ITR-17
SOUTHWESTERN RADIOLOGICAL HEALTH LABORATORY
INTRALABORATORY TECHNICAL REPORT
TLD BACKGROUND STUDY AT NTS HER FACILITIES
by
Walter R. Payne
Richard L. Douglas
I. SUMMARY
The mean background measured by TLD's was .37 ± .03 * mR/day for
Well 3 and the Area 15 dairy barn, and .52 ± ,03 mR/day at
Building 2105. There was a significant 997. difference in back-
ground levels between the farm soil and undisturbed soil at Area
15, The background for the farm soil was .51 ± .05 mR/day and
for the undisturbed soil .81 ± .06 mR/day,
II. INTRODUCTION
Thermoluminescent Dosimeters (TLD) which were used as personnel
monitoring devices during Projects SJEP, MICE and Cabriolet,,
indicated that there were whole-body exposures of persons who
had not been exposed to any known source of radiation, These
findings suggested the existence of high background levels in
certain areas of the Nevada Test Site (NTS), Investigations be-
came warranted, therefore, to localise and measure the magnitude
of theee background levels to determine whether personnel exposures,
as measured with TLD'o, ar© exposures related to experimental
studies or are the normal background levels in the areas under
study,
Since Area IS woo contaminated with Sedan fallout, investigations
wer@ Initiated in that osea, Also, excessive cultivation end
irrigation presumably increased movement of the fallout material
* Mean value ± one otandarct deviation uaed throughout this report,
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into the farm soil and lowered its exposure rate. Investigations
were therefore concurrently conducted to determine the difference,
if any, between the farm soil and undisturbed soil in that area.
A, The objectives of this study were:
1. To establish the background radiation levels at Building
2105, Area 15, and Well 3, using TLD's.
2. To determine whether a fluctuation with time occurs in
the background levels.
3, To determine the difference in background between the
farm soil and undisturbed soil at Area 15.
III. PROCEDURE
Two sets of TLD's were placed, three to each set, at each of the
following locations:
1. Office in Building 2105.
2. Dairy barn radio room at Area 15.
3. Main room in barn at Well 3,
4. At Lateral #6 in the middle of the irrigated field, Area
15.
5. Undisturbed soil 175 yards east of the end of Lateral #6.
At locations 4 and 5 above, the sets of TLD's were taped to a
stake at a height of three feet above ground. Both sets were
placed at each location at the same time. One set was collected
after six days and the other after 13 days exposure. All TLD's
were transported between SWRHL and NTS in lead-lined containers
to minimize exposure during those periods. The exposure was
calculated in mR/day for each TLD within the two sets using the
equation:
CF ~ 7 T
Net exposure (mR/day) = -°-
Tl
where: C = Gross Chart Reading (mR)
F = Individual calibration factor for each TLD
T = Total elapsed Lime for dedosing to readout
of TLU (days)
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T^ a Time during which TLD was exposed In field (days)
,7 = A correction factor to correct for the internal
background (mR/day) due to ^K activity within
the TLD1a.
The data, as presented in Table 1, were analyzed using the analysis
of variance techniques for the two-factor factorial and completely
randomized designs. ANOVA data are listed in Tables 2 and 3.
The data from the first set of TLD's exposed at Well 3 and Area 15
were combined in calculating the average background for these
locations. This was possible as the analysis of variance indicated
no significant difference, 99% confidence level, between these
locations. Only the first set of TLD data was used to calculate
the background because 6 days is more representative of the time
that personnel wear TLD's.
IV. RESULTS AND DISCUSSION
There was no significant difference in background between Well 3
and Area 15; however, there was a significant difference, 99%
confidence level, between these two and Building 2105, See Table 1,
A significant difference, 99% confidence level, was found between
the Area 15 farm soil and the Area 15 undisturbed soil. This 10
not unexpected since it was known that the tillage and frequent
watering of the farm soil would increase leaching of the Sedan
fission products.
A significant difference, 99% confidence level, in the background
exposure rate was found over time for all facilities by analyzing
the first set of data versus the second set at each location. The
average rate for the first six days at each facility ranged from
15.6% to 19.3% higher than those for the entire 13-day period.
It is assumed that this variation is due partially to an Inherent
characteristic of CaF2;Mn TLD's. Reports show that a known exposure
on TLD's will fade with time.
1 Horn, William. 1966. Evaluatien of the EG&B Thermolumlnescent
Dosimetry System. SWRHL Intralab, Teeh. Report ITR-10.
