Appendix IT 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 material 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 “200 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 mate- rial 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. Table 1 shows fallout exposure data on the atolls. Table 1. No.* Atoll people Rongelap 64 Ailingnae Rongerik Utirik 18 28 157 , Estimated gamma exposure (measurements in air). Approx. time Time of fallout began evacuation H+4 to 6 hr H+50 hr (16 people) H+4 to 6 hr H+58 hr H+22 hr Started at H+55 hr H+6.8 hr H+51 hr (48 people) H+28.5 hr (8 men) H+34 hr (20 men) Instrument readings (mR/hr) Est. CR) 375, H+7 days 175 100, H+9 days 69 40, H+8 days 14 280, H+9 days Y exposure 78 *Does not include people exposed in utero. *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. - 110 -