FCLS-H 23 November 1976 MEMORANDUM FOR RECORD SUBJECT: Determination of Pu in Enewetak Soil by Alpha Particle Counting REFERRENCE: Memorandum for Record, 27 Oct 76, Same Subject 1. Ref 1 reported interim results of a study to compare alpha particle count rates of Enewetak soil samples with their total specific alpha particle activity as determined by radiochemistry and reported in NVO-140. A reasonably good correlation was determined for 11 of 13 samples investigated. Since alpha particle count rates for the two "outliers" was reproducible, and their Pu content appeared too large, both samples were reanalyzed for Pu at USAF/MCL by radiochemistry. Results are as follows: SAMPLE NUMBER _ 5116 5196 2. NVO-140 Pu CONC (pCi/g) 399 532 REVISED Pu CONC (pCi/g) 278 65 NVO-140 Am CONC (pCi/g) TOTAL SPECIFIC _ 19.00 9.65 a ACTIVITY 297.0 74.7 Enclosure 1 tabulates the net alpha particle count rates and total specific activities for all 13 samples. The average count rate per unit specific activity was determined both as the ratio of the means, By> and the mean of the ratios, Bo: B, + SE = 0.0196 + 0.0019 Relative SE = 9.82% B. + SE = 0.0302 + 0.0075 Relative SE = 24.8% A linear regression yielded the relationship: Y(c/min) = 0.433 + 0.0169 X(pCi/g) with a coefficient of determination, r2 = 0.9525. This curve is plotted in enclosure 2 as a broken line. All data points are shown in enclosure 2 within circles, and the solid line is a plot of Y = B,X. 3. Alpha particle counting (without chemistry) continues to look suitable as a rapid method for estimating-*the concentration of transuranics in Enewetak soil at concentration levels of interest to Cleanup. A possible explanation for the high Pu concentrations reported in NVO-140 for samples 5116 and 5196 is that (710g) aliquots contained "hot particles" and the