Table 2 Estimation of Gamma Dose2 No. in Approx. time of commencement I. Rongelap 64 H+4to6hr II. Ailingnae III. Rongernik 18 28 H+4to6hr H+6.8 hr Group designation [V. Ctirik group. 157 offallout H+22? hr Timeof evacuation H +50 hr (16 people) H+51 hr (48 people) H+58 hr H+ 28.5 hr (8 men) H +34 hr (20 men) Started at H+ 35 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 shownin Table 2. 2. Gamma (Whole-Body) Dose Thefallout (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 same estimated 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 incidenceof early nausea and vomiting and the greater depression of blood elements in the young children. The flimsy houses affordedlittle 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, bv extrapolation to the time of exposure with the energy spectrum and decay taken into consideration. Table 2 shows the calculated gammadoses for the different populations exposed. The degree of hematological depression that developed lateris consistent with the doses calculated. In view of the 47 geometryof exposure, the midline doses to individuals were higher than those obtained with the usual bilateral exposure of x-radiation.? 3. Skin Dose The dose to the skin surface was much greater than the whole-body gammadose becauseofthe large amount ofbeta radiation absorbed by the skin. The actual skin doses, although impossible to calculate, probably amounted to thousands ofrads, Instrumentreadings used in dose Best estimate of total gamma 375 mR/hr, H +7 days 175 100 mR ‘hr. H+9 davs 280 mR/hr, H+9 days 69 78 40 mR/hr, H +8 days l+ calculations dose in air (R) andtheir range of values, due to different amounts offallout sticking to different areas, accounted for the spotty nature and varyingintensity oflesions. The extensiveness of the beta burns in each island group correlated roughly with the amountoffall- out 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 of the 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 part in superficial beta burns. The average beta particle probably did not penetrate much beyondthe basal layer of the skin (~ 100 4). However,since epilation occurred in many people, the region of the hairfollicles must have received a dose equivalent at least to the minimal epilating 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 majorsource. Drinking wateris obtained by collecting rainfall from the roofs into catchments, anda slight rain was reported on Rongelapthe night ofthe fallout. 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-