United States          Office of            EPA 520/5-83-020
               Environmental Protection     Radiation Programs       September 1983
               Agency            Washington, DC 20460



               Radiation
c/EPA
               Evaluation of
               Track-Etch Detectors

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                                Disclaimer

     Track-EtchVx is a registered  trade  name  for  nuclear track detectors
made by Terradex Corporation,  Walnut  Creek, California.  Evaluation of
this product by EPA does not constitute  its endorsement by EPA.
Throughout the paper any reference to "nuclear track detectors" are those
manufactured by Terradex.

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   Evaluation of Track-Etch Detectors
              E.  0.  Savage
Eastern Environmental  Radiation  Facility
             P.  0.  Box 3009
       Montgomery,  Alabama  36193
              May 26,  1983
                  EPA
  U.S. Environmental  Protection  Agency
      Office of Radiation Programs
           Waterside Mall East
           401 M Street,  S.W.
         Washington, D.C.  20460

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Abstract	ii
List of Tables	iii
List of Figures	iii
I.    Introduction
II.   Study Objectives 	    3
III.  Methodology  	    5
IV.   Results	15
V.    Conclusions	23
References	25

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                                 Abstract

     A study was conducted to evaluate the precision  and  accuracy of
             passive radon detectors manufactured  by  the  Terradex
Corporation.  Four configurations of these detectors  were exposed to known
radon concentrations in the Eastern Environmental  Radiation  Facility radon
chamber under varying exposure regimines and sent  to  Terradex  for
processing and readout.

     Data reported by Terradex and our own exposure concentrations  were
used to calculate calibration numbers for each configuration which  were
then compared to calibration numbers used by Terradex.

     Results of our  study  indicate that groups of detectors exposed
together and processed together demonstrate similarity in response.
Groups of detectors  exposed  and processed at different times,  however,  did
not  always  agree with each other nor with published Terradex calibration
numbers.
                                     ii

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                              List of  Tables
Table 1.  Number of Detectors  Exposed	 14


Table 2.  Actual  Delivered Exposures	 14


Table 3.  Summary of Calibration  Factors	 16


Table 4.  Average Calibration  Factors  Compared to


          Terradex Reported	 17
                             List of Figures
                                                     n
Figure 1.   Four Configurations  of  Terradex Track-Etch   Detectors	  6


Figure 2.   The EERF  Radon  Calibration Facility	  8


Figure 3.   Detectors Deployed in the Exposure Chamber	 11


Figure 4.   Response  of Filter Cup  Detector, Batch 8	 19


Figure 5.   Response  of Filter Cup  Detector, Batch 10	 20


Figure 6.   Response  of Open  Cup Detector, Batch 8	 21


Figure 7.   Response  of Open  Cup Detector, Batch 10	 22
o
  Registered tradename.
                                   iii

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                               Introduction

     For the past several  years the U.S.  Environmental  Protection Agency's
Office of Radiation Programs (ORP)  has been involved in several  studies
designed to assess ambient and indoor concentrations of radon and radon
daughter products.  The data gathered in  these studies  are being used in
turn to help evaluate the health impact of population exposure to radon
and its decay products and to determine the efficiency  of remedial  and
preventative techniques.
     Radon daughter measurements are relatively  difficult due to several
contributing factors:  radon itself is a  fairly  unreactive noble gas  that
decays into particles having short  half-lives  and  a  great affinity  for
respirable airborne dust (condensation nuclei).  Much scientific attention
has been directed of late toward characterizing  the  relationship between
radon and its decay products and developing techniques  for sampling and
measuring these quantities accurately under dynamic  conditions.   Several
measurement techniques are now commonly used to  measure both  radon  and
daughter product concentrations with a fair degree of precision  and
accuracy.  Radon is commonly sampled in evacuated  scintillation  cells  and
subsequently counted on photomultiplier tubes  according to generally
accepted procedures (Lu57, Ge76).   The minimum detectable  levels generally
achievable by this method  are about 0.1 pCi/liter.   Other investigators
draw air samples into glass flasks  and metal containers and determine
radon concentrations by a  pulse ionization  technique  (Ha72).  This
procedure usually results  in a lower detection limit  of 0.05  pCi/1.

