to radon, and the other 65 percent is due to plate out on the side and
on the detector. I can check those numbers for you, but I can certainly give
you a reference to it.
MR. KAHN: But that doesn't seem consistent with his observation.
MR. GINGRICH: I don't know how to explain that inconsistency, I'm sorry.
MR. PHILLIPS: There's another interesting situation that I haven't been
able to explain. (I might add that all of this is preliminary work; I have
not followed up on it because I got busy with other things.) If you put it in
a filtered cup, you see a clean spectrum, and the heights of the A and C prime
peaks are about the same. If you remove the filter at the same concentration,
the C prime peak is roughly twice the height, or as many counts, as the A.
Somebody tell me why.
MR. GROER: Bob?
MR. HOLUB: In answer to the first question, it depends simply on how big
the cup is. If you see the radium A and C prime from the walls, then, of
course, you get contributions; it's not a clean spectrum. But, you remember,
for instance, in the case of Dr. Vickers' experiment, he had a clean spectrum,
too. But, of course, he had a charge there. And then the answer to your
other question is a matter of equilibrium. If you don't put the filter there,
then you have a different case than if it's coming from the outside.
MR. PHILLIPS: Right. But why would you expect to see twice the amount of
C prime as you did A, irrespective of the equilibrium? I can't explain that.
MR. GEORGE: You said you have no filter in the cup?
MR. PHILLIPS: Correct.
MR. GEORGE: So you're getting the radium C prime from the decay of radium
A that's in the clean cup, and if you remove the filter you get an additional
radium C that's in the air.
UNIDENTIFIED SPEAKER: But you always have more A than you have C prime in
the air.
MR. GEORGE: I don't know much about spectrometers, but I think that's
probably one of the reasons.
UNIDENTIFIED SPEAKER: How do you get more C prime than A in the air?
MR. PHILLIPS: I would believe, though, that if you had the filter on the
cup and you left it for a sufficient time, wouldn't you expect a hundred
percent equilibrium in the cup? That's what I would expect.
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MR. GEORGE: I don't know.
MR. PHILLIPS: So I would think that the highest count would be when the
filter was on the cup. I think that you'd have an equilibrium situation.
MR. GINGRICH: Excuse me, Chick. But I'm pretty sure you wouldn't expect
a hundred percent equilibrium in that cup. The reason for it is that you've
got a lot of plate out surfaces.
MR. PHILLIPS: Yes, but what I'm looking at is all the plate out. Because
I'm seeing a clean spectrum. I'm seeing nothing from the walls. Or,
essentially nothing.
MR. GROER: Bob?
MR. HOLUB: One more. We can discuss this later in detail, but in
experiments done by Eugene Benson at the University of San Francisco they had
a cup, a collimator, and it was supposed to measure radon daughters in the air
together with radon by means of collimating in such a way that from one volume
you would get only radium A and from the other radium C prime and radon. In
other words, a perfect system. However, the collimator—it's really a sink
for radon daughters for plate out—is just a few centimeters long in diameter,
quite small. And still the daughters practically never made it, the alpha
particles from those appropriate volumes never made it to the surface, to the
track etch. If you look at the depletion of concentration of the-daughters
close to the wall, it simply is that there are no radon daughters. It happens
very quickly and it must be very complicated inside the cup. You simply can
have practically no daughters there. It can go anywhere almost. I'm not
surprised that you see all kinds of things.
MR. PHILLIPS: Well, I would agree wigh you, except the only plate out I'm
looking at is that which is on the detector. I'm not seeing the plate out
from the walls.
MR. HOLUB: That's right. You are not taking care of the whole thing.
Maybe it's escaping here and there. Almost anything can happen.
MR. PHILLIPS: Well, you might be right, but I don't know why taking the
filter off of the cup makes it behave that strangely.
MR. HOLUB: These cups, when you touch them they're very easily affected—
four thousand volts, and then inside it's plus and outside it's minus and
there are spots that are even higher. So it can happen just by touching it.
MR. PHILLIPS: Yes, but it's the same every time, and I don't think I
touched it.
MR. HOLUB: No, no. You have ten cups altogether and you take the one
apart from the other and they are all completely different.
MR. PHILLIPS: I realize that. But every time I performed the experiment
I just described, the same thing happened.
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UNIDENTIFIED SPEAKER: Got the same results regardless of the variance.
MR. HOLUB: Then I don't know.
(Laughter.)
MR. GROER: The record should show that. I think without a blackboard,
it's sort of hard to follow. I've sort of lost track visually at some point
in this discussion. It's a very interesting question, but I don't think we
can settle it. At least, my visual imagination is not good enough. Maybe
with a pad of papers it can be settled at dinner this evening, I don't know.
Time passes quickly. I've asked in the initial phase for input from the
audience. I would now turn the discussion around so the speakers can ask our
panelists to make comments, suggestions, raise questions. I will start on the
right end of the table here. Ron?
MR. COLLE: I think I've said enough. I have nothing else.
MR. GROER: Okay.
MR. WICKE: I want to ask Jim about his experience with charging his cups,
if he did some experiments on this. It seems to me an important factor
because when you make calibrations you assume that the distribution of the
daughters which are plated out in these cups is reproducible. I think it
might be due to charges that it is not reproducible, and that will produce
some errors.
MR. GINGRICH: I think the whole question of charge on the cups has been
overplayed a little bit and I say that because of our experience of making a
lot of measurements, not that we've made a lot of precise charge measurements,
but a lot of radon measurements. We've calibrated these detectors in
something like six or seven different chambers over various periods of time
under quite different conditions and so forth, and yet the data all fall
pretty good on that calibration curve line. If there were charges that are
maintained on the cups for long periods of time, and other considerations like
that, I'm sure that we would see a much bigger scatter in our data. And we
just do not see that scatter. So that's one empirical reason we think that
the charge thing is maybe overplayed a little bit.
MR. PRICHARD: I'd like to direct some questions to anyone who may have
been doing some work with activated carbon or other sorbents in concentrating
or making integrated radon measurements. In particular, I'm interested in
relative humidity and volume dependences. Any comments? Andy?
MR. GEORGE: Now, as I said earlier this morning, we just really began to
look into this M-ll activator charcoal canister, and we haven't done too much
in terms of humidity effects and temperature. Although I looked at the
temperature range that you find normally in the indoor environment—and I
assume for this kind of application for getting data like screen data, I
thought that was sufficient. As I said, this area needs to be investigated.
So I don't want to say this technique is ideal until you check it further.
I'm only suggesting that it may be a convenient technique, and it's very easy
to test this technique.
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Now Jess Thomas back many years ago did some of these experiments, and I
know there is some application, and I thought I sent you a copy. See, I don't
forget. I sent you a copy, and I thought maybe you found the information that
you needed. If you are not happy, I guess you have to contact Jess Thomas,
because he spent a lot of time on that.
MR. PRICHARD: I was referring less to the cases in which you actually
pull air through the canister. Where you just use the canister, rather, a
volume of charcoal as a passive absorber, such as the previously mentioned
unit and the M-ll.
MR. PACER: We did some time tests using charcoal as a flow-through device.
At room temperature and humidity, which in Grand Junction is probably about
10, 15 percent (we just wanted to get some initial numbers) one M-ll had
absorbed something like 90 percent of the radon that it was exposed to within
the first five minutes, and then it absorbed up to 97 percent after the first
hour. The other units were a lot slower. It took about 20 minutes to absorb
the first 85, 90 percent, and it took on the order of four hours to get to 97,
98 percent. So, there is a time dependency on that absorption, and I think it
has to do with the difference in the volumes of the charcoal.
MS. HINKINS: I just have a couple of comments. Since I'm a statistician,
my comments are mostly based on the data. This is probably not a discussion
topic and maybe it's something you all do already, but it seems important to
document your data in the sense that if you want to go back and look at the
calibration results you can find not just the amount of time that the devices
were in the chamber, but the actual dates they were in the chamber—not just
the total exposure, but the radon concentration and the exposure time. And as
much data as you can think of to put in. That's very helpful when it comes
down to analyzing the data.
And one other comment on calibration. I find the method of displaying the
calibration data a little confusing. From my background I look at it as an
independent variable and a dependent variable and you're trying to fit a
slope. And, for a Poisson distribution, a better estimate than the sum of the
ratios is to take the ratio of the sums. Those are the only comments I have.
MR. PACER: I just have two comments. One is, I agree that we need some
radon standards and I think we'd support NBS doing that. The other thing is,
one of the things I was interested in coming to the meeting for was to learn
something about radon flux measurements and their calibration, especially
since EPA does have preliminary standards on radon flux. And I really haven't
heard anything at all about that.
MR. RATHBUN: I would just say that when I measure radon flux, I do it
with an M-ll, and when I want them calibrated I just send them to Andy George.
