Enrichment of 129: in Bikini ash could have occurred independently without enriching 129pe@ or 1321, with the result that an 1297 comparison between Bikini ash and archival soils was invalid. In conclusion, measurements on archival soils for !55gu and 13’cs were in good agreement with Bikini ash and hypotheti- cal results. The level of !29t in archival soils does not equate with the level of !297 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 ae The Nuclide Composition. Radiochemical analysis results for the BRAVO fallout are summarized in Table 9. Bikini ash fell on the Japanese fishing vessel, the Sth 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 fissioi product beta activity required conversion of the Yamatera and Tsuzuki data sets (Ya56, Ts55) into percent fission product beta activity. That is, we exclude the beta activity of the activation products 35s, 45ca and the transuranic nuclide 297u for comparison purposes. We assumed that 2374, 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 columm 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 altera~ tions of nuclide composition in fallout debris. The ratio of two nuclides in fallout was often used to describe fractionation quantitatively (Fr61). The de~ nominator of the ratio was taken to be the activity of 957rNb (Fr6l). To quantify fractionation between two nuclides, the beta activity ratios were compared by Freitling (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 -