Attempt to evaluate the spatial distribution of close-in fallout through the measurement of 137Cs in soil samples taken under houses built within 1-3 years after the Hiroshima atomic bomb

Abstract

Recently, in relation with enlargement of social compensation for A-bomb survivors, concern on radiation exposure due to close-in fallout has been raised among the people who experienced the black-rain. Radioactive characteristics as well as spatial distribution of the close-in fallout by the Hiroshima A-bomb have not been specified even 60 years after the A-bombing. In this work, measurement of Cs-137 in soil samples under houses built after 1945 has been attempted to evaluate the close-in fallout deposition at the time of Hiroshima atomic explosion. As a result, we detected the low-level Cs-137 in soils under houses. However, problem is how we evaluate the levels of detected 137Cs.