ITR-16
SOUTHWESTERN RADIOLOGICAL HEALTH LABORATORY
INTRALABORATORY TECHNICAL REPORT
July 24, 1967
IODINE-131 ON VEGETATION: CANNED VERSUS BULK COUNTING
Wayne A. Bliss
Chinese nuclear detonations in late 1966 led to a small amount of radio -
iodine fallout in southern Nevada which was easily detected on vegeta-
tion samples. The Environmental Surveillance Program of the Southwestern
Radiological Health Laboratory was at that time pondering the feasi-
bility of compressing vegetation samples to a standard volume to en-
hance counting sensitivity and facilitate reproducible counting geome-
tries. The Chinese fallout had.deposited roughly 103 pCi/Kg of 131I
on vegetation as determined from sampling in support of the Nash
Event, January 19, 1967. It was concluded that no fresh fission
products in the off-site area at the time were a result of the Nash
Event. On January 26, 1967 three vegetation samples were collected
from each of three locations: 3, 9, and 25 miles southeast of Lathrop
Wells, Nevada along Highway 95. The monitor making the collections
was instructed to choose three or four hundred grams of leafy material
for each sample. These samples were loosely packaged in 14 by 24
inch plastic bags and gamma counted on a 3 x 3 inch Nal(Tl) crystal.
The samples were then compressed into a plastic container 2 inches
in height and 4 inches in diameter and recounted. The samples were
analyzed for iodine-131 and the results, expressed as pCi/Kg at
time of collection, are shown in the attached table.
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Various correlations among the data are shown. It is readily appar-
ent without statistical proof that compressing the samples increased
the count results by only a factor of about two.
Compressing these samples required the efforts of two persons.
With the necessary precautions to prevent cross-contamination,
cost of containers, etc. , the process is expensive. In the bulk pro-
cess, the samples are placed in an additional bag and moved direct-
ly to the counting facility with little time and effort -when compared
to compacting.
Since vegetation sampling is used only for delineating cloud passage
and a rough estimator of milk contamination in routine surveillance,
compaction of samples appears to be unwarranted by these results
for SWRHL off-site surveillance.
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Location
3 miles SE
of Lathrop
Wells, Nevada
9 miles SE
of Lathrop
Wells, Nevada
25 miles SE
of Lathrop
Wells, Nevada
For all
Samples Average
Sample
Number
020317
020318
020319
020320
020321
020322
020323
020324
020325
d
Counting
Geometry
Bulk
Canned
Bulk
Canned
Bulk
Canned
Bulk
Canned
Bulk
Canned
Bulk
Canned
Bulk
Canned
Bulk
Canned
Bulk
Canned
Bulk
Canned
Deviation Ratio Of Ratio Of
Factor Of Of Average Highest Lowest
Greatest Sample Per Canned To Canned To
131 1 Deviation Location Lowest Highest
pCi/Kg Per Location (Canned/Bulk) Bulk Bulk
570 Bulk: 2.00 1.39 2.35 0.89
1010
1140
1190 Canned: 1.33
830
1340
1590 Bulk; 1.42 1.68 3.01 0.82
3370
1360
1310 Canned: 2.57
1120
2160
1410 Bulk: 1.33 1.44 2.42 0.89
2570
1060
1560 Canned: 2.06
1260
1250
1149 1.52 Average=2.59 Average= 0. 87
1751
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