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Variations on these measurement techniques have been incorporated  by
several  equipment manufacturers into commercial devices  with integrating
flow-through characteristies and automatic sampling features.   Radon
daughter concentrations and subsequent WL determinations can be
accomplished by drawing air samples through a filter and quickly counting
the filter alpha activity.   By using the techniques and  assumptions of
several  investigators (Ku56, Th72, and Ha69), and applying alpha
spectroscopy or gross alpha counting, sensitivities of .0005 WL. are
possible.  Long-term integrated samples in the field are accomplished with
Radon Progeny Integrated Sampling Units (RPISU's) which  employ
thermoluminescent detectors to measure alpha activity trapped on filter
membranes(Sc74).  Automatic sampling and measurement devices for Working
Level determination have been developed by Argonne National Laboratory
(ANL78) and commercially by several companies.  These are commonly known
as Instant Working Level Monitors (IWLM).
      In most cases, the procedures and equipment necessary to accomplish
all  of the aforementioned measurements are cumbersome, expensive (or
both), generate heat and/or noise and  require  electrical power in  the
field.   In addition, the techniques  do not lend  themselves well to large
scale screening measurements  or  to extremely  long  (months or more)
measurement  time periods.
      It  is for these logistical  and  economic  considerations that
 inexpensive  and passive radon detectors  are  so attractive.  The ORP has
experience with two  passive systems  at  the present  time.  The first is
 known as the Passive Environmental  Radon  Monitor (PERM) which is based on
 a design by  George (Ge77).   This device  uses  a battery  to  impose a voltage
 potential  across a metal  funnel  and  a  center electrode  bearing  a
 thermoluminescent dosimeter chip (TLO).   The  alpha-emitting radon

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daughter products exist as free positive ions which are attracted to and
subsequently expose the TLD.   The second type of passive detector which we
have used is Terradex's Track-EtcfV-'Detector.  This detector consists of
a material in which tracks are formed on bombardment by a alpha particle.
When suitably processed and "developed"  the tracks become visible,  are
counted microscopically, and are related to radon concentrations via an
empirically derived calibration factor having units of  tracks/square
millimeter per pCi/liter-day.
                             Study Objectives

The objective of this study was to assess  the  accuracy  and  precision  of
the detectors as environmental  radon monitors  under several  controlled
exposure conditions.   Field testing nuclear track  detectors  is  an
objective of a much larger environmental  study currently  in  progress  at
Butte, Montana.  Existing Terradex Track-Etch^ data were  statistically
analyzed and the results formed the basis  for  designing a study to address
the following issues:

     1.   Reliability;  the extent to which  different detectors from the
         same production lot yield similar results  when exposed together.
     2.   Lot-to-lot variability;  differences in detector  response between
         2 different  production lots.
     3.   Linearity  of  response;  consistency of detector response over a
         range of total  exposures.

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     Our study evaluates detector response characteristics  by  exposure  to
known concentrations of radon and comparison of resultant calibration
factors to published values.  Terradex calibration factors  were  derived
from exposure data sets that exhibited considerable variability.   The
statistical analysis of the results of this study consist of estimations
rather than hypothesis testing.

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                                Methodology

Detectors

     The detectors used were standard nuclear track detectors purchased
from Terradex in four configurations:  the filter cup,  membrane cup,  open
cup and bare badge (see Fig. 1).  The detectors are supplied by the
manufacturer in the open cup and bare card configuration.   The customer
then assembles the required paper filter or membrane filter configuration
with provided snap ring and filter material s.
     The detectors are provided in differing configurations to satisfy
varying sampling requirements or environmental  conditions.   The open  cup
is a plastic cup with the 0.8 x 2.5 x 0.2 cm plastic nuclear track
detector fastened to the inside bottom with two strips  of  tape.  Because
it is open to the atmosphere, the open configuration detector responds  to
both radon and plated out radon daughter alpha  activity.   The manufacturer
suggests that plate-out characteristics of the  sampled  environment  may  be
derived from this type of detector.
     The membrane cup is fitted with a clear, semi-permeable  plastic
membrane that retards the diffusion rate of gases  through  it.   By virtue
of differences in radiological  half-lives,  these membranes  preferentially
discriminate against thoron and are used where  thoron interference  might
pose problems with radon measurements.
     The filter cup is covered  with a micropore paper filter  which,
according  to the manufacturer,  allows gaseous radon  to  enter  the cup  but
blocks the passage of radon daughters.   This configuration  is  preferred
where radon is to be measured alone and thoron  is  not significant.

