抄録
Large amounts of radiocesium were released into the environment by the Fukushima Daiichi nuclear power plant accident in Japan in March, 2011. In this study, the vertical distribution of radiocesium in the side bar deposits of two rivers that originate in Fukushima Prefecture, the Utsushi and Agano Rivers, was determined and the transportation of radiocesium was discussed. The side bar deposits comprised sandy and muddy layers; the latter layer tended to have higher radiocesium concentrations. The concentration of radiocesium per clay fraction was calculated by dividing the concentration of radiocesium per fine earth fraction (particle diameter ≤ 2 mm) by the clay content. The concentration of radiocesium per clay fraction was high in the lower layers of the side bar that appears to have been deposited shortly after the nuclear power plant accident. Subsequently, the concentration of radiocesium per clay fraction tended to decrease with the deposition of sediment. In addition, in the lower layer of the Utsushi River side bar, significant radioactivity was detected in the weathered biotite particles of the sand-size fraction.