(Laughter. )
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MR. GEORGE: I guess you want to put me on the spot again. Well, we have
been doing radon flux on and off, but we really don't do it on a regular
basis. We tried both the accumulation method and the radon flux canister:
Both methods work equally well. If you want data in a hurry, you do the
accumulation method because you can do it on the spot. All you need is a can
you turn upside down. You invert it over the soil with a couple of vials and
let it emanate for maybe a half hour, no longer than two hours or you get into
problems. You start building the radon in the can and then start pushing that
into the soil, but you have to be careful. In our experiments with this, we
found that for different size cans the time that you can allow for this
build-up varies. So, we usually limit it to two hours. From soils, two hours
is sufficient to accumulate enough radon, then you can transfer it to a Lucas-
type flask and count in the laboratory, and then after that release' the flux.
Now, on the other hand, the canister is a very convenient tool, but you
need a much longer time for accumulation, usually, on the soils, something on
the order of 24 hours. From the surfaces and the concrete basements or the
walls, you need approximately 48 to 60 hours. In both cases it works fairly
well, and canisters can be shipped back and forth very easily. In our
experiments, we found that if you seal them after you take them apart from an
illumination area you do not lose any radon. We counted them immediately
after we moved them and then we sealed them and counted them over several days
after we closed them up. We found no loss of radon. The reduction you see is
sort of a decay of radon. So, they both work well, and you can measure almost
any surface with these two techniques. There is no limit with this.
Sensitivity, as I said, with the charcoal canister is about two-tenths to the
minus eighteen curies per centimeter squared per second. I don't know what
EPA is using as a standard, but I think one of the numbers they mentioned was
like two hundred times the minus eighteen curies per centimeter square per
second, after you clean up the tailings. Now, we found numbers higher than
that in soils in the United States. That's background soils. They can go up
as far as 500, with averages about 200 to 300 over an entire year. So, I
don't know whether that is above background or is just 200; I don't know what
the standard is. Does anybody know the answer to that?
MR. BERNHARDT: In response to your question, the proposed number right
now is two picocuries per meter squared per second. It is within the observed
background values, yes. I think it's intended to be excess above that.
Could I just make a couple of comments on what we have done on flux
measurements? I don't have a lot to add to what Andy George says. The main
thing we have used in Las Vegas is the accumulation technique. I guess I'll
note that when you're applying it more to a research thing or trying to put
more effort in I like the concept of taking several accumulation points so you
plot a slope of the accumulation in the vessel and you get a slope-type thing
versus just a single accumulation point.
We've done a little bit with the charcoal cartridges to get comparison.
The comparisons have been reasonable. We really haven't pursued it as far as
we would like. I guess agreeing with your concept of a problem, the
accumulation vessel is only good for periods of like an hour to two hours at
the most. It is hard even, therefore, to compare that to a charcoal
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cartridge. I've compared them over the same periods of time, but you're
pushing the sensitivity of the charcoal cartridge by trying to only do the
charcoal for several hours. It's difficult to do an accurate accumulation
over the one week period that you need for the charcoal. So, to get a direct
comparison is a bit difficult, but it's not impossible.
MR. GEORGE: Now, as far as comparing these two methods, we do have a
radioactive concrete, with which you can do this kind of an experiment. It's
a very homogeneous mixture, and it's big enough to use flux cans and
canisters, and then you can remove the canisters. You can take your samples
with the can and then remove the canisters at different times, and you can
determine this kind of a relationship between the two. I agree with you; it's
very difficult. In the field one time we had to stay overnight to remove
canisters and take the flux can measurements, taking a measurement every two
hours. You have to identify a whole area and place different cans every so
many hours. That's how we found out that you cannot exceed, let's say, in
this area, five hours. You start leveling off and you're getting out of
linearity.
MR. COLLE: An alternative to sending it to Andy that seems to us to be
quite feasible would be to actually develop the relatively small artifact
standard for radon flux, which would be a physical surface that would not be
too large, that literally could be sent to various laboratories for their own
standard. We've looked into this in a preliminary way, and, although a lot of
development work has to be done, it seems that it is quite feasible and that
it would have a dynamic range over which it would work and that one could
literally dope this. It would be a ceramic material of perhaps a meter by a
meter. Thickness is somewhat indeterminable, but it would be impermeable on
five sides. The exhaling surface is only on one side and you would only be
allowed to use an inner portion of the surface area. It would be suitable for
charcoal canisters or for small accumulators; and it would have a dynamic
range under which it would work.
We have considered this quite extensively. If someone would like to talk
to us sometime about perhaps picking it up, developing it on your own, we'd be
quite willing to talk to you about it. It does seem like it's feasible.
MR. ROESSLER: I'm surprised we haven't heard from either Chick or Sam
Windham about this whole question of flux. It's true that both the
accumulators and the charcoal cartridges do a pretty good job of measuring the
flux that occurred during the time interval for which the device was deployed,
or if you're doing successive sampling you can sample a week and get a good
measurement for a week. But the real question is whether this is a useful
number for us because of the temporal variation that by hour, by day, by week,
whatever, seasonal variations. Usually, the meaningful parameter for
evaluating, in our case, a piece of reclaimed phosphate land or some other
situation is the long-term average. And we can't think of anything short of a
long-term sampling experiment to tell us what the long-term average is. So
that's the real problem as far as I can see. What is a measurement that tells
us what the long-term average flux is? These sorts of measurements don't seem
to be that unless you repeat them over long time intervals. The question
probably is, then, is there some other parameter that's more stable with time?
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MR. KEEFE: One of the problems that has perplexed me for quite a while is
the problem of plate out, which I've mentioned before. The most disturbing
part of it is the inconsistency of the various different answers I get from
different laboratories and different people. It seems as though there are a
thousand different answers as to what effect humidity, temperature, charge and
so on have on plate out. I think that's an area that needs to be tied down
before we can develop good instruments that will accurately measure working
levels of radon daughters.
MR. GEORGE: I wanted to say something about plate out in the design of
instrumentation. Our experience so far shows that plate out is only related
to the number of particles in the air. Our experiment (we have a paper on it
in Health Physics coming out soon) shows that if you can measure the particle
concentration in the room, you can almost predict plate out exactly from
theory. All you have to do to test if there is any plate out effect with your
instrumentation is to take your instrument, put it in a calibration chamber,
generate a known particle concentration and, if possible, a known particle
size, and then repeat this experiment with your instrument at different
concentrations and go from high to low. If you see any reduction in your
measurement, let's say of working level, then you know you have plate out. If
you have no reduction, then you can assume you have no plate out. I suggest
that it is one way of testing for plate out effects. As a matter of fact,
every time we design an instrument we go down to five thousand particles per
CC because I don't think you're going to find many atmospheres with particle
concentration less than five thousand particles per CC. So I consider that a
lower limit of particle concentration to which you should subject your
instrument. I don't know whether you can do that in the mine because you have
to have a filter to make sure that if you want to test for low particles you
have to filter the air and perhaps inject some known aerosol concentration so
you can maintain your chamber at the same level for some time until you get
reasonable results.
In a chamber this can be done very easily. You can put in an absolute
filter and then you can inject your aerosol, and you can control it very
easily. Particle concentrations from five thousand to a hundred thousand are
very typical. And I think most of our data show that you begin to get some
plate out in some instruments that we've seen around between five and ten
thousand particles per CC. About ten thousand we couldn't see plate out in
any instrument. So if you can do that, I think it's a beginning. If you can
check it around five and ten thousand and you don't get a plate out effect,
you can almost forget about it. But if you want to be really scientific, go
down to five thousand or maybe three thousand. Then you can argue with
everybody.
MR. GROER: Jim Gingrich.
MR. GINGRICH: I thought it might be interesting to set something in
perspective. You all have read some of the Three Mile Island accident
analyses and so forth that indicate a very low potential number of deaths from
the Three Mile Island accident. Right now, based on very limited data—and
it's obviously very limited—on eastern Pennsylvania, we have about 15 percent
of the homes giving radon values above 20 picocuries per liter. If you
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convert that to working levels (again, above .1 working level) and use the
same criteria that were used for the number of people in the area around Three
Mile Island and assume that 15 percent of the homes have radon levels of this
magnitude, you can see that the potential lung cancer deaths are rather large.
MR. GROER: Thank you very much, Jim. It is a very interesting slide, but
I feel very strongly we should stay out of the area of epidemiology. There
are very special meetings for this sort of thing. Please don't take me;wrong,
but I think we should stay out of epidemiology. There's a meeting, as a
matter of fact, coming up in October in Golden. Many of you know that. So
there will be some discussions on this very topic.
Every one of our panelists has had a chance to comment. I'm coming back
again to the audience. Any hot items you would like to see discussed,
questions?
MR. TOOHEY: This isn't a very hot item or question, but it's something
that you might be interested in. And that is, if you want to take grab
samples of radon in houses, how do you do it? Normally what we've done in the
past is we take a Lucas cell out and have somebody bring it back to the lab
and count it. Well, that's nice if you're doing a hundred or so houses as
we've done before. But in the next step in our study of ambient radon levels
in Chicago area houses, we want to do between three and five thousand; namely,
by giving everybody who works at Argonne a sampling device to take home, take
an air sample and bring it back in. So we need something that's fairly
rugged, will hold a vacuum, and is also cheap. And what we have come up with
are these things, which you can pass around if you want to look at them.
