Aya Sakaguchi
Graduate School of Science, Hiroshima University, Graduate School of Science, Hiroshima University
Masaharu Hoshi
Professor emeritus, Hiroshima University
Michio Aoyamai
Meteorological Research Institute
Hiroaki Kato
Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba
Yuichi Onda
Faculty of Life and Environmental Sciences, University of Tsukuba

Abstract

Radiation doses for the atomic bomb survivors in Hiroshima have been calculated for the direct exposure cases within about 2 km range by dosimetry system 2002 (DS02). In this system beta-ray exposure and internal exposure were not included. At that time such portions of the radiation doses were not considered to be significant for risk estimation. However, there are some discussions that the beta-ray exposure may not have been negligible. According to one of the calculations, skin surface doses due to the neutron activated soil dust come up to a few to several hundreds of mGy (Tanaka et al. 2008). The purpose of this study is to measure particle sizes, since soil particles were activated by neutrons and sometimes fission products were attached. These data will be used to estimate such radiation doses. Using these data, we need to calculate the spread of the dust by the shockwave of the atomic bomb explosion and how it fell down to the atomic bomb survivors. We collected two types of samples such as (1) soil used in walls and roofs in old traditional Japanese houses (in Fukuyama city in Hiroshima prefecture) and (2) ground surface soil samples taken from the depth of 0-1 cm and 1-2 cm in the Hiroshima city area. Particle sizes were measured after using 2 mm mesh sieves. Results of the weight average of the traditional Japanese houses were for soil under roof tiles 23.8 μm and for walls 56.0 μm. Those for the ground surface data from 5 places in Hiroshima city area (0-2 cm thickness) ranged from 40.9 to 105.7 μm.