Environmental Monitoring Series
THE STATUS AND QUALITY OF
RADIATION MEASUREMENTS OF WATER
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service. Springfield, Virginia 22161.
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EPA-600/4-76-017
April 1976
THE STATUS AND QUALITY OF RADIATION MEASUREMENTS OF WATER
by
A. N. Jarvis, R. F. Snriecinski, and D. G. Easterly
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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CONTENTS
Page
List of Figures and Tables iv
Introduction 1
Methods and Procedures 3
Preparation of Water Samples 4
Analysis by Participants 5
Results and Discussion 8
APPENDIX. Statistical Calculations 19
iii
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LIST OF FIGURES
Number Page
1 Sample analysis and report of participant's data 6
2 Control chart 7
3 Histogram of gross alpha activity in water results, 1974 . . 10
4 Histogram of gross beta activity in water results, 1974 . . 11
5 Histogram of radium-226 in water results, 1974 12
6 Histogram of tritium in water results, 1974 14
7 Standard deviation as a function of tritium concentration . 15
8 Histogram of gamma in water results, 1974 17
LIST OF TABLES
1 Summary of cross-check programs 2
2 Summary of water analysis data for gross alpha and
gross beta activity, 1974 9
3 Summary of water analysis data for radium-226, 1974 .... 13
4 Summary of water analysis data for tritium, 1974 13
5 Summary of water analysis data for gamma, 1974 16
6 Summary of laboratory performance, 1974 interlaboratory
comparison studies - water 18
iv
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INTRODUCTION
Environmental radiation measurements are made daily by Federal, State,
local, and private agencies. The data obtained from these measurements are
utilized by the U.S. Environmental Protection Agency (EPA) and other agencies
for such purposes as estimating dose, health effects, establishing standards
and guides, and conducting regulatory activities. It is therefore imperative
that the precision and accuracy of the data be assured so that policy deci-
sions concerning environmental quality are based on valid and comparable
data.
The present radiation quality assurance program of the EPA is designed
to encourage the development and implementation of quality control procedures
at all levels of sample collection, analysis, data processing, and reporting.
As an integral part of the EPA's program, the Quality Assurance Branch of the
Environmental Monitoring and Support Laboratory-Las Vegas (EMSL-LV) distri-
butes calibrated radionuclide solutions for instrument calibration and chemi-
cal yield determinations, and conducts a number of laboratory performance
studies involving the analysis of radionuclides in environmental media.
The intercomparison studies program enables participating laboratories
to maintain checks on their analyses and assists them in documenting the
validity of their data. In addition, this program enables the EPA to obtain
an overall estimate of the precision and accuracy of environmental radiation
measurements, or more precisely the precision and accuracy of laboratory
radioassay procedures for environmental samples.
Studies currently in progress involve samples of most environmental
media and include milk, air, water, soil, diet, urine, and noble gases.
Table 1 is a summary of the cross-check programs. Participants include
nuclear facilities and/or their contractors, and State, Federal, and inter-
national laboratories. The number of participants has increased steadily
during the past two years. Because of the large number of participants and
the continuing nature of the programs, sufficient data are generated to
enable periodic assessment of the quality of environmental data.
Participating laboratories perform analyses on the cross-check samples
and return their data to the Quality Assurance Branch for statistical analy-
sis. Comparisons are made between laboratories and within an individual
laboratory for accuracy and precision. A computer report and a periodically
updated performance chart are returned to each participant. This enables
each laboratory to document the precision and accuracy of its radiation
data, to identify instrumental and procedural problems, and to compare per-
formance with other laboratories.
Reported herein are the results of that portion of the quality assurance
studies which concerns the measurements of radionuclides in water samples.