3
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The average rate of fading reported was 5.4% for 30 days, most pf
the fading apparently occurring within the first five or six days
and leveling off thereafter. The fading cannot account for the
entire difference between the sets, however, a definite statement
cannot be made concerning the fluctuation in background since
investigation of this phenomenon is outside the scope of this study.
Such investigation will be initiated promptly should future require-
ments for this detailed data become evident.
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Table I. Data Summary
TLD No. Exj
and
Location
Well 3
831
832
833
834
835
836
Barn Area 15
837
838
839 ^
840
841
842
Irrigated Field
843
844
845
846
847
848
Undisturbed Soil
849
850
851
852
853
854
Building 2105
855
8.56
857
858
859
860
sosure Time
(days)
6
6
6
13
13
13
6
6
6
13
13
13
6
6
6
13
13
13
6
6
6
13
13
13
6
6
6
13
13
13
Corrected Chart
Reading (mR)
(CF)
7.21
6.86
7.35
13.76
14.21
13.50
7.00
7.36
7.00
14.01
14.30
13.72
8.40
8.01
8.16
16.32
15.50
15.76
9.70
9.90
10.08
19.84
19.06
21.01
7.92
7.92
8.24
15.45
15.54
15.46
Net
Exposure (mR)
(CF - .7T)
2.31
1.96
2.45
3.96
4.41
3.70
2.10
2.46
2.10
4.21
4.50
3.92
3.50
3.11
3.26
6.52
5.69
5.95
4.80
5.00
5.18
10.04
9.25
11.21
3.02
3.02
3.34
5.65
5.75
5.65
Average Exposure Mean ± Stand. Mean ± Stand,
(mR/day) Dev. for set Dev. both sets
(CF - .7T) (mR/day) (mR/day)
Tl
.39
.33 .37 ± .04
.41 ..
.30
.34 .31 ± .03
.28
.35
.41 .37 ± .03
i_5 -*s -i- nt
.32
.35 .32 ± .02
.31
.58
.52 .55 ± .03
__* ___ 51 , OS
.50
.44 .47 ± .03
.46
.80
.83 .83 ± .03
.§§ 81 ± 06
.77
.71 .78 ± .07
.86
.50
.50 .52 ± .03
_56
.43
.44 .43 ± .01
.43
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Table 2. Analysis of Variance Tables to Test for Differences
Between Well 3, Area 15 Dairy Barn and Building 2105
Source
DF
,xx
Sum of Squares Mean Squares F-Statistic Significance
First Set of TLD's
Mean 1 1.6044 1.6044
Among Locations 2 .0431 .02155
*2105 vs. Others 1 .04302 .04302
Remainder 1 .00008 .00008
Within Locations (Error) 6 .0083 .001383
Total 9 1.6558
Second Set of TLD's
Mean
Among Locations
2105 vs. Others
.. Remainder
Within Locations (Error)
Total
Both Sets of TLD's
Mean 1 2.7300 2.7300
Among Locations 2 .0686 .0343
2105 vs. Others 1 .06847 .06847
Remainder 1 .00013 .00013
Between Sets 1 .0193 .0193
Locations x Sets 2 .0014 .0007
Error 12 .0109 ,00091
1
2
1
1
6
9
1.1449
.0269
.02645
.00045
.0026
1.1744
1.1449
.01345
.02645
.00045
.00043
15.578
30.729
1
31.038
61.512
1
37.692
75.242
1
21.209
.769
.01
.01
NS
01
.01
NS
.01
.01
NS
.01
NS
Total
18
This contrast indicates that the apparent difference among locations was due
to Building 2105 differing from the other two.
xx
Degrees of freedom
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Table 3. Analysis of Variance Tables to Test for Differences
Between Irrigated and Undisturbed Soils
Source DF Sum of Squares Mean Squares F-Statistic Signifiqance
First Set of TLD's
Mean
Between Soils
Within Soils (Error)
Total
1
1
4
2.8428
.1204
,0037
2.9669
2.8428
.1204
.00093
129.462
.01
Second Set of TLD's
Mean
Between Soils
Within Soils (Error)
Total
1
1
4
2.3313
.1472
.0133
2.4918
2.3313
.1472
.0033
44.606
.01
Both Sets of TLD's
Mean
Between Soils
Between Sets
Soils x Sets
Error
1
1
1
1
8
5.1614
.2670
.0127
.0007
.0168
5.1614
.2670
.0127
.0007
.00211
126.540
6.019
.3318
.01
.05
NS
Total
12
5.4587
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