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                       Figure 1
552756
.
                552741!
                   n
552754
                                                  n
       Four Configurations of nuclear track detectors

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     The bare badge configuration is simply the detector itself mounted on
a 6.5 cm square card.  This configuration is sensitive to radon and radon
daughter products, but only responds to plate-out on the detector surface
as compared to the open cup which responds to radioactivity on the walls
of the cup as well.
     The cup detectors are supplied by the manufacturer nested in
aluminized plastic sleeves along with filter material, snap-ring filter
retainers, data forms, etc.  The bare badges are shipped individually
packaged in glassine envelopes.  After exposure, the detectors are
returned to the manufacturer where they are processed and read.  Exposure
data is then returned to the customer.

Radon Exposure Chamber

     The EERF radon chamber was constructed on  site  of 1/2-inch plywood
supported by an aluminum frame (Fig.  2).   The overall dimensions of  the
chamber are 1.2 x 1.2 x 2.4 meters.   A door allows placement and removal
of measuring instruments.  A passbox  allows loading  of small  instruments,
detectors, and filters without disturbing the environment in the chamber.
A rubber glove port allows manipulation of devices in the chamber, and
twelve sampling ports with flow rate  meters allow  direct  air sampling from
inside the chamber.
     The EERF chamber is a continuous flow design.   The  radon-222  source
used in the chamber consists of selecting one of three gas-washing bottles
containing 25 uCi, lOOnCi  and  400uCi  respectively, of radium-226  in
solution.   The appropriate source is  selected for  the chamber
concentration desired.   Each ud*  of radium-226 generates  approximately  126
pCi  of radon-222 per minute.   The radon is harvested from the  radium

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          Figure 2
EERF Radon Calibration Facility

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solution by air bubbled through the solution at about 1 liter per minute.
The radon enriched air flows through traps and filters to remove any
inadvertent particulate radium carry-over, and then into a 20-liter aging
bottle which allows 20 minutes of radon daughter in-growth time before
release into the chamber.   Final  chamber concentrations of radon are
maintained by dilution with room air,  which is normally controlled between
50 and 200 liters per minute.   Condensation nuclei  are added to the
dilution air supply by a voltage-controlled nichrome heating wire.   An
automatic air humidifier keeps relative humidity at approximately 80
percent.  Diffuser panels  inside each  end of the chamber accomplish
homogeneity of radon concentration in  the chamber.   Having passed through
the chamber, the radon exhausts through a wall  into a large  empty room
which serves as a buffer against turbulence.   From  this room it is
exhausted to the outside by a  fan.

Exposure Measurements

     Concentrations of radon-222  in the chamber were determined  by
twice-daily grab samples in scintillation cells calibrated with  known
quantities of radium-226.   Radon  was also monitored continuously  with
calibrated flow-through radon  detectors with integrated count totals
printed out hourly.
     Working levels were determined by  twice-daily  grab samples of
filtered air with concentrations  calculated according  to  a Modified
Tsivoglou technique (Th70)  or  an  alpha  spectroscopy  technique (Ma69).  The
alpha counter used is calibrated  with a reference source  of  known
activity.  In addition,  the EERF  hosted an intelaboratory radon/daughter
measurement conference in  September, 1981,  in  which  representatives  from

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the Bureau of Mines,  Environmental  Measurements  Laboratory,  Oak  Ridge
National Laboratories, Argonne National  Laboratory,  Mound Laboratory and
Lawrence Berkeley Laboratory participated in intercal ibration
measurements.  All EERF radon exposure data have been corrected  to the
calibrated values obtained during the exercise.   These corrected radon
values, then, are the "true" radon values used in this study against which
the values reported by Terradex are compared.  Stability and statistical
characteristics of our radon data are presented in the Results section  of
this report.
     Condensation nuclei concentrations were monitored with an Environment
One Model Rich-100 Condensation Nuclei Counter and the data recorded on a
strip chart  recorder.
     Temperature  and  humidity were measured with standard gauges mounted
inside  the chamber, with values  recorded manually each day.

