= Be tree Sepee A pitt Paes Ate Cae wt va . a aa ot ee ee . tee a acat + ey Medical Survey of Jopanese Exposed to Fall-out Radiation in 1954 * woos A Report after 10 Years On | March 1954 a thermo-nuclear test explosion was performed at Bikini lagoon by U.S. three ways: (1) From the radioactive materials adhering to the body surface. Externally from the radioactive materials (2) boat, the 5th “ Fukuryu-maru” (Lucky Dragon) (3) Internally from the radioactive materials and heard a detonation sound several minutes later while they were fishing for tunas. After this explosion, a large amount of radio-active substance fell on the neighbouring area. At about 7:00a.m. white matter began to fall, which continued for approximately 5 hours. They gave up fishing and returned to their harbour on 14 March 1954. After landing, all the fishermen were found to have been injured by the radioactive materials. Seven of them were hospitalized to the Tokyo University Hospital, and the other sixteen to the First National Hospital of Tokyo by 28 March. They were discharged from both hospitals in May 1955, except one fatal case who died on 23 September 1954. After being discharged, they took rest at their 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 situations 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 Wehave reported medical data of these people several times'’””. The following is a brief summary of the past findings. A. State of Irradiation and the Estimated Dose The persons were irradiated in the following entering various organs. The diameter of the fall-out materials ranged 19-460, mainly 100-4004". The radiochemical analysis of the materials was performed at several laboratories. According to data from Prof. Kimura’s laboratory”, on 26 March rare-earth elements contributed about 509 of the total radioactivity and uranium contributed about 20%. The specific activity of the material was 0.37 mCi/g on 23 April. By extrapolation of this data, a value of 1.4Ci/g was obtained as the specific activity at 7:00 a.m. on 1 March. The estimation of irradiation dose, especially that from body surface and internally deposited radioactive materials, was difficult. However, externally irradiated dose for 14 days was estimated as 170-700R, about half or mcre being irradiated on the Ist day (Table 1). This estimation was based on the results of the experimental reproduction of ash-fall, and on detailed investigation of each patient’s behaviour on the boat. The dose to cach person differed depending on his behaviour and the position of his calin. The integrated dose to the thyroid from '"I 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 wecks 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 f ve! ee ee ee go was about 90. miles east of the explosion centre. The twentythree Japanese fishermen on board, aged18-39, saw a huge red light in the west deposited in the cabins, on the deck,ete. mae pet. et ots SUE 5 authorities. At that time, one Japanese fishing : Introduction POORERGNIRrE OG em toes er te: * A Tlor, ‘g! iv) lL.