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TABLE 1. SUMMARY OF CROSS-CHECK PROGRAMS*
SAMPLE
Milk
Water
Gross a, B*
Gamma
3H
239pu*
226Ra
Air
Gross a, B*
239pu*
Soil*
Diet
Urine
Gas
ANALYSIS
89Sr, 9°Sr, 131J,
I3?cs, ll*0Ba, K
Gross o, B
60Co, 106Ru, 13"Cs,
137ns. 51Cr. 65Zn
3H
239pu
226Ra
a, 3, Y
239Pu
239pu
89Sr, 90Sr, 131I,
137Cs. 140Ba> K
3H
85Kr
ACTIVITY
PER ISOTOPE
< 200 pCi/1
< 100 pCi/1
< 500 pCi/1
< 3500 pCi/1
< 10 pCi/1
< 20 pCi/1
< 200 pCi /sample
< 2 pCi /sample
< 50 pCi /sample
< 200 pCi/kg
< 3500 pCi/1
< 20 pCi/ml
QUANTITY
SUPPLIED
'o 4 1 iters
^ 4 1 i ters
^ 4 liters
^ 60 ml
^ 4 liters
^ 4 liters
3 - 2" or 4"
diam. air filters
3 - 2" or 4"
diam. air filters
^ 100 g
3 - 4-liter
samples
^ 60 ml
10 liters
PRESERVATIVE
Formalin
0.5N. HN03
0.5N. HN03
none
0.5N. HN03
0.5N_ HN03
none
none
none
Formalin
Formal in
none
DISTRIBUTION
Bimonthly
Bimonthly
Bimonthly
Bimonthly
Semiannual ly
Quarterly
Quarterly
Quarterly
H
Semiannually
Quarterly
Quarterly
Semiannual ly
TIME FOR
ANALYSIS
& REPORT
6 weeks
4 weeks
4 weeks
4 weeks
8 weeks
6 weeks
4 weeks
6 weeks
8 weeks
8 weeks
4 weeks
8 weeks
i
Laboratories are required to have the necessary licenses before receiving these samples,
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METHODS AND PROCEDURES
Water samples containing known amounts of specific radionuclides are
prepared and distributed to a number of Federal, State, and private labora-
tories. These samples are designed to test the ability of participating
laboratories to analyze water for gross alpha and gross beta activity,
radium-226, gamma-emitting isotopes, and tritium. A schedule of the water
samples distributed during 1974 is shown below.
Analysis Jan^ Feb Majr^ AJJJT May Jun Jul Aug Sep Oct Nov Dec
Gross Alpha Activity x x x x x
Gross Beta Activity x x x x x
Radium-226 x x x x
Gamma Emitters x x x x x x
Tritium x x x x x x
The quantity and activity levels of each type of sample are described in the
following paragraphs.
1. Samples for the Analysis of Gross Alpha and Gross Beta Activity
A 4-liter water sample containing known amounts of americium-241
and strontium-go-yttrium-go was sent to each participant. Five different
samples were distributed during 1974. The concentration of americium-241
varied from 50 pCi/liter (November) to 90 pCi/liter (April), while that of
strontium-go-yttrium-go varied from 24 pCi/liter (February) to 190 pCi/liter
(April).
2. Samples for the Analysis of Radium-226
A 4-liter water sample containing known amounts of radium-226 was
distributed to each participating laboratory. During 1974 four different
samples were supplied for analysis. The concentrations of radium-226 in
these samples varied from 5 pCi/liter (July and November) to 16 pCi/liter
(January).
3. Samples for Gamma-Emitting Isotopes
Four-liter water samples containing different gamma-emitting
isotopes were supplied to each participant. In this study an attempt was
made to identify instrumental or calibration problems that might exist in the
participating laboratories. Therefore, from January 1974 through October
1974 known amounts of a single radionuclide were added to the water. Each of
the five intercomparison studies conducted during this period contained a
different radionuclide, i.e., zinc-65, cobalt-60, chromium-51, ruthenium-106,
and cesium-134. The concentrations varied from 339 pCi/liter (chromium-51
-------
in May) to 481 pCi/Titer (cesium-134 in October). In December 1974, the
samples contained a mixture of cesium-134 (452 pCi/liter), cesium-137 (497
pCi/liter), and cobalt-60 (478 pCi/liter).
4. Samples for Tritium Analysis
During 1974, 60-milliliter samples containing known amounts of
tritium were supplied to participating laboratories on a bimonthly basis.
The concentrations of these samples varied from 1491 pCi/liter (August) to
3395 pCi/liter (March).