Exposures Protocol

     For  each  exposure, the desired  concentration of  radon was selected
and allowed  to stabilize  in the  chamber  as  determined by a flow-through
detector  and scintillation  cell  measurements.  Detectors for the
experiment  were then  introduced  into the chamber through the passbox and
 suspended on a three-dimensional  string  matrix  such that approximately  .3
meters of free space  surrounded  each detector (Fig. 3).  The detectors
 were left in the chamber  long enough to  accumulate the desired exposure
 and were then removed, packaged  according  to the manufacturer's
 instructions,  and shipped to the manufacturer for processing.
                                     10

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              Figure 3

Detectors Deployed  in Exposure Chamber
                   I

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     The exposure protocol  required two series of runs,  each series
consisting of one run for 10 days at 100 pCi/liter,  one  for 20 days  at  50
pCi/liter, and one for 40 days at 25 pCi/liter, thus delivering the  same
total exposure in three different exposure patterns.  The entire series of
runs for all three exposures was repeated and constituted the second
series of runs.  In addition, linearity of detector response was
determined by sequentially removing selected detectors from the exposure
chamber during one of the exposure runs.
     Once radon concentration in the chamber had stabilized and been
determined, exposure duration was altered to deliver the cumulative
exposure  of as near to  1000  pCi/1-day as possible.  This was designed to
test the  accuracy with which the exposure was  delivered and measured, an
essential component of  a calibration study.  During each run, the chamber
contained various numbers of detectors  in each of the four configurations,
including for each configuration at least one  detector from two production
batches,  Batch 8  and Batch  10.
     At  the  time  the study was  designed, two assumptions were made that
 had to be changed midway through the study:  detector reliability was good
 and lot-to-lot variability was  small.   Both of these assumptions tended to
 keep the number  of  required  data points quite  small in the  initial study
 design.   After the  initiation of the first  series of  runs,  the
 manufacturer announced an  approximate  30 percent difference  in  detector
 response between Batch 8 and Batch 10.   In  addition,  preliminary analysis
 of the data from the first series  of  runs  indicated greater than expected
 variability.   For these reasons it was deemed  prudent to expand the  data
 base during the  second series of runs, and,  consequently,  more  detectors
                                     12

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of each kind were exposed.   Table 1 summarizes the numbers of detectors of


each type used in each series of exposure runs,  Table 2 summarizes the


exposures achieved for the  various stages of this study.


     The final design-related item of note involved the selection of


detector area to be read.   The manufacturer offers three  standard

              22          2
choices:  1 mm , 5 mm ,  or  15 mm , with respectively increasing


sensitivity due to statistical  resolution.   It was expected  that


difficulty in maintaining exposure levels would  dominate  the overall

                                                                   2
error,  and for that reason  the sensitivity associated with the  5 mm

                                                                       2
service was judged adequate.   All  detectors used in this  study  had 5  mm


read.
                                   13

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                        Table 1.  Number of Detectors Used
A.   1st Series
                      Lot 1 (Batch 8)
                                             Lot 2 (Batch  10)
Configuration(a)
      M
 0
Nominal Exposure
Length (days)

40                   1111
20                   1111
10                   1111
Configuration a)
                        Nominal Exposure
                        Length (days)

                        40
                        20
                        10
MOB
                                  1111
                                  1111
                                  1111
B.  2nd Series
                            Lot 1 (Batch 8)
                                            Lot 2 (Batch 10)
Configuration(a)
      M
0
 Nominal Exposure
 Length  (days)

 40                  4442
 20                  4442
 10                  4442
Configuration (a)
M
                        Nominal Exposure
                        Length (days)

