Fig. 8.

Decontamination of the rice field [1,2]. Radioactive Cs was only adsorbed onto the fine clay part of the soil; hence, it took time to sediment when water was introduced to the field and mixed with the surface soil. After mixing the surface soil with water, first the larger particles settled out, but the fine particles remained suspended in the supernatant. At this stage the fine particles suspended in the water were separated off into the ditch prepared next to the farming field, leaving most of the non-contaminated soil behind. Through this method, >80% of the radioactivity was removed: a: before treatment, b: after the removal of the supernatant. The radioactive Cs remained on the bottom or the walls of the ditch and hardly moved. When the ditch was filled in with non-contaminated soil, most of the radioactivity was shielded (M. Mizoguchi et al.).