DETERMINATION OF THE PLUTONIUM TO AMERICIUM RATIO IN SOIL SAMPLES FROM ISLAND PEARL DOE/ERSP TECH NOTENO,2.0 DATED: 12 November 1977 AUTHOR: B.Friesen, DRI Soil surface samples were collected on Island Pearl in accordance with documented guidelines, The Samples were analyzed by wet chemistry methods as well as alpha and gamma spectroscopy techniques in the Eberline Instrument Corp. laboratory and the the results forwarded to DRI. The objective was to incorporate the Pu/Am ratio into computations required to make estimates of the Pu distribution on the island based on the 2414m measurements madeby the in situ van (IMP). Use of the ratio is necessary because direct field measurements cannot be made of plutonium by the IMP but they can be made of 241 Am which bears a functional relationship to plutonium. Analysis of the soil sample data involves two steps. First is the determination of a ratio, or if necessary, a set of ratios that can be used to characterize the Pu to Am relationship. The second is the determination of the error term(s) associated with the computed ratio(s), The remainder of this Technical Note will deal with these steps separately. Determination of one mean ratio for Lujor was made first excluding the 238pu component, then later including 238py along with 239,240py, Using 239,240pu and 241A4m_ laboratory results, the ratio was determined for each of 10 samples taken from 5 locations on the island, The arithmetic mean of these 10 numbers was 3.77 with a coefficient of variation of 35.93%. Some concern was expressed over the magnitude of the spread between lowest and highest ratios; the range was from 1.78 to 6.00. Simple and weighted mean ratios of 239,240py to computed for each of 6 arrangements of the data as shown below. "A" Samples Ratio No, 1 3 5 7 ) Simple Mean Weighted Mean Set or Subset Nos. 1-10 1-8 3-8 3-10 241Am were "B" Samples Ratio Ratio No. 1.78 3.10 3.99 3.73 6.00 Ratio 2 4 6 8 10 1.78 4.64 3.80 3.59 5.30 3.72 3.96 3.82 4.00 Weighted 3.98 3.43 3.83 4.36 Mean Simple 3017 3.30 3.80 4.26 Attention was then directed toward a comparison of surface soil ratios and subsurface ratios taken at 10 cm and 20 em depths. All tests performed indicated that in the statistical sense all of the ratios came from the same population, i.e., there was no reason to discard or suspect any of the numbers, taking them at face value. It was recognized that some outside information not evident in the data could lead to later changes; however, the decision was made to proceed with available data for a first approximation. The ratio actually used in preparing the first estimates of 239,240py for Pearl was 3.825 + .495. B~2-1