THEN Medical Survey of Japanese Exposed to Fall-out Radiation in 1954 A Report after 10 Years |. three ways: (1) From the radioactive materials adhering Introduction On | March 1954 a thermo-nuclear test explo- sion was performed at Bikini lagoon by U.S. authorities. At that time, one Japanese fishing boat, the 5th “ Fukuryu-maru” (Lucky Dragon) was about 90 miles east of the explosion centre. The twentythree Japanese fishermen on board, aged 18-39, saw a huge red light in the west and heard a detonation sound several minutes later while they were fishing tor tunas. After this explosion, a large amount of radio-active substance fell on the neighbouring area. At about 7:00 a.m. white matter began to fall, which continued for approximately 5 hours. They gave up fishing and returned to their harbour on I4 March 1954. After Janding, all the fishermen were found to have been injured by the radioactive materials. The diameter of the fall-out materials ranged 19-460 «, mainly 100-400,"'. The radiochemical analysis of the materials was performed atseveral laboratories. According to data from Prof. Kimura's laboratory”, on 26 March rare-earth elements contributed about 50% of the total radioactivity and uranium contributed about 205. The specific activity of the material was 0.37 mCi/g on 23 April. By extrapolation of this data, a value of 14Ci/g was obtained as the specific activity at 7:00a.m. on 1 March. from body surface and internally deposited mated as home for some period. Although some of them continued to work as fishermen, most of them gave up fishery and got new jobs. Because of their varied status in occupations, financial situa- tions and of the widely distributed addresses, it was not always possible to get all of them together for the annual examinations as planned. i. Summary of the Past Findings We have reported medical data of these people several times’’"”. The following is a brief sum- mary of the past findings. A. State of Irradiation and the Estimated Dose The persons were irradiated in the following The estimation of irradiation dose, especially that March. They were discharged from both hos- After being discharged, they took rest at their AAG 5 Internally from the radioactive materials entering various organs. radioactive materials, was difficult. died on 23 September 1954. SS (3) to the body surface. Externally from the radioactive materials deposited in the cabins, on the deck, ete. Seven of them were hospitalized to the Tokyo University Hospital, and the other sixteen to the First National Hospital of Tokyo by 28 pitals in May 1955, except one fatal case who moni (2) However, externally irradiated dose for 14 days was esti- 170-700 R, about half or more being irradiated on the Ist day (Table 1). This estima- tion was based on theresults of the experimental reproduction of ash-fall, and on detailed investigation of each patient’s behaviour on the boat. The dose to each person differed depending on his behaviour and the position of his cabin. The integrated dose to the thyroid from '"] was inferred as about 20-120 rad on 4 persons who were examined 2-3 times for external countings of radioactivity in the thyroid region during the 4-7 weeks after the initial exposure. Urine samples of patients were collected and transferred to the Health and Safety Laboratory of U.S. A. E.C. for radiochemical analysis several times.’ Significant amounts of radioactivity were found in the urine samples collected at about 4 weeks after the explosion. Radiochemical analysis of these samples indicated that “Sr and