1.1 Nature of the Event and Description of the Exposed Groups FotLowinG THE Detonation of a nuclear device at the Pacific Proving ground in the Spring of 1954, significant amounts of radioactive material fell on neighboring populated atolls. The Marshallese inhabitants of Rongelap atoll (designated as Group I) received the highest calculated dose of radiation. Some of the Rongelap people were located temporarily on Ailinginae atoll from the time of the fallout until they were evacuated (Group II). Their calculated dose was smaller than that of the other members of the parent group. The American service men (Group III) were located on Rongerik atoll. The largest group of Marshallese (Group IV) were located on Utirik atoll and received the smallest dose. The Marshallese were living underrelatively primitive conditions in lightly constructed palm houses (Fig. 1.1). The American military personnel had the second highest exposure. They were more aware of the significance of the fallout than were the Marshallese, and promptly put on ad- ditional clothing to protect their skin. As far as duties would permit, they remained inside of aluminum buildings. In contrast, most of the Marshallese remained out-of-doors and thus were more heavily contaminated by the material falling on the atolls. Some of the Marshallese, however, went swimming during the fallout and many of the children waded in the water, thus washing a considerable amount of the material from their skin. The exposed personnel were evacuated to Kwajalein by air and surface transportation. Since a survey of all individuals showed that there was significant contamination of skin, hair and clothes, prompt decontamination was instituted. Clothes were removed and laundered and repeated washings of the skin and hair with fresh water and soap were carried out. In many of the Marshallese, it was difficult to wash the radioactive material from the hair because of the heavy coconut-oil hair dressing. The exposure groups with individuals involved, the calculated doses of radiation, the probable times of beginning of the fallout and the evacuation times are given in Table 1.1. Table 1.1—Exposed, and Control Unexposed Groups : GRovuP DESIGNATION APPROXIMATE NomeER IN GRrour PteOFCome FALLout Tux oF Evacuation Group I.—Rongelap 64 Group II.—Ailinginae 18 H + 50 hrs. (16 people) H + 51 hrs. (48 people} H + 58 hrs. Group III.—Rongerik 28 H+ 4to6 hrs. H+ 4to6| hrs. H+ 6.8hrs.| Group IV.—Utirik 157 H + 22hrs. Marshallese, Control Group A Americans, Control Kwajalein-American — 117 H + 28.5 hrs. (8 men) H + 34 hrs. (20 men) Started at H + 55 hrs. Completed at H + 78 hrs. DennINDoseCaLeus LATIONS 375 mr/hrs.,H + days 100 mr/hrs., H + days 280 mr/hrs., H + days 40 mr/hrs., H + days BEst EstiMATE OF otal DosE IN AIR (r) 7; 175 9 69 9 78 8 14 105 Total Exposed—267; Total Controls—222 cn on) CZ 3