| Co-Investigator(Kenkyū-buntansha) |
ENDO Satoru Faculty of Engineering, HIROSHIMA UNIVERSITY, Associate Professor, 工学部, 助教授 (90243609)
TAKADA Jun Research Institute for Radiation Biology and Medicine, HIROSHIMA UNIVERSITY, Associate Professor, 原爆放射能医学研究所, 助教授 (00274134)
OHTAKI Megu Research Institute for Radiation Biology and Medicine, HIROSHIMA UNIVERSITY, Professor, 原爆放射能医学研究所, 教授 (20110463)
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| Research Abstract |
Atomic bomb doses for the survivors in Hiroshima and Nagasaki have been estimated according to the Dosimetry system 1986 (DS86), which was approved by the effort of US-Japan joint study. The system was used in Radiation Effects Research Foundation (RERF) and Research Institute for Radiation Biology and Medicine, Hiroshima University (RIRBM) and evaluated organ doses of the survivors in their own cohort study. After the determination of DS86 we found discrepancy between the data obtained from neutron activation data and calculation based on DS86. The discrepancy was found in all of the Eu-152, Co-60, Cl-36 and P-32 data, similarly. The largest discrepancy was found in the Hiroshima data. For example, data are 5 to 10 times larger than DS86 at the 1500 m ground distance. Our study was to find its reason and to get a solution. The problem include (1) problems in data taking process, (2) in neutron transport calculation and (3) in the calculation of the process of explosion and deduced neu
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tron source term. We verified that there were no problems in the data taken at short ground ranges and in the transport calculation. About the data taken at long range may have some problems, since gamma rays measured were very low level? For that problem we made simulation calculation using random numbers and found there may be contamination gamma rays included. From the gold activation and monitoring post data taken at Tokai-mura accident, which recently happened, it was verified that thermal and first neutron data and calculation had good agreement until 2000m ground range. Therefore I considered that the problem is in the neutron source term at Hiroshima atomic bomb. I made many calculation based on the model atomic bomb, which reproduce the Hiroshima type atomic bomb, and found the data and calculation agrees if I assume (1) bottom of the atomic bomb came off as if it had about 3cm parallel spacing, (2) about 90m elevation of the neutron emission height (after the emission bomb fell down 90m and formed fire ball), (3) increase the yield about 20%. US group did not accept such assumptions. However, Dr.Kaul in May 2000 at the workshop held at RERF, agreed that we couldn't adjust the calculation and data without such assumptions. We will have a meeting again this May 2001. US-group promised that they would bring their way to solve the problem. There we will discuss this problem and hope that we will have our whole agreement and that we will obtain new dosimetry system for the atomic bomb survivors. Less
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