Enrichment of 1291 in Bikini ash could have occurred independently without enriching 23re or 1327, with the result that an !29y comparison between Bikini ash and archival soils was invalid. In conclusion, measurements on archival soils for Eu and 137¢s were in good agreement with Bikini ash and hypothetical_results. The level of !29t in archival soils does not equate with the level of 1297 estimated by other methods nor does it equate with a reasonable extrapolation of the levels of other iodine isotopes. D. Thyroid Absorbed~Dose Estimate Based on Bikini Ash 1. Surface Activity and Exposure-Rate Estimates a. The Nuclide Composition. Radiochemical analysis results for the BRAVO fallout are summarized in Table 9. Bikini ash fell on the Japanese fishing vessel, the 5th Lucky Dragon, on the day of the test. Its gross beta activity was measured and normalized to day 26, and individual nuclide beta activity was identified and quantified by Japanese scientists (Ya56, Ts55). The percent of fallout beta activity, due to fission products present on day 26 after formation, is tabulated in Table 9. The hypothetical beta activity is based on a fallout composition unaltered due to chemical or physical mechanisms affecting certain fission product nuclides. This unaltered composition, which is referred to as unfractionated, was calculated from data given by Crocker. (Cr65). The comparison between Bikini ash beta activity and unfractionated fission product beta activity required conversion of the Yamatera andTsuzuki data sets ¢Ya56, Ts55) into percent fission product beta activity. That is, we exclude the beta activity of the activation products 35g, 45¢a and the transuranic nuclide 237u for comparison purposes. We assumed that 237, which represented 20% of the beta activity on day 26 in the Tsuzuki data, represented 20% of the beta activity in the Yamatera data. The column in Table 9 headed "U-238TN Unfractionated % Fission Product Beta Activity" represents the hypothetical percent of selected unfractionated fission products following thermonuclear neutron fission of 238y, The data are applicable to day 26 post-detonation. The thermonuclear neutron energy spectrum and uranium target were chosen to represent the BRAVO device (0C68). The difference between percentages based on the Japanese measurements and those based on the hypothetical beta activity from thermonuclear fission represents differences between fractionated and unfractionated fallout. As previously implied, the term fractionation indicated alterations of nuclide composition in fallout debris. The ratio of two nuclides in fallout was often used to describe fractionation quantitatively (Fr6l1). The denominator of the ratio was taken to be the activity of 957eNb (Fr61). To quan- tify fractionation between two nuclides, the beta activity ratios were compared by Freiling (Fr61). He uses the term "degree of fractionation" to represent the range of variability of the nuclide ratio. The term "extent of fractionation" represented the portion of the total nuclide produced in the fallout cloud which departed from the unfractionated ratio. -19 -