PREPARATION OF WATER SAMPLES
1. The water utilized in preparing samples for gross alpha and gross
beta activity analyses, radium-226 measurements, and for the assay of gamma-
emitting radionuclides, is a mixture of distilled water, aged for a minimum
of 30 days, tap water, and nitric acid. This mixture is prepared in large
100-gallon plastic tanks. Appropriate amounts of the three constituents are
added to the tank and stirred for 3 hours. Upon completion of the initial
mixing, aliquots are removed and counted for background determination before
the radionuclides are added. Prior to the addition of the "spike," the water
sample consists of 0.5^ nitric acid and 10 percent tap water, and contains 70
to 75 milligrams/liter of dissolved and suspended solids. Accurately measured
amounts of the desired radionuclides are added to the water and stirred con-
stantly for approximately 17 hours. The solution is then transferred to
4-liter cubitainers for distribution to participants. However, three ali-
quots are analyzed for activity and the homogeneity of the total sample
checked before the individual samples are shipped to the participating labora-
tories.
2. Deep-well water containing no more than 15 pCi/liter of tritium is
utilized in the preparation of the tritium samples. The well water is dis-
tilled and checked for the presence of chloride ions. The total water sample
is then divided. Half of the distillate is utilized in the preparation of
60-milliliter background samples, while the desired amount of the tritium is
added to the other half. The portion containing the tritium is thoroughly
mixed and sealed in 60-milliliter glass bottles for distribution. Before
shipping to participants, random samples are analyzed and the batch checked
for homogeneity.
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ANALYSIS BY PARTICIPANTS
Participating laboratories conduct three independent determinations for
each radionuclide included in the particular cross-check sample and report
the results to the Quality Assurance Branch. Control limits (sigma limits)
previously established by the Analytical Quality Control Service in Winchester,
Massachusetts, are used in analyzing the quality of the results obtained by
these laboratories. These limits are based on the purpose for which the
data are being obtained and on reasonable laboratory ability. Upon receipt
of the reports from all participating laboratories, the data are analyzed
using a computer. This analysis includes determination of the experimental
average and standard deviation (S) of the samples, the normalized range (R),
standard error, normalized deviation, experimental sigma, and the grand
average of all laboratories for each radionuclide. Examples of sample
calculations to illustrate the computations performed by the computer are
shown in the Appendix.
A report is generated containing the data reported by all participating
laboratories, listed according to identity code, along with the results of
the data analysis. Examples are shown in Figure 1. In addition, a control
chart is generated for each radionuclide included in the sample (Figure 2).
The control charts are updated each time a laboratory participates in a
cross-check study, thus giving each laboratory a continuous record of its
performance. A copy of the computer printout and a control chart for each
radionuclide are mailed to each participant approximately 4 weeks following
the report due date.
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EMSL-LV TRITIUM IN WATER CROSS-CHECK PROGRAM DECEMBER 1974
12/27/74 SAMPLE - A 3H
KNOWN VALUE = 1579 PCI/L
EXPECTED LABORATORY PRECISION (IS, 1 DETERMINATION) = 332 PCI/L
EXPERIMENTAL
LAB RESULT SIGMA
57.7
140.5
47.3
94.4
382.9
NO DATA PROVIDED
D
D
D
P
P
P
AG
AG
AG
AH
AH
AH
AI
AI
AI
1500
1400
1400
1872
1688
1596
1830
1810
1740
1626
1477
1652
2011
1713
2473
RNG ANLY
(R - SR)
.18
.49
.16
.31
1.41
AVERAGE
1433
1719
1793
1585
2066
NORMALIZED DEVIATION
(GRAND AVG) (KNOWN)
-1.5
-.0
.4
-.7
1.8
-.8
.7
1.1
-.0
2.5
EXPERIMENTAL SIGMA (ALL LABS) = 272
GRAND AVERAGE = 1719
Figure 1. Sample analysis and report of participant's data
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CO
TRITIUM IN WATER CROSS-CHECK PROGRAM
LAB-D 3H
NORMALIZED DEVIATION FROM KNOWN
3
2
1
0
-1
-2
-3
~4
1973
. 0
•' *"• «7\ • •
V v
1974
.
^ \ • *N •
^ \/ * V.
•
J FMAMJJASONDJFMAMJJASOND
NORMALIZED RANGE
R + 3
R + 2
R + 1
R + 0
1973
• • _ . . 1 • 1 1 1 .
