Distribution of plutonium and cesium of fallout from atomic bomb in Nagasaki

To obtain distance distribution of 137Cs levels, the levels of 137Cs were measured using soils used in the measurement of 239,240Pu performed during the period September-November 1990. The sampling areas were 70 located within a radius of 15 km from the hypocenter. Five areas 15 km westward from the hypocenter served as controls (background radioactivity). The levels of 239,240Pu and 137Cs were expressed as MBq/km2 of area. The levels of 239,240Pu were significantly higher in 18 areas than the background. The distribution of 239,240Pu was confirmed to be located in the shape of an unfolded fan between 15deg eastward and 10deg southward. The levels of 137Cs were significantly higher in 4 areas eastward from the hypocenter. Distance distribution of 137Cs was estimated; the areas contaminated with fallout were compared with spatial dose rates measured within several months after A-bombing. Exposure doses from fallout corresponded well to the levels of 239,240Pu and spatial dose rates. (N.K.)