Satoru Endo, Yuta Taguchi, Kotaro Shiraishi,
Tsuyoshi Kajimoto, Kiyoshi Shizuma
Graduate School of Engineering, Hiroshima University
Tetsuji Imanaka, Satoshi Fukutani
Research Reactor Institute, Kyoto University
Evgeniya Granovskaya, Masaharu Hoshi
Research Institute for Radiation Biology and Medicine, Hiroshima University

Abstract

For the early entrance survivors in Hiroshima and Nagasaki atomic bomb (Abomb),radiation doses from activated materials induced by the A-bomb neutrons are dominant. For estimation of such doses, element concentrations of surrounding materials such as soil and rubbles are necessary. Especially Sc density in soil is important for estimating radiation doses at the time 20 – 30 days after explosion because 46Sc, which has the half-life of 84 days, is considered to be the major gamma-ray emitting nuclide induced by A-bomb neutrons. However, few data of Sc density in soil are available in both of Hiroshima and Nagasaki cities. Purpose of this study is evaluation of Sc density in soil and its uneveness using neutron activation analysis. Soil samples were taken from 10 locations within 4 km from the A-bomb hypocenter in Hiroshima City. And also, one plaster sample under roof-tiles of old Hiroshima house was taken. These samples together with a reference rock sample of JA-1 were activated in Kyoto University Reactor (KUR). Element concentrations were relatively obtained comparing counting rates of gamma-ray peaks of identified radionuclides from soil samples with those from the reference rock by Ge-detectors. Twenty three element concentrations including Al, Mn, Na and Sc were obtained by the activation analysis. The obtained element concentrations were compared with values used in Dosimetric System 1986 (DS86) and found to be roughly the same as those in DS86. Sc density in Hiroshima soil was estimated to be 5.12 ± 0.59 (ppm).It was found the unevenness of Sc density in soils for 10 location of Hiroshima city was about 12%.