Calibration
Two soil samples, in which 241Am concentrations had been previously determined in the
laboratory, were taken to Ursula and several measurements taken with the samples in place. The
samples were removed and reinserted into the holder each time a count was taken.
The results are given in Table B-6-1. The soil samples used in the calibration were composed of dry
soil, previously calibrated in the EIC laboratory.
For a simple estimate of the uncertainty of the results, we assume + 1 pCi/g 241.4m or + 15%,
whichever is greater, assuming a 5 minute count and low background. If weight and moisture
eontent are not known, the uncertainty increases.
After many samples have been counted by the IMP and processed by lab analysis, it is intended that
an addendum in this Tech Note be prepared, summarizing the comparisons.*
Testing
Soil samples were counted at the Cape Mixan site and the IMP shed as well as truck samples at
Kickapoo. The system seems to work adequately as designed. The following are observations,
suggestions and recommendations in regard to applications of the technique:
1.
Soil samples should be counted in an area where the 137Cs and 60Colevels are low. At the
Cape Mixan area levels were high producing background counts under the 241Am peak of 400
counts. Background at the IMP shedis about 20 counts in 5 minutes,
2.
Dry soil in the petri dish must be estimated or measured. Currently, we are estimating 100
grams while we are waiting for a scale to be delivered.
3.
To determine soil content above or below 400 pCi/g TRU for truck samples, a counting time of
150 seconds is adequate.
TABLE B-6-1. CALIBRATION RESULTS OF IMP SOIL SAMPLE COUNTING SYSTEM
IMP I, Detector 496
Soil Sample
pCi
Net Count
IMP II, Detector 513
in 2414M
Ratio
Peak (5 min)
pC i/count
pCi
11.43
11.83
11.31
12.07
12.90
12.04
11.37
11.20
10.77
4,479
4,479
4,479
4,479
4,479
4,479
10,895
10,895
4,479
4,479
4,479
4,479
4,479
4,479
4,479
953
921
396
371
350
372
394
400
416
SoilSample
Average = 11.66 + 0.63
Net Count
in 2414m
Ratio
Peak (5 min)
pCi count
426
446
512
486
456
436
Average = 9.77 + 0.67
*See Tech Note 6.1.
B-6-2
10.51
10.04
8.75
9.22
9.82
10.27