1974
I I. .1.1 !._••
CL
WL
WL
CL
CL
WL
JFMAMJJASONDJFMAMJJASO ND
Figure 2. Control chart
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RESULTS AND DISCUSSION
1. Gross Alpha Activity
The results of the gross alpha studies are summarized in Table 2
and Figure 3. Most of the reported results are within the established con-
trol limits. The internal precision of the individual laboratories, although
not shown in this paper, appears to be generally satisfactory. However,
there is a need for improved accuracy, as indicated by the difference between
the average and known values. Moreover, in the five studies, the average of
the reported results (x) in all cases, was less than the known amounts of
activity added to the sample (y). This negative bias may be due to the loss
of a portion of the sample, resulting from adherence to the sides of the
beaker during the evaporative procedure employed in sample preparation.
The values (a/y) times 100 and (s/y) times 100 obtained from the
five studies are compared in Table 2. These values indicate that the control
limits are realistic and, with improved calibration procedures and uniform
methodology, readily attainable.
2. Gross Beta Activity
The results of the gross beta studies are illustrated in Figure 4
and summarized in Table 2. In all five of these studies the average values
reported by the participants exceeded the known values. This positive bias
may be due to the fact that commonly used procedures require that gross beta
values be corrected for gross alpha interference. Since the gross alpha
values are consistently low, as indicated above, the alpha correction factors
applied may not be large enough.
The intralaboratory precision for gross beta analysis appears to be
quite satisfactory. However, the accuracy of these measurements is unsatis-
factory. A significant number of the values reported by the participating
laboratories extend beyond the control limits, indicating that the expected
accuracy of the gross beta analytical procedure is not being attained. Com-
parison of (a/y) times 100 with the experimentally determined (s/y) times 100
further indicates that a large number of participating laboratories are not
meeting the established limits.
8
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TABLE 2. SUMMARY OF WATER ANALYSIS DATA FOR
GROSS ALPHA AND GROSS BETA ACTIVITY, 1974
u (pCi/liter)
a limit (pCi/liter)
(a/y) x 100 (%)
N
x (pCi/liter)
s (pCi/liter)
(s/y) x 100 (%)
February
51
13
25.5
28
38
19
37.3
Apri 1
95
24
25.3
27
64
28
29.5
July
ALPHA
75
19
25.3
28
59
26
34.7
September
25
6.3
25.2
30
21
8
32.0
November
50
12.6
25.2
31
41
15
30.0
BETA
y (pCi/liter)
a limit (pCi/liter)
(a/y) x 100 (%)
N
x (pCi/liter)
s (pCi/liter)
(s/y) x 100 (%)
24
5
20.8
30
33
9
37.5
190
10
5.3
30
199
39
20.5
103
5
4.9
30
112
21
20.4
77
5.0
6.5
30
80
15
19.5
51
5.0
9.8
34
57
13
25.5
-------
Freq.
10
h—I =±30
CONTROL LIMIT
FEBRUARY
\ h
125 150 175
APRIL
JULY
x 21
M 25
75 100 125 150 175
SEPTEMBER
0 ' 25 50 75 100 125 150 175
x 41 M 50
NOVEMBER
75 100 125 150 175
pCi/liter
Figure 3. Histogram of gross alpha activity in water results, 1974
10
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33
4
FEBRUARY
0 ?b 60
100
IbO I7b 700 7?b 7bO 77b 300
IO
n|
190 T 199
APRIL
0 7b bO Ib 100 i?b IbO1 rft, J ft 0 ?25 ? b ° ?7!> 30D
Freq.
10
0 2b bO 7b
T = II?
p * 103 i
JjU-
^b' lifl ' 17b V.