They're basically aerosol paint cans, and they're 80 cents apiece. I
don't know exactly what their volume is. My guess is it's about three-tenths
of a liter or something. We get them from a factory; they say they are
evacuated. We've measured that they only get them down to about 40
millibars. So we pump them down to almost zero. We take them into a house,
give them to somebody, and just tell them, "Hold it in the middle of the
living room, press the button." Instead of something coming out like it does
in your normal aerosol can, something goes in. We then take them back to the
lab, hook it up to an evacuated Lucas flask, let the two equilibrate, and then
count the Lucas flask as normally.
This week is our first real test of these things under more or less field
conditions. We filled four of them yesterday over at Ed's chamber at EERF.
He's going to fill another four of them tomorrow for me. I'll take them back
with me and we'll count them next week and I'll let you know how well they
worked.
UNIDENTIFIED SPEAKER: How do you hook them up?
MR. TOOHEY: To what, the Lucas? The cylinder? Okay. Well, I'm glad you
asked that question, Senator. We have another transfer device. This end will
simply connect to the Lucas chamber somehow, with a shorter piece of pipe, of
course. I brought this one down to hook up to the chamber. On the other end
there's a piece of brass tubing inside a little Tygon sleeve. We take the
button off of them. This just fits over the needle valve on here, you depress
that, and it will hold it down and they equilibrate that way. We did these on
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a sampling port at the chamber, just by hooking the tube up and then slipping
them over and pushing it down. We are making the assumption, which we'll test
when we count them, that the valve wasn't depressed until it was actually in
contact with the radon atmosphere.
But, as you probably know, Lucas cells are kind of expensive. They're
fairly sturdy but not all that sturdy, especially around the windows; and they
don't hold a vacuum for more than a couple of days. So we hope this will
solve some of our problem with it. Maybe by the next time any of us get
together I'll have some data on just how well they work. And maybe we'll put
a note on something fairly brief on it in Health Physics or something. But we
think this is one way we're going to have of doing a lot of grab sampling
fairly conveniently.
MR. COLLE: I just have a question, and it's something that we have been
burned on ourselves relatively recently. I seriously question when you hook
up this can to the cell whether you're indeed going to get first mixing and
then any type of equilibration. I really wonder if that's going to work.
Before you go out making five thousand, I suggest that you check that
transfer, because those transfers are more difficult than they appear on first
appearances.
MR. TOOHEY: On, I agree completely. That's one of the reasons I brought
them down this week. A twofold thing. First of all, see how well they hold
up under field conditions. We presumably will know the concentration in the
chamber. Sue Fisenne also took some samples in the bomb-type devices and some
other samples have been taken. So we'll have a pretty good handle on what the
concentration was and then we'll see what we get. So, maybe they will work;
maybe they won't.
Certainly we will validate the technique before we go into the sampling.
But that's another year down the pike probably.
MR. PRICHARD: Is there some particular reason you chose to go this route
rather than, say, traditional plastic bag of some size which could then be
blown up and returned to the laboratory for, well, possibly even concentrated
techniques? Here it looks like your effective sample size is going to be
somewhat less than 100 ML, accounting for the partial pressure.
MR. TOOHEY: That's probably true. The primary reason is to do it
extremely simply. We don't have to send somebody out with these things to
take the sample. It's a difficult question of what it is you want to do.
Granted, grab sampling has its limitations. We all know about diurnal
variations, this, that, and the other thing. Arthur Scott will tell us
tomorrow maybe how to use grab sampling to decide what to do.
But we thought the first thing we should do is just get at least, one,
preferably several air samples out of a lot of homes and see what we've got
out there—because we've been surprised by what we've seen so far in a few
homes. The highest we've seen is about 60 picocuries per liter. But, 10, 20,
30, is becoming kind of common.
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This is a first stage of the project. Then we want to look at this and
decide how to do a more accurate measurement if need be, or more houses if
need be. And look at some other things. What really determined the level of
the house? We're tending right now to think it's the geological
characteristics of the soil underneath it.
MR. PRICHARD: Well, I agree with your goal of doing some preliminary grab
samples. I may be missing something, but I don't see what's so difficult
about sending people home with a bag of some sort to blow up, especially when
you consider your potential problems with loss of vacuum or transfer problems.
MR. TOOHEY Well, I'm not that familiar with the bag technique, so I can't
really comment on it. But it seems to me that there would be a lot more
problems there than handing somebody an aerosol can, which he's already
familiar with, whether it was paint or bug spray or whatever, and saying,
"Just hold it up and push the button."
MR. COHEN: You have a volume 95 aquarium pump and a $12 bag—have them
taped together—and tell them to put the plug in the wall and leave it there
for five minutes and pull the plug out of the wall and that's the end.
MR. AKERBLOM: I would go back to a topic that we discussed earlier, the
reliability of instruments. When you buy different field instruments—track
etch, meters for measuring, you are rarely told how they react to humidity,
temperature, and so on. I think that we should go together and actually tell
the producers of the equipment that if they sell us the equipment they have to
tell us much more. We have found it very difficult to get such information
from producers. We tried in South Africa to get some figures on the Rowak
caps. They haven't given them yet. They say they work. Okay. They work.
But how?
MR. GROER: Okay. Any manufacturers here who want to comment on this?
(Laughter.)
MR. COLLE: I think the presumption was made that the manufacturer knows
and is not telling you. In fact, the manufacturer does not know. I mean,
most of the instruments that are manufactured were usually developed by
someone like EML, in which case they got the specifications, mass produced
them, wrote up a sheet for it and a price list, and distributed them. And
that's the extent of what they know about them.
MR. AKERBLOM: Yes, that is perfectly true. They don't know. But they
don't seem to test it either. They should have their instruments tested
before they sell them. I found this with track etch. We had to start in
Sweden to test the track etch. The manufacturing company should know if it
was good enough. If we do not put pressure on the manufacturers, we never
have any good instruments.
MR. GINGRICH: I guess one of the comments from our end of the line is
that we welcome questions of any kind. Quite often people will ask us
questions after they've been using our services for a while, not knowing that
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we may have already solved that problem for somebody else. So if you've got
questions about our devices or how to use them, we would more than welcome any
kind of communication and questions that may come up. There are still a lot
of things we don't know and would be happy to admit it.
MR. GROER: Silence? I'd like to bring the discussion then to one
question that has arisen for me. All the methods assume, among other things,
that once a radon daughter atom or aerosol particle attaches to the filter
that it really stays there. Is that really so? What do you people here think?
I'm referring especially to a paper by Johanson. Some people have
probably read this paper. Arid I was really soliciting comments on this paper.
Bob?
MR. HOLUB: I think he concludes that nothing really gets out. If it
does, it's in a vacuum.
MR. GROER: Yes, that's one point. This paper refers to a study in
vacuum. Now, my experience has been that in air I have no evidence that
daughters are leaving without being asked. So, once they're in the filter
they stay there. I have a very poor understanding of the mechanism by which
filters work. I'm thinking of membrane filters. I thought that it might be
worthwhile to get into this if there's interest.
MR. HOLUB: The University of Illinois, similar to Dr. Postadorf"s group
in Germany, is now examining the possibility of reentry from rough surfaces,
whether it's grass or rocks sticking from the wall in a mine, into the
airstream after recall. So it's definitely not very serious, and it's related
to this problem. But the assumption for these studies is that there must be
an airflow because other people already found out that if you have just recall
then it simply returns to the surface where it was before.
MR. GROER: Okay. Well, there seems to be then a universal agreement, in
the absence of any other comments, that daughters do not leave the filter.
Okay. Then, maybe I can go on to the next assumption that concerns me—
constancy. Now, I'm turning directly to Bob. I know that some years ago,
three or four years ago, you started an investigation into time dependent
concentration during the time of sampling. In one of the papers I wrote it
said, "Bob Holub, private communication." Have you followed this subject?
Where does the matter stand?
MR. HOLUB: I'm very sorry. It's still lying on the desk and nothing
happened.
MR. GROER: Okay.
MR. SCOTT: Some years ago I did a study on atmospheric radioactivity, and
this was piggybacked onto an atmospheric dust collection thing. The results
then were somewhat disappointing because these measurements, because they're
collecting dust, have to take place over about an hour at least. There were
evidently changes in concentration there, and, despite analyzing everything
with a multi-Z-squares fit program, we got nonsense answers out of it. This
was particularly true if the radium A concentration increased near the end of
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sampling, because you then got radium A being one quarter of the concentration
of atmospheric radium C or B. So, it's hard to say how large an effect it may
have, but certainly if it does vary, it does make a large effect.
MR. GROER: Okay. Thank you very much. It is obvious that to evaluate
this really quantitatively, by measurement, is impossible, because all of the
methods you have assume constancy, and, if you want to check constancy, which
methods are you going to use to do that? So, it has to be done indirectly.