                        40
                        20
                        10
                                   4444
                                   4444
                                   4444
         F   =  Filter cup.
         M   =  Membrane cup,
         0   =  Open cup.
         B   =  Bare Card.
                        Table 2.   Actual Delivered Exposures
   Purpose
Rn Concentration (pCi/1)     Duration  (days)
                                     Total  Exposure
                                     (pCi/liter-day)
Calibration
Calibration
Calibration
Calibration
Calibration
Calibration
Linearity
Linearity
Quality Control
110.00
98.84
55.12
50.91
26.90
26.09
110.70
109.80
110.00
9
10
18
20
38
38
3
6
9
990.0
988.4
992.2
1018.2
1022. 2
991.4
332.1
658.8
990.0
                                          14

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                                  Results

Chamber Stability
     Exposure characteristics throughout the study were excellent.
Flow-through samples with integrated hourly count totals in  conjunction
with twice-daily scintillation cell  grab samples  were  used to  verify
concentrations in the chamber.  Average concentrations and one standard
deviation indicated less than five percent variation in radon
concentration over all  exposure runs.   Details of quality assurance
procedures for the EERF radon chamber are  available separately (EPA82).
Radon concentration data produced by the EERF flow-through detector  radon
concentrations were used with track densities reported by the  manufacturer
to calculate calibration factors.

Calibration Factors
     A summary of all  calibration  factors  determined during  the study are
shown in Table 3.  For purposes of clarity it is  noted again here that
each series is composed of three runs  each (10, 20, and 40 day
exposures).  The average calibration factor for all detectors  of each type
and batch in each series is compared to the manufacturer's reported
calibration factors in Table 4.
     The data in Table 4 indicate  that the variation in  calibration
factors for the first series of runs ranged from  a  percent relative
standard deviation of 6.9 percent  (bare configuration,  Batch 10) to 31.2
percent (membrane configuration, Batch 10).
     Variation in the second series  of runs was also higher, ranging from
12.2 percent "relative standard deviation (bare  configuration, Batch 10) to
34.1 percent relative standard deviation for the  open  configuration,  Batch
                                    15

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                        Table 3.  Summary of Calibration Factors (Tracks/mm  per pCi /I iter-day
Nomi nal
Exposure
Length
Configuration/
Batch
F8
F10
B8
BIO
M8
M10
08
010

Series
.0295
.0283
.0728
.0956
.0121
.0135
.0610
.0656
10 Days


Series
.0207
.0584
.0490
.0734
.0114
.0195
.0324
.1046
+ .
+" .
+ .
T .
+_ .
T .
+" .
0025%
0198%
0014%
0071%
0011%
0032%
0022%
0425%
20
1st
Series
.0257
.0340
.0496
.0832
.0116
.0173
.0368
.0573
Days
2nd
Series
.0201 + .
.0547 + .
.0417 + .
.0686 + .
.0135 + .
.0225 + .
.0349 + .
.1019 + .


0009%
0104%
0036%
0059%
0011%
0035%
0025%
0227%

1st
Series
.0321
.0441
.0576
.0882
.0153
.0249
.0634
.0699
40 Days


2nd
Series
.0193
.0438
.0582
.0821
.0133
.0276
.0349
.1032
+
T
T
T
T
T
7
.0015%
.0049%
.0009%
.0037%
.0021%
.0054%
.0041%
.0329%
Numbers in the 1st series are single data points and appear without error terms.
Calibration factors are average of all  data points in each category.   Error term  equals  one  standard  deviation.

