7 Table 2 Estimation of Gamma Dose? I. Rongelap IT. Ailingnae II, Rongerik IV. Utirik Approx. time of in commencement 64 H+4to6hr 18 H+4to6hr group 28 157 of fallout H+6.8 hr H+22hr Time of Instrumentreadings Best estimate used in dose of total gamma H+ 50 hr (16 people) 373 mR/hr, H+7 days 175 H+ 28.5 hr (8 men) H +34 hr (20 men) 280 mR/hr, H +9 days 190 mR/hr, H+39 days 69 40 mR/hr, H+8 days i4 evacuation H+51 hr (48 people) H+ 58 hr Started at H+55 hr Completed at H+ 78 hr andthe fallout duration as ~12 hr, with most of the dose delivered early in that period. The times when people were evacuated from the islands are shown in Table 2. 2. Gamma (Whole-Body) Dose The fallout (where seen) resembled snow or mist and was deposited relatively homogeneously so that the individuals on each island were considered to have received about the sameestimated dose of gammaradiation. The children may have had a somewhathigher dose than that calculated for the adults because, being smaller, they were closer to the ground andreceived larger midline doses. This possibility is supported by the higher incidence of early nausea and vomiting and the greater depression of blood elements in the young children. The flimsy houses afforded little attenuation of the radiation. The whole-body doses were calculated from measurements with radiation field survey instruments held 3 ft above the ground, made within a weekafter the detonation, by extrapolation to the time of exposure with the energy Spectrum and decay taken into consideration. Takle 2 shows the calculated gamma doses for the different populations exposed. The degree ofhematological depression that developedlater is consistent with the doses calculated. In view of the 47 geometry of exposure, the midline dosesto individuals were higher than those obtained with the usual bilateral exposure of x-radiation.? 3. Skin Dose The dose to the skin surface was muchgreater than the whole-body gamma dose becauseofthe large amountof beta radiation absorbed bythe st 1. The actual skin doses, although impossible to c ulate, probably amounted to thousandsofrads, calculations dose in air (R) 78 and their rangeof values, due to different amounts of fallout sticking to different areas, accounted for the spotty nature and varying intensity oflesions. The extensiveness of the beta burns in each island groupcorrelated roughly with the amountoffallout visible on their island (see Table 6). Most of the skin dose was dueto fallout deposited directly on the skin, but some was dueto beta radiation from fallout on the ground (estimated at Rongelap to be 2000 rads at the level of the dorsum ofthe feet, 600 rads at hip level, and 300 radsat the head, on the basis of continuous exposure and no shielding).? It was fortunate that the beta radiation had an average energy insufficient to penetrate deeply into the skin and therefore resulted for the most partin superficial beta burns. The average beta particle probably did not penetrate much beyond the basallayer of the skin (~ 100 y). However, since epilation occurred in many people, the region of the hair follicles must have received a dose equivalentat least to the minimalepilating dose of 400 rads of 200-kVp x rays. 4. Internal Dose Calculations Internal absorption of radioisotopes was due to inhalation as the radioactive cloud passed over andto ingestion of food and water contaminated with fallout, water probably being a major source. Drinking wateris obtained bycollecting rainfall from the roofs into catchments, anda slight rain was reported on Rongelap the nightofthefallout. Since the cisterns were nearly empty, the dilution effect was minimal. Water was being rationed at that time, and it was drunk in spite of warnings from the health aide. On Rongerik food and water were better protected from fallout deposition. Internal levels of radioisotopes absorbed from the fallout were assessed by numerous radiochemi- Mae _ designation No. ee de ee. Group