And I have seen instances where this assumption was certainly not true. One
way of checking is to count while you are sampling. In this case we put the
detector—it was a surface detector—underneath the filter paper. If the
concentration is constant, then the radium A count you observe, say, during
the first minute of a two-minute sampling to the count to observe in the
second minute should be a certain ratio, within, of course, statistical
fluctuations. If that ratio is not what it should be, assuming you take
proper care of the statistics, then I think you have an indication that this
assumption is not true. So that's what we have done in this area.
So what this means to me, and I think you will agree with that, is that
there should be a trend to go to smaller instead of larger sampling times when
you want to measure low concentrations. If you agree with that, I'll go on to
something else. Okay.
MR. COHEN: This is a practical question. If the detector is underneath
the filter paper, what supports the filter paper? The filter, I mean.
MR. GROER: If the flow rate is not too high, sometimes you don't need a
support for this. Filter paper is really a plastic material. Now, sometimes
you can support it with a grade of a certain reasonable mesh size. So, you
lose a little bit of detection efficiency, but it doesn't really make much
difference.
MR. KAHN: You could certainly test this, if you had two collectors, by
offsetting the collection by a minute or two. See what happens then.
MR. GROER: Good point. I think maybe I don't quite understand you, but
the problem there would be, can the two collectors be exactly at the same
place in space?
MR. KAHN: Obviously not.
MR. GROER: Right.
MR. KAHN: As a matter of fact, if they were in the same place or pretty
close to the same place, they may tend to interfere with each other regarding
the air pull. But, if they did seem to be consistently similar, even though
they were a couple of meters apart, that would reassure you.
MR. GROER: I agree with that. We've tried to do it in one place, and
that's the only way I could think of looking at the ratio. Any more comments
on that?
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MR. NAZAROFF: It seems to me that there are two possible time trends that
you would be interested in. In one case, if the fluctuations are of a fairly
high frequency compared to the period in which you're measuring and there is
no long frequency bias (I can't say this with total assurance, but it's my
impression), it won't make very much difference in your analysis procedure.
That is, if you collect a lot of radium A now and don't collect any for a
second interval, then a lot and then a little and then a lot, and there are
many of these intervals during your collection period, you are getting to the
point of talking about discrete atoms—if you take it down to fine enough time
periods.
The second sort of case where you would get into trouble is when the
period is of the same order or greater than your sampling period. Some
evidence can be gained in that question by making rapid successive
measurements of radon daughters at one place. If you do that and see big
differences over a fairly short period of time, then you begin to suspect that
maybe this is going to be a significant problem.
I've done this sort of thing in one house, but the measurements were only
made at 40 minute intervals. I could see trends of longer frequency than
that, and they were not sufficiently rapid to indicate that there would be a
problem with it. I guess that doesn't conclude that there couldn't have been
things going on in shorter time intervals that could have caused the problem.
MR. SCOTT: Maybe I could comment on this question of fluctuation in time
periods. The important question really is, "Under what circumstances are you
measuring?" If you're measuring outside, then we would know what the
frequency distribution of fluctuations in the atmosphere is. If you're
measuring inside, we have a totally different spectrum of frequency—a totally
different spectrum of frequency variation.
Now, given that our main interests, and I'll make an assumption here that
we are measuring inside, we know that we have an effective filtering mechanism
which cuts out the shortest periods of all. So the real question is, "Are our
sample times sufficiently short that we do not expect there to be a
significant variation?" We have done measurements with the Nork gas tracers,
with spot samples as short as 30 second intervals; and you can show that in a
house there are indeed fluctuations of the order of 30 seconds. But, in fact,
the major fluctuations are of a considerably longer period than that.
A continuous radon monitor run so as to give repeated spot samples
demonstrates that in a house there can be significant changes of concentration
in a period of a half hour. In a room with a radon source in it the radon can
change by a considerable number of percent in as short a period as five
minutes. Now, we do have an advantage by measuring daughters in that things
are averaged to some extent because the daughters we measure now are not due
to the radon that is in the room now but due to the radon that was in the room
ten minutes ago, 20 minutes ago, 30 minutes ago.
So, I suspect that if you don't put your sampling period much over about
five minutes—and, in fact, I would raise another question, Why would anyone
measure for more than five minutes?—that is quite adequate sensitivity. The
problem is not likely to be of great significance indoors.
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MR. GROER: Did you say the problem will not be of great significance
indoors?
MR. SCOTT: I think so.
MR. KEEFE: In some of the measurements that we've made inside the home at
Argonne, you can definitely see the effects from an air conditioner fan
turning on. (We take measurements every ten minutes or so. We take grab
samples with a nine minute measuring cycle, with a three minute pumping time
or sampling time every ten minutes.) Up goes the radium A concentration and
the equilibrium shifts. I suspect you can see as much just by somebody
opening the door, disturbing the equilibrium in a home. If you have these
instruments in a home and you are making measurements, I suspect that you're
going to see the effects of a change in the equilibrium concentration of the
radon daughters during that three minute time.
MR. HOLUB: What we propose is simply to simulate it—make a step function
first, of the sampling and then nothing, and do it numerically. The Canadians,
the group in Toronto, did something like that last year. Of course, it makes
a difference, increases the error of all these methods. I forgot exactly how
much.
MR. GROER: Thank you. I think those of us who are inclined to modeling
and playing around with the numbers should really try to get at least a
feeling for what happens if the concentration changes during the time of
sampling. There were some experiments, but, as far as I know, maybe with the
exception of this Canadian attempt, nobody has tried to get a quantitative
feeling via modeling this effect. Maybe I'm wrong.
MR. SCOTT: As a matter of fact, I'm working on that now.
MR. GROER: Thank you. Any more comments on this matter?
MR. PRICHARD: While certainly not ignoring some of the interesting
computational problems that would be introduced by changes in the daughter
concentrations or equilibriums while you are sampling, I don't think I'd be in
any danger of violating your suggestion that we not get into epidemiology by
pointing out that the real bottom line in all the measurements we're taking
does relate to long-term averages. You know, lifetime exposures to people.
The end thrust of all our computations should be those measurements which help
us determine those life-long averages. While there are many interesting and,
in fact, fascinating technical problems, I would not want to see us lose sight
of the forest on account of the trees, let alone the branches.
MR. GROER: Thank you, Howard, for this comment. Although I don't want to
get into epidemiology, it is the working level months that are of concern. In
the same vein, let me point out that there's another problem. The question
is: Over what period of time—and after this I would like to leave this
topic—should you integrate the exposure a miner gets? Should you integrate
until the cancer was diagnosed, five years before the cancer was diagnosed,
ten years before that? That's really a problem that has to do with
carcinogenesis, and that's not solved at this moment. But I agree that
epidemiology is based on accumulative measures. So there's no doubt about it.
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Okay. Now, on epidemiology, any comments? If not, time is getting
short. I would like to give the panelists one last opportunity to express
their views, if they wish to do so. I will start again on this side of the
table. Thank you very much.
(Whereupon, the meeting was adjourned at 5:20 p.m.)
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OPEN DISCUSSION II: AUGUST 28, 1981
Open Discussion; Measurements and Related Topics
Moderator; Arthur Scott
Panel; Speakers for Measurements and Related Topics
Richard E. Toohey
William W. Nazaroff
R. A. Washington
Charles T. Hess
Bernd Kahn
Carole Wilson
Gustav Akerblom
Andreas George
Stephen Rudnick
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PROCEEDINGS
MR. PHILLIPS: The moderator for the discussion this afternoon is Arthur
Scott. I'm sure Arthur by now needs no introduction, but I do have to tell
you my favorite Arthur Scottism I heard him say once and I've thought a lot
about during the last couple of days. He said, "The subtle things we see
right away; it's the obvious that takes us so much time."
MR. SCOTT: Well, good afternoon and welcome. I see there are almost more
people up here than there are in the audience. Nonetheless, I'm sure the
panelists will do their best.
Now, the purpose of a moderator in nuclear physics is to slow down the
neutrons so that they can interact with uranium, and I suspect the purpose of
a moderator in a circumstance like this is to slow down ideas so that they can
plummet into the fertile minds and imaginations of the members of the panel.
There are some questions left over from this morning. So, it would seem to be
a good idea if we started with questions. As moderator, I will take advantage
of my position by starting off with a question statement, and I'd like to
direct this to our Swedish colleagues who were speaking of introducing
regulations for building.
Now, I happen to have had some experience with this, and I would be
interested to hear what answers they have on two points. One of them is:
What mechanism is to be set up to verify that the buildings indeed do meet a
particular standard? Second: What is to happen if the building does not meet
it? I'm dealing with new construction here. What mechanism is to be set up
to check the houses?
MR. AKERBLOM: Well, there has been a long discussion within the Radon
Commission in Sweden on how you should go on with this. What should be the
standard and how should you actually tell people that they are below the
standard limit or over the standard limit. We found out that there was no
easy way to do measurements in houses and get the correct answer. You have
also shown that today. You can't go in and take grab samples, and you can't
actually rely on track etch films to give you a good answer, especially if you
are measuring both radon daughters and radon at the same time.
