Iv. THYROID ABSORBED DOSE ESTIMATE BASED ON BIKINI ASH AND RESULTS FROM I, IL AND III. A. Surface Activity And Exposure Rate Estimates 1. The Nuclide Composition Radiochemical analysis results for the BRAVO fallout were summarized in Table 1. Bikini Ash, the name of BRAVO fallout given by Yamatera and Tsuzuki (Ya56, Ts56), fell on the Japanese fishing vessel, the 5th Lucky Dragon, on the day of the test. Gross beta activity of Bikini Ash was measured and standardized to day 26 and individual nuclide beta-activity identified and quantified by Japanese scientists. The per cent fission product beta activity expected on day 26 after formation was tabulated in Table 1. The expected beta activity was based on a fallout composition which was unaltered due to chemical or physical mechanisms affecting certain fission product nuclides. unaltered composition was referred to as unfractionated. This This unfractionated composition was calculated from data given by Crocker (Cr65). The comparison be- tween the measured values of Bikini Ash beta activity and per cent unfractionated fission product beta activity required conversion of the Yamatera and Tsuzuki data sets into per cent fission product beta activity, that is, exclusion of the beta activity of the activation products S-35, Ca-45 and the transuranic nuclide U-237. It was assumed that U-237 which represented 20% of the beta activity on day 26 in the Tsuzuki data also represented 20% of the beta activity in the Yamatera data. The data in Table 1 headed "U-238TN Unfractionated % Fission Product Beta Activity" represented the day 26 theoretical per cent of selected unfractionated fission products following thermonuclear neutron fission of U-238. This neutron energy spectrum and uranium target were chosen to represent the BRAVO device (0C68). The difference between Japanese