Appendix II DOSE ASSESSMENT* A. Early Radiation** 1. Source The ionizing radiation exposure of the Marshallese was due entirely to fallout, since the detonation site was too far away for thermal, blast, or direct irradiation effects. (In contrast, direct effects were responsible for all the injuries from the atomic bombs in Hiroshima and Nagasaki, with little or no fallout.) The fireball from the 1954 Bravo device, detonated from a tower, touched the surface of the earth at Bikini, and large amounts of mate- rial were drawn up and mixed with fission products in the bomb cloud. Because of an unpredicted shift in-the winds in the upper atmosphere, fallout was deposited in a cigar-shaped area 20 to 40 miles wide extending 4200 miles to the east of Bikini (see Figure 1 in the text). The radioactivity was due to fission products and some neutron-induced radionuclides; little fissile material was noted. The radiation was therefore almost entireiy from gamma and beta rays of varying energy from numerous neutron-rich radionuclides. The time after detonation when fallout began was estimated as 4 to 6 hr at Rongelap, v7 hr at Rongerik, and 22 hr at Utirik, and the fallout duration as 12 hr, with most of the dose delivered early in that period. fallout exposure data on the atolls. Table 1. No.* Atoll people Rongelap Ailingnae Rongerik Utirik Estimated gamma exposure (measurements in air). Approx. time Time of fallout began evacuation 64 H+4 to 6 hr 18 H+4 to 6 hr 4H+50 hr (16 people) H+51 hr (48 people) #8+58 hr H+22 hr H+34 hr (20 men) Started at H+55 br 28 157 Table 1] shows H+6.8 hr H+28.5 hr (8 men) Instrument readings (mR/hr) Est. Y exposure (Rk) 375, H+7 days 175 100, H+9 days 69 40, H+8 days 14 280, H+9 days 78 *Does not include people exposed inutero. *Dr. S$.H. Cohn (Medical Department, BNL) and Messrs. E.T. Lessard, N.A. Greenhouse, and R.P. Miltenberger and Dr. J. Naidu (Safety and Environmental Protection Division, BNL) assisted with this Appendix. **A reevaluation of the early whole-body and internal organ doses is in prog- ress at Brookhaven National Laboratory. Incomplete results give some indica— tion that the previously estimated thyroid doses may be too low. results are preliminary, they are not included in this report. - 110 - Since the