We know enough to say, "This is regarded to be dangerous to people living
in houses like this; something should be done about it." Should we be
concerned about the exact number? Or could we say that in an area which
exceeds approximately such-and-such amount of radon daughter concentrations,
we would not allow people to live? In Sweden the amount considered
uninhabitable is 400 Becquerels per cubic meter.
But whose definition of danger do we accept? It's not we who are
measuring—we can only give our figures to the people who are working with
it. We measure as well as we can. Should we be measuring more? It costs a
lot. You do seven measurements the whole time, and still you wouldn't be
sure, although much more sure than when you have done it. We have seen
Scott's excellent work, yet he doesn't know everything. It's not low, it's
not high.
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No, you leave it to the health authorities. And tell them, "This is in a
level where we think it's high; it's proved it's higher than it should be
anyhow." And, if you measured over that level, you'd declare that place
unsanitary. Once it is declared unsanitary, they have the means to go to the
house owner and say, "This place is unsanitary." If he owns the house
himself, he can do something about it. Perhaps he can just let it be. The
laws are not so hard on that. But, if he's got children there, you can always
start arguing with him about the risks for the children, and, in Sweden, where
child advocacy is strong, it is not just his problem. The country also has to
take into account the risks for the children. If he's renting the house to
somebody else, of course, it's an easy thing. Because then he has to do
something about it or he can't rent it out.
But this has been a discussion of people not willing to do something. And
this will be difficult for a long time. Until now we have not met up with
anyone who says, "I don't want to do this." "I don't want to follow your
instructions." They are happy to know that you can do something to the
houses. And you could tell them to enforce the ventilation in the house where
concrete is used. But that would be a simple solution. But, if you were in a
house where it comes from the ground, it's more difficult; it costs you quite
a lot. So to give them a start, the State has provided loans for people who
want to do something to their houses. The problem is, of course, that you
don't actually know what to do. This is going to take some time. But we are
coming out with some advisements which, I think, will be successful. They
have been working in Canada, and I think they will also be working in Sweden.
Did I answer that question?
MR. SCOTT: Yes. Thank you. For the people who have just joined us, we
are still beating the questions on this morning's session. If anyone does
have any questions, would you please quest. Yes. The first one to the
microphone gets it.
MR. RATHBUN: I just have a comment on the last presentation of the
morning session, Mr. Washington's presentation. He was talking about the
possibility of going to lithium fluoride dosimeters as opposed to the calcium
flouride-dysprosium which he's now using. I would suggest that's not a good
step since I had to go the other direction. You'll find that the calcium
flouride-dysprosium has at least 30 times better sensitivity for gamma, which
you're not really interested in, but it also has considerably better
sensitivity for alpha, which you are interested in.
I used a .015 thickness, which is thinner than most TLD's that you get.
Also, concerning the nonlinearity of the calibration factors, I also found
this. But I found it to be much more pronounced at high levels than I did at
low levels.
MR. KAHN: In connection with this, have you checked on the intrinsic beta
background of the cans, just to see whether there would be a zero, non-zero
reading?
MR. RATHBUN: Yes. Of course, I used a background dosimeter and always
subtracted the difference out.
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MR. KAHN: But they're not outside, are they? They wouldn't be exposed to
the surface of the can.
MR. RATHBUN: They're not, of course, in the ionization chamber with the
other chips, although I have run some right in the ionization chamber—but not
on the probe. I found that the background measurement isn't much different
above the case of the perm or below it or beside it. The place I had the
biggest problem was unfortunately on one of our probes. It's designed to hold
two background dosimeters on the side, and they are in a different plane, of
course, 90 degrees out from the active dosimeters, so they don't get as much
background if you stand them on edge like that. But, as long as you keep them
flat, you're okay.
MR. KAHN: Well, I was just thinking that if there was a base background
due to anything within the ionization chamber itself, that obviously would
cause the curve to go, not to zero, but to the positive number.
MR. RATHBUN: Yes, I think if you use the background chip, you'll subtract
out not only the gamma, but also the beta.
MR. GINGRICH: Back again to Mr. Washington's paper of this morning. I
spent some time with the Australian Radiation Lab a couple months ago, and
they had done a rather thorough electrostatic field evaluation of that
particular device and came to the conclusion that most of the problem of the
huge variability of the device was due to the placement of the TLD in the
electrostatic field. They did not feel that that device would give them the
kind of confidence that they wanted in making the measurements there. They
had done quite a bit of testing on it.
MR. SCOTT: First one to the microphone gets it.
MR. PHILLIPS: This is to Richard Toohey. I've seen those slides before
on the equilibrium values. Have you verified those values, using any
different instrumentation than the two you described this morning? I think,
namely, you are looking at radon with the Wrenn chamber and the working level
with the Environmental Working Level Meter.
MR. TOOHEY: Yes and no. The Wrenn chambers are. We always take a few
Lucas flask grab samples, and they seem to work pretty well. But we have not
used another device to cross calibrate or check the working level monitor.
MR. PHILLIPS: Thank you.
MR. SCOTT: I'd just like to add a comment to this. First of all, the
working level—equilibrium fraction ratio, rather—is defined as 100 times
working level over a radon for a co-existing concentration. So, in fact,
under normal circumstances, no parent measurements actually measure
equilibrium fraction—because it is extremely rare for people to take air
through a filter and put it into a plastic bag and then take the radon sample
from the plastic bag.
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So, we in fact are bedeviled in this question by a further source of
variability. First of all, there's the spatial variability because you're not
measuring the same space; and, secondly, the sample times are so far
different. I mean, take a short sample of two minutes. It only takes a
matter of a second or so to fill a Lucas flask. And, your sampling theory
says that, your estimate must be different.
MR. TOOHEY: I agree completely. In fact, it's worse than that. We found
that our particular Wrenn chamber takes about an hour to come to equilibrium
with an external radon concentration. Most of the measurements I showed were
hour-long counts. So, obviously, we're seeing an hour-long average, whereas
the working level monitor takes a two or three minute sample and counts for
ten minutes or whatever it is. This is certainly a source of some of the
variability we see. But I think on a long-term average, hopefully, that will
even out.
MR. PHILLIPS: I'm aware of all that. I guess the thing that disturbs me
about some of that data is the extremely low radium A values when compared to
the radon.
MR. TOOHEY: Well, most of it is on the surfaces. We have made the
measurements, and we can show that the missing radium A has, in fact, plated
out.
MR. PHILLIPS: I've just never observed that, I guess. If I make
simultaneous radon and working level measurements in a room, I see a lot
closer equilibrium of radium A to radon—in any situation.
MR. SCOTT: We had a number of papers this morning that touched on the
topic of plate out generally. Is there anybody else who is interested in
plate out or would like to say something about it? Mr. Holub?
MR. HOLUB: I have to say something about the fan, obviously. There was
an additional up-date paper on plate out published in a proceedings from the
University of Illinois in 1979. I can send a copy of the proceedings to
anyone who's interested. The reason we did this was simply to try to
understand better what is happening. The first thing one has to look at is
the condensation nuclei concentration—its size, of course, its charge,
humidity, and perhaps even the chemical character, of the condensation
nuclei—and then try to guess the mechanism. So, for instance, it's much more
likely that small condensation nuclei would stick to the fan rather than the
big ones, which might bounce off because of inertia effects.
Then also there is the charge or even image charge on the blades. We have
explained it in our paper—we had put charge on the blades and it affected the
sticking. Then there is the big question of what are the sticking
coefficients, because the typical aerosol phycisist always insists it's one.
But there is now growing evidence from other sources—the Indians measured it,
and certainly Hopkie measured it, and Krugar in South Africa—that the
sticking coefficient is much less than one.
All this says that one should be careful about assuming what's on the fan
and what's on the wall. It depends on many things. So I would somewhat take
exception to calling it an artifact. It's the most natural thing.
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MR. SCOTT: And what is probably a concluding comment on this, I've been
looking at this question of deposition, too, by measuring deposited activity
on the walls of buildings. This is a field measurement, not a laboratory
measurement. It is difficult because if one uses an ordinary alpha
scintillation counter your sensitivity isn't that great. But, nonetheless, we
do have a few places where the radon concentration is high, and we're able to
demonstrate from this a little bit of theory that, in fact, deposition
velocities for unattached daughters are in the region of .1 to .5 centimeters
per second, which is what we measured, and will, in fact, account for most of
the variation of working level ratios that we actually see in houses. So the
question of squaring the material balance does not seem to be beyond the wit
of man at the moment. The difficulty seems indeed that deposition velocity is
a function of air turbulence—of air velocity over the surfaces. So, as
usual, we were able to replace one fundamental question by an even more
fundamental one.
UNIDENTIFIED SPEAKER: I'd just like to make a comment. I have read your
paper. You were nice enough to send it to me, and, as I recollect, I didn't
refer to it in my write-up, but your deposition rates were about the same as
what I was getting. So, I think there's some agreement.
MR. SCOTT: Are there any more questions arising out of this morning's
presentations?
MR. TOOHEY: I'll follow in our esteemed chairman's footsteps by asking a
question of a co-panelist, and that is Bill Nazaroff. In your paper this
morning you talked about correlating the radon source term with wind speed
measurements. I wanted to know what happens to the radon level. We've seen
essentially no correlation between wind speed and the radon level in a house.
