Appendix II DOSE ASSESSMENT* A. Early Radiation** l. 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 di- rect 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. of an unpredicted shift in the winds in the upper atmosphere, Because 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 entirely 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, “7 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. Table 1 shows Estimated gamma exposure (measurements in air). Instrument No.* Atoll people’ Rongelap Ailingnae Rongerik Utirik Approx. time Time of fallout began evacuation 64 H+4 to 6 hr 18 28 H+4 to 6 hr H+6.8 hr 4H+50 hr (16 people) H+51 hr (48 people) H+58 hr H+28.5 hr (8 men) H+22 hr Started at H+55 hr 157 H+34 hr (20 men) readings (mR/hr) Est. Y exposure (R) 375, H+7 days 175 100, H+9 days 280, H+9 days 69 78 40, H+8 days 14 *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 progress at Brookhaven National Laboratory. Incomplete results give some indication that the previously estimated thyroid doses may be too low. Since the results are preliminary, they are not included in this report. - 116 -