IMP SOIL SAMPLE COUNTING SYSTEM DOE/ERSP TECH NOTENO.6.0 DATED: May 1978 AUTHOR: Z. Burson, EG&G Introduction There is a need to develop an in-field, soil sample assay screening method to allow operational decisions to be made in (or near) real time. Possible applications are as follows: 1. Subsurface Soil Sampling: When soil sampling is performed below the surface at a particular site, it is desired to define the extent of contamination at all levels (down to 100 em). To do this in one visit an in-field screening method is necessary. 2. Sample Screening: It is desired to screen soil samples as to activity in order to decide on which samples to process in the lab. It appears that at least half of the samples taken have activity below 2 pCi/g 2414m. 3. Truck Sampling: In the future there may be a need to estimate the soil activity in particular trucks in real time. 4. Soil Removal: In the future there may be a need to estimate the activity in soil in real time as an aid to soil removal. The intent here was to develop, test and calibrate a soil sample holder to be used with the IMPs and the associated counting system. It is not intended to ever be used in place of laboratory soil sample counting or for any permanent recordsor certification. Soil Sample Holder Standard soil samples are routinely counted in the laboratory in a plastic petri dish about 9 em diameter and 2 em deep. The petri dish is placed 3 em from the face of the Ge (Li) detector in a counting shield. It was intended that the counting geometry for the IMPs be as close as reasonably achieveable to the laboratory counting system. The soil sample holders, as designed and built, are shown in Figure B-6-1. The lead surrounding the soil sample reduces the 2414m background to negligible levels. The foam rubber allows pressure to be applied to the holder, thus assuring a reasonable consistency in positioning. It is noted, however, that exact, known positioning cannot be achieved; thus inconsistencies of a few percent between soil sample results is to be expected. u gc DETECTOR Be WINDOW | | : fp / i ZL i 4 we “ — aL 4 1 SUM t= : SO \ FOAM RUBBEP NE LFAC we yy Se -—— 12 PLYWOOD - aD COLLIMATOR a .\ — : L _~ ousinc ! . yy SS. [ N 1? prywaco, a SS PETRI DISH (501. SAMPLE eet i | 7 ¢ " a ¥ S 1 i -_— = LOCKING BULT NOT "UO SCALE FIGURE B-6-1. SOIL SAMPLE HOLDER FOR IMP DETECTORS B-6-1