MR. NAZAROFF: For any of you who have been to a meeting with Arthur Scott
before, if he was in this situation, he would pull out a view graph and show
you exactly what had happened, but I'm unfortunately not that well prepared.
We made wind speed measurements in only one house. When you look at the
radon data from that house, you see that when the wind speed increases, the
radon concentration increases slightly and then after a few hours begins to
drop in response to the increased air exchange rate. You could, in principle,
take the figure that I presented and work backwards, but I have the original
data which I would be happy to send you.
MR. GINGRICH: I just want to make a comment about the wind speed thing as
long as we're on that subject again. We made a lot of soil gas measurements
with our track etch cup along with comparing our comparison measurements with
some other techniques. One of the most interesting things we found, and it
may have an application to Bill Nazaroff's problem, is that if you set out a
grid of samples or sample sites in a very hilly area and make soil gas
measurements, if you use a radon emanometer where you're taking grab samples,
you'll find that when the wind is blowing onto the surface of this side of the
hill the radon soil gas levels will be fairly low, in fact, quite low if the
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wind is high. If you then measure over the top of the hill on the opposite
side, the radon levels go up again. This is due to either actual forcing of
the air through the soil on the hill or possibly Bernoulli effects bringing a
lower pressure zone on the other side.
The same thing may be true in these houses. When the wind is blowing on
the house, it could be Bernoulli effects that are helping to bring radon out
of the soil gas and into the house. Also, with regard to other measurements
we've made in soil gas (we've made something like 300,000 soil gas
measurements in different parts of the world), the average we're finding is
about 100 picocuries per liter in the soil gas. But it's not unusual to have
soil gas concentrations ten times this. And that's only 15 to 18 inches below
the surface.
MR. SCOTT: I'd just like to reinforce this. If, in fact, the causation
of high radon levels in a house is due to the pressure in the house being
lower than outside, it's clear that Bernoulli's theorem requires that when the
air blows around the houses, it's got further to go; the pressure inside the
house must be lower. Therefore, the harder the wind blows, the more negative
the house will become relative to some distant point on an infinite plane.
In addition to that, the upwind portion of the house is a positive
pressure on it and the downwind portion of a house has a negative pressure on
it; and these pressure zones do not terminate at the soil. They in fact
extend into the earth to some distance. We have made measurements using an
emanometer around houses of the radon concentration and soil gas and find that
if you can make measurements on the upwind side, at times at a depth of two or
three feet, you get essentially outside air. On the downwind side, you can
get concentrations of perhaps a thousand picocuries per liter, which is
normally the kind of concentration you expect at several feet depth.
The whole situation is incredibly dynamic. Many of the things are not.
Many of the problems are partially aerodynamics, not those of the radium in
soil, per se.
MR. COLLE: One thing puzzles me, I've seen an awful lot of results lately
where people have looked at various correlations to meteorological parameters,
but I don't see how you can find a correlation between radium content, or
radon concentration, and a single variable unless you have some model you're
starting with, since all of the meteorological variables are
cross-correlated. How can you separate out that cross-correlation? I mean,
temperature and pressure are certainly cross-correlated, you know, and wind
speed. In other words, since seldom are all the other variables constant so
that you can really see a correlation between radon and wind speed, I just
don't see what these results mean.
MR. SCOTT: I have a particular bias on this subject. When we started on
our remedial projects, everybody knew certain things were true. After a short
period, I decided that the simplest way of evaluating them was to assume that
everyone was wrong. And we made measurements in adjacent houses for a period
of time and found that readings made within a matter of 15 minutes in adjacent
houses were not correlated. Now, it is conceivable that for a house you could
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develop a set of correlations with wind speed and so on. If, for example,
there is only one hole in the house for radon to come in out of the soil, when
the pressure is high on that side then indeed radon may come in. But that
particular correlation may only apply for that particular house. I would
require a lot of convincing to believe that there is any general correlation
with anything except perhaps the most physical of variables, such as perhaps
wind speed, in the sense that may increase the Bernoulli forces. Though,
unfortunately, it almost invariably leads to an increase in ventilation rates,
so it's hard to see the difference, and perhaps the external temperature
difference.
Presumably we've beaten this one more or less to death. Would anyone like
to change the subject with questions?
MR. BAILEY: I have one general statement to make. I've seen a lot of
times when people amass paired data and then start to do regression analyses,
line fitting least square analyses. I think we need to go further than just
the "R" factor. I think whoever is massaging the data needs to go look at the
standard error of Y on X. It's very easy to take a shotgun blast of data and
find a straight line that fits it very well and assume that there's a good
regression or a good correlation, when it's not necessarily so because the
error of that analysis is very, very broad.
My second comment is directed to either Mr. Akerblom or Ms. Wilson
concerning their limits for new structures of two picocuries per liter. In
our study in the State of Florida, we found houses that are outside of our
district of concern that we used for control structures to be in excess of two
picocuries per liter. From that we assumed that this is sort of like
background for maybe six picocuries per liter radon indoor, being background,
or typical of anywhere. Have studies been done in that area on houses not
presumed to be in the area of concern or houses built with crawl space or
mobile homes or whatever, and, if so, what kinds of indoor radon levels are
there?
MR. SCOTT: On the two picocuries per liter, I think that's two picocuries
per liter equilibrium equivalent radon, or .02 working levels.
MR. BAILEY: Okay. I misunderstood the equilibrium.
MR. SCOTT: A good SI unit there, I think.
MR. AKERBLOM: It is really a problem. This is a very low limit, as I see
it, for radon daughter concentrations inside your houses. When we had the
problem in Sweden, it was decided, based perhaps upon too limited a number of
measurements, that, for health reasons, you couldn't go with a higher dose and
allow it in your houses. I think that is something one of you has to come up
with—what dose will we permit for people living in houses? And, if you have
not decided that, well, you have to do it sometime.
The Canadians have done it from what I understood from you, Mr. Scott, for
houses on tailings. We have done it for houses on ground anywhere. But still
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you might say these are provisional limits, as I see it at least, which may
not be generally applicable. We, in Sweden, had simply come to a point where
we had to impose a limit. It was done before we had full knowledge.
MR. BERNHARDT: Just for clarity, is that net above background or is that
a total gross, two picocuries per liter in equilibrium?
MR. AKERBLOM: It is a total measurement in the house. I think I
misunderstood Mr. Scott's question earlier in the panel. He asked me how we
measured this, and this, of course, is the question. Until now I don't think
anybody has tried to measure this. There has also been discussion about how
it should be measured. They say it's not possible with the equipment that we
now have. So it is possible that one might permit a radon dose of double that
amount before doing anything about it. However, in my opinion, anything over
that amount should be considered an emergency situation requiring immediate
attention.
MR. SCOTT: So, it looks as if we seem to have finished with questions of
this morning's presentation. So I will, again, take advantage of my position
and propose a few questions for the panel. It's always a good idea to start
on a fundamental question, and it strikes me that in the group of people
gathered here we have had people who are worried about making measurements in
mines, people who are making measurements in the atmosphere, people who are
making measurements in houses, and, indeed, there are people who are concerned
about making measurements in laboratories. Many of these people, in fact,
don't have much in common. For example, the question of plate out in sampling
heads is a non-question for probably about 95 percent of all people who take
samples because they use an open-faced filter holder and transfer the sample
to a separate sealer. It's only the sophisticated guys who give themselves
sophisticated problems.
But let's see if I can raise any interest on a fundamental question. We
have an international meeting here on radon-radon progeny measurements.
What's the purpose of the measurements? This is a fundamental question
because it, in fact, raises a lot of questions and also simplifies things a
lot. What purpose are the measurements that we're talking about? Is this a
very general meeting or is there an underlying theme or interest that we
should be pursuing?
MR. HESS: I think that people who measure radon should have a
responsibility for measuring radon in their own area. I think fulfilling this
responsibility can provide information from a wide variety of different
sources of radon, and our picture then of radon levels in the United States
or, for that matter, throughout the world will gradually become clearer.
I must say, I have a lot more enjoyment from measuring specific physical
effects, but I think that if each of us could take it upon ourselves to
measure some local buildings—either private dwellings or factories—and try
to collect more information about what the levels are, we would then have a
more complete picture that would help us determine some of these questions
about levels.
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In my case, I've spent most of my time measuring in Maine, and I have
found that doing one State is more than enough trouble—more than enough
difficulty to keep somebody busy for a long time. I think that as scientists
in this area we have a certain moral responsibility to do some work which will
be of significance, perhaps either for health or for understanding or to
alleviate fears or misconceptions in our own areas.
MR. KAHN: In connection with that, there seems to be now three possible
sources of elevated levels. One is in Maine—and some other places, too, I
guess—where there seems to be a lot of water bringing in high levels of
radon. Certainly in many parts of Sweden there seems to be the underlying
geology of the shell bringing in radon. We've worried about building
materials, but I haven't seen any that are as high as that. Even in Sweden it
seems as if it's underlying material more than the building material.