JULY
-h
IbO 17b 700 7?b 7bO 27b 300
p = 77 T 80
^li^
t n ' -1C. 1 , n n
SEPTEM BER
•4-
0 ?b bO 75 100 l?b IbO 17b 700 ??b 7SO 77S 300
b7
NOVEMBER
0 bO 7b
100 l?b IbO I7b 700 7?b 7bO 7 7 b 300
pCi/liter
Figure 4. Histogram of gross beta activity in water results, 1974
11
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3. Radium-226
The results of the radium-226 studies are shown in Figure 5 and
Table 3. These results indicate most of the participating laboratories are
performing satisfactory analysis. Eighty percent of the reported values are
within the established control limits. Although not shown in this report,
the internal precision of the individual laboratories appears to be satis-
factory. Comparison of (a/y) times 100 with the experimentally determined
(s/u) times 100 indicates most participating laboratories are meeting the
established limits.
JT =u= 16
JANUARY
0 5
15 20 ' 25
Freq.
20 25
MAY
JULY
0 5 10 15 20 25
,x =M= 5
NOVEMBER
1 1 1
0 ' 5 " 10 15 20 25
pCi/liter
Figure 5. Histogram of radium-226
in water results, 1974
12
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TABLE 3. SUMMARY OF WATER ANALYSIS DATA FOR RADIUM-226, 1974
y (pCi/liter)
a limit (pCi/liter)
(a/y) x 100 (%)
N
x (pCi/liter)
s (pCi/liter)
(s/y) x 100 (%)
January
16
2
' 12.5
10
16
3
18.8
May
10
2
20.0
14
11
2
20.0
July
5.1
0.8
15.7
13
5
1
19.6
November
4.9
0.7
14.3
10
5
1
20.4
4. Tritium
The results of the tritium studies are shown in Table 4 and
Figure 6. The established control limits for tritium are a function of the
concentration as shown in Figure 7- For the analyses of the six intercom-
pan" son studies, the range of these limits varies from 10.2 to 23.0 percent
of the known value at the 1 sigma control limit. Of all the water analyses
performed by the cross-check participants, the tritium results indicate that
90 percent of the laboratories are within the 3 sigma control limits. Also,
the results show no significant bias.
One reason for these results may be attributed to the fact that all
laboratories use essentially the same method of analysis. Again, the pre-
cision (not shown) for tritium analysis appears good. A comparison of (a/y)
times 100 with the experimentally determined'(s/y) times 100 further substan-
tiates the accuracy of the data reported by the participating laboratories.
TABLE 4. SUMMARY OF WATER ANALYSIS DATA FOR TRITIUM, 1974
y (pCi/ liter)
a limit (pCi/liter)
(a/y) x 100 (%)
N
x (pCi /liter)
s (pCi /liter)
(s/y) x 100 (%)
January
1755
335
19.1
38
1771
324
18.5
March
3395
346
10.2
41
3331
332
9.8
May
2673
353
13.2
40
2669
236
8.8
August
1438
331
23.0
33
1491
255
17.7
October
1975
350
17.7
37
1979
301
15.2
December
3395
356
10.5
44
3252
307
9.0
13
-------
JANUARY
1000 201)0 3000 4000
MARCH
15- .
10- .
5. .
0,
1000 2000 3000 4000
= 2669
M 2673
MAY
15-
10.
5.
0
1000 ' 2000 3000 MOOO
Freq.
x = 1438 M 1491
AUGUST
3000 4000
M = 1975 7 = 1979
OCTOBER
15-
'0.
5. .
0
4000
M 3395 DECEMBER
«" = 3331
1000 2000 3000 4000
pd/liter
Figure 6. Histogram of tritium in water results, 1974
14
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en
80
75
70
65
60
55
50
—. 45
X 40
«*-
Q
35
s£
— 30
t> 25
20
15
10
5
LIQUID SCINTILLATION
COUNTING TIME = 100 MINUTES
5 ml. ALIQUOT
5.7 cpm BACKGROUND
DIOXANE BASE COCKTAIL
= 16984 x
-9067
I 500 I 1000 I 1500 I 2000 I 2500 I 3000 1 3500 1 4000
250 I 750 I 1250 I 1750 I 2250 I 2750 I 3250 I 3750 I
x (pCi/liter)
Figure 7. Standard deviation as a function of tritium concentration
-------
5. Gamma
The results of the gamma in water studies are summarized in Table 5
and Figure 8. All cross-check samples contained single nuclides with the
exception of the December sample which contained cesium-134, cesium-137, and
cobalt-60. Ability of the participating laboratories to perform gamma analy-
ses varied markedly with individual nuclides. Of the participating labora-
tories, 77 percent were within the 3 sigma control limits for cobalt-60 while
only 50 percent were within the limits for chromium-51. Since ruthenium-106,
chromium-51, zinc-65, and cesium-137 were present in only one cross-check
sample each, and cobalt-60 and cesium-134 present in only two, no definite
conclusion with regard to laboratory performance can be made at this time.