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                 Table 4.  Manufacturer Calibration Factors
1st Series
2nd Series
(N=3)
F8(b)
F10
B8
M10
08
0
B8
BIO
.0291 +
.0355 T
.0130 +
.0186 T
.0537 +
.0643 +
.0600 +
.0890 +
.0032
.0080
.0020
.0058
.0147
.0064
.0118
.0062
(11%)
(22.5%)
(15.4%)
(31.2%)
(27.3%)
(9.9%)
(19.6%)
(6.9%)
.0200
.0523
.0127
.0232
.0341
.1032
.0496
.0747
(N=12)
+
T
T
T
T
+"
T
±
.0019
.0157
.0019
.0058
.0034
.0352
.0090
.0091
(9
(30
(14
(25
(9
(34
(18
(12
Reported
Manufacturer
.7%)
.0%)
.9%)
.0%)
•9%)
.1%)
•1%)
•2%)
.0372
.0484
.0223
.0290
.0562
.0731
.0891
.1158
+
T
T
T
T
T
T
+"
by
(A181)
16%
16%
26%
26%
22%
22%
20%
20%
(a' Midway t.hrouah t.hp st.urlv. the manufarturpr reDorted an aoDroximate
       30  percent  increase in Batch 10 sensitivity which is reflected in
       the Batch 10 calibration factors.

(b)     p = filter  configuration
       B = Bare configuration
       M = Membrane configuration
       0 = Open cup configuration

       Error terms = one standard deviation.
                                   17

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10.   Of the 16 average calibration factors determined,  vary  significantly
from the manufacturer's reported values,  the variability distributed
mostly among configurations and batches,  in the second  series.
     In comparing the first series averages with the second  series
averages, the first series was higher (range 2 percent  to 57 percent)  in 5
of 8 cases.  The first series averages were lower (range 20  percent to 38
percent) in the  remaining 3 cases.

Lot-to-Lot Variability
     Batch 10 detectors showed an increased sensitivity in all  cases,  thus
confirming the manufacturer's report.  In most cases, however,  the degree
of  sensitivity increase was substantially greater than  the reported 30
percent.

Linearity
      Linearity of detector  response over the  range of total  exposure was
seen  for both the filter and open configurations.  Figs. 4-7 show this
linearity  and the linear regression analysis  of each batch (lot) and
configuration.   Filter detectors  showed a slope of .03955 (coefficient of
correspondence = .99805) and  .03055 (coefficient of correspondence =
 .9350)  for Batch 8  and Batch  10,  respectively.  The open configuration
detectors  showed slopes of  .06309 (coefficient of correspondence = .98110)
and .07200 (coefficient of  correspondence =  .98890) for Batch 8 and 10,
 respectively.  The  error bars on  the  data points represent one standard
deviation.   Each data point is  the average  of 2 detectors.  The linearity
portion of the  study  was done with a  minimum  of data points but was
 designed to  reveal  any anomolous  non-linearities which could have affected
other areas  of  the  study.   No  such anonalies  were found.
                                     18

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          50
          40
Tracks/mm2
          30
          20
          10
                              Figure 4
                 100        300        500        700        900
                                        pCi/l-Days
             Linearity Plot for Batch  8 Filter Detectors
                                  19

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          50
          40
Tracks/mm2
          30
          20
          10
                                Figure 5
                 100        300        500        700        900
                                        pCi/l-Days
             Linearity Plot for Batch 10 Filter Detectors
                                  20

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                               Figure 6
Tracks/mm3
          10
                 100        300        500        700        900
                                        pCi/l-Days
              Linearity  Plot for Batch 8 Open Detectors
                                  21

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                             Figure 7
          80
          70
          60
          50
          40
Tracks/mm2
          30
          20
          10
                  100         300         500         700         900





                                         pCi/l-Oays




            Linearity Plot for Batch 10 Open Dosimeters
                                 22

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Quality Control

     Twenty Batch 8 filter configuration  detectors exposed together during
the first run were divided into  two  groups  (5 and 15), each submitted for
processing and read out at a  different  time.  Approximately six months
separated the processing of the  two  groups.
     The calibration factor for  the  first group was  .0359 +_ .0016 and the
calibration factor for the second  group was  .0224+^  .0057, a decrease of
about 38 percent.