Probably a systematic way of getting at this is to say, "Well, okay, let's
look at these two areas." Of course, there's also man-made materials being
placed underneath houses. Let's look at these areas from the point of view of
geology, for instance, for high radon water and high radon emanating
materials. Then let's do extensive measurements. How about these places in
Pennsylvania? What's the source there?
MR. GINGRICH: The area in eastern Pennsylvania we've been surveying is a
known uraniferous area. .There are some old uranium mines in the area and some
underlying rocks that are known to contain uranium. It extends not only to
eastern Pennsylvania, but down to New Jersey and a few other places in that
area.
MR. KAHN: I'm sure in Maine, for example, you went at it because you knew
there was a lot of radon coming out of water supplies. So, I think that if we
wanted to go at this from a public health point of view, we'd need first the
kind of thing that's being done in Sweden. I guess we can get at that one of
these days in the United States. The EPA laboratory here has been looking at
radon—how far are we with radon, Chick, in water? Will we within a few years
know where all the high radon levels are in the water?
MR. PHILLIPS: I think we'll have a lot better idea. I think certainly
within a couple of years we'll be able to identify most of the problem areas.
MR. KAHN: Okay, so we may have these four areas. I think a way to go at
it is to not all go at it and measure but to define where these problems are
and then look at the high level areas and the marginal areas.
MS. WILSON: I think, in fact, in the United States here you've got an
awful lot of information that you haven't used yet. I've talked to John Pacer
from Bendix and he says that large areas of the States have been known for
prospecting purposes, and this information has not been used by the
environmentalists. All our radiometric measurements were made for prospecting
purposes. This was material that we had at hand and so we just decided to use
it.
MR. BAILEY: We have had a commercial group do a radiometric survey of the
north end of Florida for mineral mining purposes. In the southern end, the
phosphate region of Florida, we did our own aerial survey for gamma only, just
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gross gamma exposure. There has been a lot of controversy going on between
various groups as to whether or not gamma is a useful indicator of the radon
problem or potential radon problem. We happen to think that gamma is actually
of very little value whatsoever as far as a radon problem, unless the exposure
is well over 25 or 30 microroentgens per hour. Otherwise, it's not much of an
indicator at all as a potential radon exposure problem.
Part of the thing that we're stuck in the middle of—that probably many
other groups are going to be in—is modeling. As in the case of the people
from Sweden, they talk about two picocuries per liter being the maximum
allowed in new residences. One of the things that we are looking for, that
we're trying to do something about, is how can you go to a bare piece of
property that you haven't seen before, except maybe driven past on the
highway, and take a measurement, do a little handwaving and say, "Yes, we'll
have a problem," or, "No, no problem here."? That's one of the problems that
we're really stuck with in the States. It's not measuring it so much or what
to do about it when you find it, because there's nothing you can do about it.
You can't force anybody to spend money on their house. But what do you do
with a piece of property with cows on it that a developer is going to build
houses on? That's the problem that we're stuck in.
MR. RATHBUN: I have a question along that same line. I have sort of lost
track of where we are in the scheme of modeling these days. I know that UDAD
has gone through a certain amount of transition, and I hear people talking
about AIRDOSE and MILLDOSE and I wonder how all these things are related and
what the status is now.
MR. SCOTT: Offhand, it would seem that things like your MILLDOSE and
AIRDOSE are not really particularly relevant to this problem. The difficulty
is not radon coming in from outside, but radon from inside trying to get out.
As to the question of modeling houses, I don't know how far that is along.
Again, there are so many parameters that it's difficult to know where to
start. This indeed is the unsolved mystery. So what impels the stuff to come
in?
MR. BAILEY: This is sort of what I was trying to lead to with the
question to Gustav and Carole. My second question was: Do you have a limit
for a new structure? Do you allow the new house to be built and then go in
and measure it and then say, "Well, you're past the limit, you're going to
have to do something about it."? Or, are you developing a method for looking
at a piece of property and saying, "Most likely remedial action will be
necessary in this type of a structure."? If so, what parameters are you
looking at as flag parameters to decide whether there should be modifications?
MR. AKERBLOM: In fact, we are looking for areas with high radon
concentrations in the soil. It's not only high radon concentrations; it's how
much air is available to get into a house. We need to have some way to tell
if it's a big problem. In my opinion, all houses should be built a little bit
off the ground surface. Even on normal ground radon comes in, as shown today
from many of the reports on ground problems of radon in soil. You have to
really, from the beginning, ask, "Are the building techniques what they should
be? Are they proper to meet the requirements of health inside the houses?"
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These concerns must be impressed upon the people who are building them. You
have to implement some building regulations. Otherwise, we'll have problems
elsewhere. We'll have it there and there and there.
MR. SCOTT: The problem to some extent is probabilistic. If you remember,
I showed a view graph of the distribution of means in Elliot Lake. Now, this
is an area where undoubtedly there is a radon problem by our definition of a
radon problem. On the order of 20 percent of the houses were above .02 WL.
Now, Elliot Lake is a relatively small and compact town. But, suppose we turn
it around. We're saying in fact 80 percent of the houses don't have a
problem. The soil, to all intents and purposes, is the same over this area.
It's about as uniform as you're likely to get anywhere in that kind of area.
It isn't like some areas such as down in Florida where the soil has been
carefully resegregated, and it is probably even more uniform, though high.
Eighty percent of the houses don't have a problem. Interestingly enough, we
have some areas where there's an attempt to do radon proof structures, and 50
percent of the houses have the problem.
So the real difficulty is that there are some subtle effects taking place
in the soil. We've even had different working levels, considerably different
working levels, from one half of a duplex to another. If you cannot get
uniformity over a distance of 20 feet in the parameters that control the entry
of radon into houses, I think it is almost a vain attempt to try and talk of
large areas except in the vaguest of terms.
If you could just paint the curbstone with zinc sulfide and find your way
home at night, it might not be a good area to build on. But, even places that
are essentially at the low end of the scale, less than one picocurie per gram
radium, still have some houses in them that exceed .02 WL on the long-term
average. So, one can only make probabilistic statements. It is well-known,
now, that neither the public nor the regulators understand matters of
probability.
We seem to have drifted off a little bit from the original question, which
was: Is the underlying theme, or has the underlying theme of the meeting
been, environmental-type measurements or measurements in houses, and should
we, if we are thinking about the underlying theme, think about it more,
perhaps? Suppose, in fact, we take for granted that really the main interest
of the meeting has been matters of environmental homes. Then there are a
couple of questions that spring naturally out of this, and one of them is:
Are the current devices you've got good enough? I mean, should we, in fact,
ostracize anyone who comes around for a grant to improve an instrument on the
grounds that he's purely wasting the taxpayers' money? Or, should we, in
fact, say that the present instrumentation is so inadequate that anyone who
comes around proposing action on past measurements should be ostracized
because he clearly can't determine anything useful? Or, indeed, is the
situation in between the two?
Would anyone possibly on the user side like to say something about
instrumentation and its present adequacy?
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MR. HESS: I notice that McDonald Wrenn is not here and Henry Spitz is not
here, so I'll say a few nasty words about Wrenn meters. They have a
difficulty with humidity, which has been written about and published by Andy
George and others. They also have the property that when you set them down
vigorously some of the parts inside come undone. So you need to be somewhat
experienced in repair of equipment in order to make field measurements with
them. I would say that having a rugged electronic device, having one that's
rugged enough to be able to be taken from one lab to another, ought to be one
of the criteria applied before a device is suggested for common use in field
studies; it ought to be able to travel around in an automobile and be bumped
and so on. I guess that's not the usual degree of strength that you'll find
in laboratory equipment at universities. So, "ruggedization," I think, is one
of the things that I'd like to see in some of the equipment. Maybe that makes
it more expensive, but I think it's well worth it.
The other thing that I'd like to encourage people to do is take meters
from one lab to another and try to get multiple calibrations. I've found that
very useful and also I learned a great deal by doing it with the Wrenn meter.
As far as the Track Etch cups go, I think I'm reasonably satisfied with
the way they behave. I would really like to see, though, some type of a track
etch device or something analogous to it that would be perhaps a factor of
three or four cheaper. That would really open up surveys of a thousand
houses, which would be quite nice. If something could be done to have a
reliable detector that works like a track etch detector does but that would
sell for perhaps $5.00 apiece or something like that, then that would be a
very valuable contribution, I would say.
MR. PHILLIPS: I'd be interested in a good passive working level
monitor—one that sells for under a thousand dollars and reads down to .005
working levels.
MR. SCOTT: As a user, I'd be interested in just getting a good reliable
air sampling pump that was small enough and light enough to be carried around
by a five foot two, 18-year-old girl, preferably with blond hair and blue eyes.
(Laughter.)
MR. BAILEY: In following what Arthur was just talking about, a year or
two ago, Mr. Pai, up in the Canadian area, was working on a little,
aquarium-like pump with a track etch intimately placed to a filter system. I
got a letter or two about it, but has it gone anywhere, or has it gone into
the fish tank?