However, results of the samples containing only one gamma-emitting radio-
nuclide would suggest a need for better instrument calibration procedures.
TABLE 5. SUMMARY OF WATER ANALYSIS DATA FOR GAMMA, 1974
u (pCi /liter)
o limit (pCi/liter)
(o/u) x 100 (%)
N
x (pCi/liter)
s (pCi/liter)
(s/u) x 100 (%)
January
65Zn
372
19
5.1
31
392
52
14.0
March
60Co
490
24
4.9
29
478
29
5.9
May
51Cr
349
17
5
30
331
53
15.2
August
106Ru
421
21
5
34
423
49
11.6
October
13"Cs
481
24
5
39
467
40
8.3
60Co
478
24
5
31
476
23
4.8
December
13"Cs
452
23
5
34
440
39
8.6
137Cs
497
25
5
32
496
41
8.3
16
-------
= ±3o
CONTROL LIMIT
Zinc-65
JANUARY
M = 481
x = 467
200 300 400 500 600
If = 478 ,M = 490
Cesium-134
OCTOBER
300 400 500 600 700
10--
5 ..
Freq.
"""fli^-—-Tl
Cobalt-60
MARCH
200 300 400 500 600
M = 339
Freq.
Cesium-134
DECEMBER
300
600 700
Chromium-51
MAY
200
0 500 600
Ruthenium -106
AUGUST
200 300 400 500 600
pCi/liter
Cesium-137
DECEMBER
Cobalt-60
DECEM BER
300 4dO 500 600 700
pCi/liter
Figure 8. Histogram of gamma in water results, 1974
-------
Table 6 is a summary of the results for the ten analyses performed on the
water cross-check samples by the participating laboratories. Using the per-
centage of laboratories reporting data within the 3 sigma control limits as
criteria, the nuclides are listed in order of the ability of the laboratories
to perform the radionuclide analysis.
TABLE 6. SUMMARY OF LABORATORY PERFORMANCE
1974 INTERLABORATORY COMPARISON STUDIES - WATER
Radionuclide % of Laboratories Within ± 3
Analysis (99.7% Control Limits)
Tritium 90
Radium-226 80
Cobalt-60 . 77
Gross Alpha 67
Ruthenium-106 63
Cesium-134 62
Cesium-137 62
Zinc-65 55
Chromium-51 50
Gross Beta 44
The conclusions drawn from these data, of necessity, have been very
general due to the limited amount of available data. The data indicate
tritium to be the least difficult (90 percent within the control limits), and
gross beta to be the most difficult (44 percent within the control limits)
for laboratories to analyze. Sufficient data must be compiled over a longer
period of time to obtain a valid idea of laboratory performance. When suf-
ficient data are compiled, such parameters as control limits, methods of
analysis, and instrument calibration must be critically assessed in deter-
mining laboratory performance and, if necessary, how improvement can best be
achieved.
18
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APPENDIX. STATISTICAL CALCULATIONS
To illustrate the computations performed by the computer, example
calculations are given using data for three actual samples analyzed at
one laboratory (Laboratory D).
The experimental data are listed and the mean, range, and the
experimental sigma are computed. These statistics provide measures of
the central tendency and dispersion of the data.
The normalized range is computed by first finding the mean range,
R, the control limit, CL, and the standard error of the range, aR.
The normalized range measures the dispersion of the data (precision)
in such a form that control charts may be used. Control charts allow
one to readily compare past analytical performance with present per-
formance. In the example, the normalized range equals 0.3 R which
falls inside the upper warning level, R + 20R. The precision of the
results is acceptable.
The normalized deviation is calculated by computing the deviation
and the standard error of the mean, a . The normalized deviation
allows one to readily measure central tendency (accuracy) through the
use of control charts. Trends in analytical accuracy can be determined
in this manner. For this example, the normalized deviation is -0.7
which falls within the upper and lower warning levels. The accuracy of
the data is acceptable.
