STORAGE AND MIGRATION OF FALLOUT SR-90 AND CESIUM-137 FOR OVER 40 YEARS IN THE SURFACE SOIL OF NAGASAKI

The vertical migration of Sr-90 and Cs-137 produced by the explosion of the atomic bomb in 1945 was investigated in an unsaturated soil layer in the Nishiyama area of Nagasaki. The in situ migration rates of Sr-90 and Cs-137 were estimated to be 4.2 mm yr-1 and 1.0 mm yr-1, respectively, when the rate of movement of soil water was 2500 mm yr-1. The in situ K(d) values of Sr-90 and Cs-137 were calculated to be 0.3 m3 kg-1 and 1.2 M3 kg-1, respectively. These are probably the only results that exist for the interaction between soil and Cs-137 and Sr-90 over 40 yr. These results suggest that since fallout Cs-137 and Sr-90 have remained in the surface soil for a long period of time, we should pay significant attention to radiological effects of nuclear accidents such as the Chernobyl disaster.