MR. SCOTT: No, no. It's been saved from the fish tank. This is Lynn Pai
of the Ontario Ministry of Labor, which is responsible for radiation
monitoring. What he has is an adaptation of the French CAE nuclear track
dosimeter for working levels. It isn't passive; it's active. That's why the
pump is required. It uses cellulose nitrate film; and the energy sensitivity
of cellulose nitrate is used in this in conjunction with the absorber so that
you can, in fact, get the total number of radium A atoms, radium C prime, and
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also thorium C prime of that deposited on the filter. It's hoped that it will
shortly be put into use in Elliot Lake, as a matter of fact, to monitor new
construction for compliance with the new construction limit of .02 working
levels.
MR. PRICHARD: While we're in the business of wishing for new and improved
equipment, a little gadget I'd like to see on the market-i-please excuse me if
it's there and I haven't seen it—is a simple and rugged and inexpensive pulse
logger. I don't think we have so much a shortage of devices that are capable
of translating an alpha particle into an electronic pulse, but, at least in
the realm of field equipment what I have seen, there is a real shortage of
handy little gadgets to take a pulse and store it until you're ready to ask it
how many pulses it saw.
MR. SCOTT: Well, I was unable to provoke many flights of fantasy there.
In the operational field, and, of course, most people here are not involved in
quite that sense, we do have a continual problem that I touched on this
morning, and that is how well the short-term measurements represent the
long-term situation. Now, to get an annual average you must make measurements
for a year. But one of the topics—if anyone has any views on it I'd like to
hear it discussed—is the question of variability, in the short run. You know,
maybe a few measurements in the best of all possible worlds would be
sufficient to give us an estimate of the long-term average. Can I stimulate
any interest here?
No, clearly not. Well, we've heard one heart-felt cry regarding
calibration and inter-laboratory comparisons. I think everyone who has
participated in one has found it instructive, particularly if they came out in
the middle.
(Laughter.)
Yes. Well, that's useful and instructive. It's instructive if you were
one of the outliers. The general theme seems to be we can't have enough of
them. Would anyone like to comment on those kinds of things? Are there
sufficient numbers of these things? And what about the crude and untutored
users of the majority of a lot of this equipment? I think, particularly, of
people in mines. Is there sufficiently wide publicity given to
intercomparison to persuade them to send in an air pump and sealer? Maybe one
of the laboratory people might say something.
Yes, please.
MR. HOLUB: You mentioned pumps; it is really a bad problem. The best
seems to be a self-regulating device. It costs about $300 and can control its
flow to pressure up to 50 inches of water. We had the best experience with
these. All of the others failed, and this one eventually failed, too, in the
mine. But it was definitely the best. I can provide details on the pump to
anyone who wishes them.
MR. SCOTT: Though, this doesn't quite answer my question.
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MR. HOLUB: Oh, I'm sorry, I thought you asked about the pump.
MR. SCOTT: No, I'm saying, what about the user? It's all very well to
have a good pump, but do the users ever get encouraged to actually send in a
pump and sealer to compare the working levels of the climax mine with the
working levels on your test mine?
MR. HOLUB: Definitely not, no. They don't really care.
MR. SCOTT: Indeed, a question of accuracy in a vacuum, so to speak.
MR. RATHBUN: I think some of this is done, although probably not enough
of it, especially with the air pumps. I formerly worked for the Mine
Enforcement and Safety Administration in Denver, which worked quite closely
with the Bureau of Mines there and the people did send in those pumps and
sealers—all sorts of equipment—to be calibrated by the government.
MR. HOLUB: I have to add that these recommendations are usually ignored.
I am not complaining, just stating.
MR. SCOTT: The reality is, everyone checks. A given organization often
checks its sealer with a source that's been around for five or seven years and
has got someone's initials scratched in on the active side. Unfortunately, it
so often seems there is a tremendous gap between what we know we can do and
what we actually do. But, still, there seems to be no place to get
self-confessions from the assembled multitude.
I see Andy George here sitting pensively, so I would like to direct a
question to Andy. With all the instruments that come walking through his
laboratory, when do you think we will have enough?
MR. GEORGE: I think we have enough already. It's just a matter of
calibrating and using them properly. We have every conceivable instrument
that you need to determine exposure, concentrations, and so on. So I don't
understand why you need to develop any more. We just have to take what we
have and try to do some quality control calibrations and start using them. I
think our immediate goal is to go out and make a lot of measurements to find
out what is the exposure throughout the United States. There are questions to
be resolved. For example, Jim believes geological formations cause the high
levels in Pennsylvania. I don't think so. We found radium concentrations in
soils about 1.2 to 1.5 picocuries per gram. He can hardly say that's
abnormal. So, there must be many, many other locations like that throughout
the United States.
So as far as instrumentation, I think we should go out and take numerous
samples and identify these areas in the country. We do have instrumentation,
if we learn how to use it properly. All the instruments I work with are
usually built in our laboratory and I can vouch for them. But I've seen a lot
of instruments come in that are not working; and they are supposed to be
working. They are off by factors of 2 to maybe 22, as much as that. So it
depends on who builds the instruments and how much he puts into calibrating
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his instruments. As far as I know, no commercial devices have been calibrated
at all. Sometimes they put a calibration factor from theory, but that doesn't
work. For example, when you calibrate an instrument that uses a TLD
dosimeter, you have to calibrate the whole system, including the TLD and
everything. So, when you are using calcium fluoride or lithium fluoride, it
is only as good as you can calibrate it. I mean the whole system—not just
the PERM or the passive device or the active device—has to have the TLD
included. Everything has to be included.
MR. PHILLIPS: I hate to disagree with Andy because he's certainly the
expert. But I don't think we have a working level instrument with which we
can make long-term measurements in a large number of homes without expending
an exorbitant amount of manpower and money. Now, I think we can do it for
radon, but, unfortunately, guides are not set in terms of radon. Even though
we might all say that the equilibrium factor is .5, you still, at some point,
have to measure the working level; and I don't think we have those instruments
yet. At least, I'm not familiar with them.
MR. SCOTT: Would anyone in the audience like to comment on measuring the
environment? Instead of talking, getting out there measuring? Oh, well
here's a surprise, Mr. McGregor.
MR. MCGREGOR: It looks like Arthur is pointing in my direction. It's our
agency that has perhaps made the most extensive use of grab sampling
techniques—and I was quite interested to hear Arthur's comments regarding his
synthetic grab sampling with his replica sampling procedures. To date we have
measured in 19 communities now, and about thirteen and a half thousand homes.
But they're all single measurements. We feel that this has given us some idea
of what the general background levels might be in various communities and
perhaps in various geological environments.
We have also done perhaps another five communities across the country to a
much more limited basis of sampling. But it's rather interesting to hear
Carole Wilson's comments regarding the work in Sweden using the geological
maps that they have prepared for their aerial survey work. We have also noted
in Canada some areas, Castle Guard, British Columbia particularly comes to
mind, where there is a town down the Columbia River called Trail and there is
a definite, significant difference in the average levels of radon and radon
daughters in these two communities. Castle Guard is being affected by a large
uranium potential ore body. It's about .6 percent 0303 up the hillside
which has undergone valley glaciation, at least twice, with the detritus being
deposited in the valley and contributing to the higher levels in Trail—oh,
sorry, in Castle Guard as compared with Trail. This has also been noted in
geological differences in the Bancroft area for radon concentrations in homes
and in northern Saskatchewan.
Speaking of Saskatchewan, there is a study currently underway with the
provincial authorities using the extensive aerial survey maps to try to
delineate high risk areas for radon in the community of northern
Saskatchewan. They are using these maps and then going into the very small
villages and towns and doing house surveys.
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MR. SCOTT: Thank you very much. I think this shows that you can in fact
determine quite a lot if you actually go out and measure, rather than sit
around and think about how best to measure.
MR. AKERBLOM: While I have the opportunity, I want to ask if anyone has
been doing radon measurements in underground homes, which seems to be a
popular way of building homes in the States and is starting to be in Sweden.
But, I think, if you have a problem on the earth's surface, digging yourself
down into it will create a much greater problem. I would be very happy to get
in contact with people who have done actual measurements in underground homes.
MR. TOOHEY: We have done some preliminary measurements; we've done six
underground homes. I don't have the data with me, but I can easily send it to
you. I do have the average with me, which is an arithmetic mean of 4.5
picocuries per liter for the six homes. We also have done some preliminary
work on solar powered homes; specifically, a few which have essentially put a
big rock somewhere in the home as a heat sink and reservoir. In those, we
didn't see much out of the ordinary. But, on the average, the underground
homes have been higher.
MR. SCOTT: Well, as we seem to have run out of inspiration, I think we
will just conclude the meeting so that everyone can get a cup of coffee before
they depart for the laboratory. I'd like to thank all our panelists and all
you participants and turn over the meeting to Chick Phillips for the
concluding remarks.
(Applause.)
MR. PHILLIPS: Thank you, Arthur, and the panelists. I'd just like to
thank all of you for your participation in the meeting, and, particularly, I'd
like to thank Cathy, Marca, and Bob for their assistance.
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