Finally, the experimental error of all laboratories, the grand
average, and the normalized deviation from the grand average are cal-
culated in order to ascertain the performance of all the laboratories
as a group. Any bias in methodology or instrumentation may be found
from these results.
19
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EXAMPLE CALCULATIONS (Laboratory D Data)
Experimental data:
Known value = y = 3273 pCi 3H/liter urine on September 24, 1974
Expected laboratory precision = a = 357 pCi/liter
Laboratory Sample Result
D xi 3060 pCi/liter
D x2 3060 pCi/liter
D x3 3240 pCi/liter
Mean = x
N
x = ~ = ^p- = 3120 pCi/liter
ll V
where N = number of results
Range = r
r = (maximum result - minimum result)
= |3240 - 3060[ = 180 pCi/liter
20
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Experimental sigma = s
s =
(3060)* + (3060)' + (3240)* - (3060 + 3060 + 3240)'
= 103.9 pCi/liter
Normalized range = wR + xaR
Mean range = R
R = d2a where d2 = 1.693 for N = 3*
= (1.693)(357)
= 604.4 pCi/liter
Control limit = CL
CL = R + 3aR
= D^R where Di, = 2.575 for N = 3*
= (2.575)(604.4)-
= 1556 pCi/liter
Standard error of the range = aR
a R = 1/3 (R + 3aR - R)
= 1/3 (D4R - R)
= 1/3 (1556 - 604.4)
= 317.2 pCi/liter
* Rosenstein, M., and A. S. Goldin, Statistieal Techniques for Quality
Control of Environmental Radioassay, AQCS Report Stat-1, U.S. Depart-
ment of Health, Education and Welfare, PHS, Nov 1964
21
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wR + xaR = 1R + xaR
= 1R +
r - wR
for r > R
wR + xaD = wR + oov
JR
= wR
180
n
K
for r ^ R
since 180 < 604.4
= 0.30 R
Normalized deviation of the mean from the known value = ND
Deviation of mean from the known value = D
D = x - u
= 3120 - 3273
= - 153 pCi/liter
Standard error of the mean = a
..... °* m Jg
_ 357
m
= 206.1 pCi/liter
ND = a
- 153
" 206TT
= - 0.7
22
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Experimental sigma (all laboratories) =
st
N \2
Z xi/
162639133 -
14
= 149 pCi/liter
Grand average = GA
N
N
- 49345
= 3290 pCi /liter
Normalized deviation from the grand average = ND1
Deviation of the mean from the grand average = D1
D1 = x - GA
= 3120 - 3290
= - 170 pCi /liter
ND1 = £-
am
- - 170
" zorn:
= - 0.8
23
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA-600/4-76-017
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
THE STATUS AND QUALITY'OF RADIATION MEASUREMENTS
OF WATER
5. REPORT DATE
April 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
A. N. Jarvis, R. F. Smiecinski, D. G. Easterly
9. PERFORMING ORG \NIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
1HD621
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
Interim, 1974
14. SPONSORING AGENCY CODE
EPA-ORD-Office of Monitoring
and Technical Support
15. SUPPLEMENTARY NOTES
16. ABSTRACT
As part of the radiation quality assurance program conducted by the U.S.
Environmental Protection Agency, calibrated radionuclide solutions are distributed
to participating laboratories for instrument calibration and yield determinations.
Laboratory performance studies involving the analysis of radionuclides in environ-
mental media are also conducted.
A summary is given of the results of the water cross-check program for 1974.
Examination of these results reveals that gross beta is the most difficult (44
percent within the control limits) and tritium is the least difficult (90 percent
within the control limits) for the laboratories to analyze. These results indicate
the need for improvement in analytical procedures for the radionuclide studies.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
radiation chemistry
quality assurance
quality control
water analysis
isotopes
radium-226
tri ti urn
chromium-51
cobalt-60
zinc-65
ruthenium-106
cesium-134
cesium-137
laboratory performance
intercomparison studies
cross-check
gross alpha
gross beta
07E
12B
14D
18B,D,H
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
28
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
ftGPO 691- 219-1976
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