                               Conclusions

     The results  of this evaluation  tend to  support  the conclusion that
detectors exposed together and processed together will yield good
statistics.  The  calibration  factors seen in Table 3 indicate that there
is no apparent affect of length  of exposure on detector response.  If not
processed together, the detectors exhibit a  rather large and randomly
distributed variability as shown in Table 4.  If coupled with a precise
determination of  appropriate  calibration factors (in one's own calibration
chamber), the detectors should prove useful over the range of exposures
used in this study.   Also,  our data indicate linearity of detector
response.
     It was recognized at the beginning of the study that the detectors
respond not only  to Rn-222 but also to  radon daughter product alpha
particles (Po-214,  Po-218).   The bare detector configuration and probably
to some extent the open cup configuration would be expected to exhibit
some variability  in response  due to daughter product plate-out on detector
                                   23

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surfaces.   Working level  equilibrium conditions  during  exposures would
then impact the response  of those detectors.   No attempt  was made  to
rigidly control the equilibrium conditions during exposure  runs but  random
grab samples throughout the study consistently indicated  an approximate  50
percent equilibrium condition.
     The unpredictable variations exhibited between exposure  runs,
however, underscore the necessity for using the detectors with stringent
calibration and quality control techniques.
     The differences in lot-to-lot sensitivity are significant and must  be
considered when use of the detectors may involve more than one production
lot.
     Differences  in many factors - chamber equilibrium, exposure  levels
used, cup manufacture, detector processing and  reading - could conceivably
explain differences between first and second series of runs.   It  is
perhaps worth  noting that  the  results in this study are similar to results
previously  reported by the manufacturer in that  results within a  run were
very consistent,  but  results between runs were  not.  Further study should
be  designed to delineate the source of variability in these detectors,
particularly at lower  exposures  levels.
                                     24

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                                REFERENCES

AT81     Alter, H. Ward and Fleischer,  Robert I.,  1981,  Passive
         Integrating Radon Monitor for Environmental  Monitoring, Health
         Physics, 40 693 1981.

ANL74    Argonne National  Laboratory,  1974, An Instant Working Level Meter
         with Automatic Individual  Radon-Daughter  Readout.  Final Report
         for U.S. Bureau of Mines  Contract No.  H0122106, August 1974.

EPA82    Environmental  Protection  Agency,  1982, Quality Assurance Project
         Plan for the EERF Radon Calibration  Facility, Montgomery, Alabama.

Ge76     George, A.C.,  1976,  Scintillation Flasks  for the Determination of
         Low Level Concentrations  of Radon.   Proceedings of Ninth Midyear
         Health Physics Symposium,  Denver, Colorado, February 1976.

Ge77     George, A.C.  and  Breslin,  A.J., 1977. Measuring Radiation in and
         Around Uranium Mills.   Workshop of Methods for Measuring
         Radiation in and  Around Uranium Mills, ed. E.O.  Harward, Atomic
         Industrial  Forum,  Inc., Program Report, Vol. 3 1977.

Ha72     Harley, J.H.,  ed., EML  Procedures Manual, U.S.  Department of
         Energy Report  HASL-300, updated annually 1972.

Ha69     Harley, N.H. and  Pasternack/B.S., 1969, The Rapid Estimation of
         Radon Daughter Working  Levels When Daughter Equilibrium is
         Unknown.   Health  Physics,  17, 109 1969.

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                           REFERENCES-Continued

Ku56     Kusnetz, H.L.,  1956,  Radon Daughters  in  Mine Atmospheres - A
         Field Method for Determining  Concentrations.  Am.  Ind. Hyg.
         Assoc. J.,  _17,  85 1956.

Lu57     Lucas, H.F., 1957, Improved Low-Level Alpha Scintillation Counter
         for Radon.   Review Sci.  Instrum.,  28, 680  1957.

Ma69     Martz, D.E., Ho-lleman, D.F.,  McCurdy, D.E., and  Schiager, K.J.,
         1969, Analysis of Atmospheric Concentrations of  RaA,  RaB and RaC
         by Alpha Spectroscopy.  Health Physics,  17, 131  1969.

Sc74     Schiager, K.J., 1974, Integrating Radon  Progeny  Air Sampler.  Am.
         Ind.  Hyg. Assoc. J., 35, 165 1974.

Th70     Thomas, J.W., 1970, Modification of the  Tsivoglou Method for
         Radon Daughters in Air.  Health Physics, 18,  113 1970.

Th72     Thomas, J.W., 1972, Measurement of Radon Daughters in Air.
         Health  Physics, 23, 783 1972.
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