Ecological half-life of radiocesium in surficial bottom sediments of ponds in Fukushima based on in-situ measurements with plastic scintillation fibers

Katengeza, E.*; Sanada, Yukihisa   ; Yoshimura, Kazuya  ; Ochi, Kotaro   ; Iimoto, Takeshi*

The rate of temporal change of radiocesium concentration in bottom sediments is governed not only by its physical decay but also by various ecological processes. In this study, the decreasing trend of radiocesium concentration over wide pond areas of surface sediments (up to 10 cm depth), due to ecological processes, was investigated using plastic scintillation fibers (PSF) and was quantified by the ecological half life. PSF measurements were conducted between 2013 and 2019. Their conversion factors ((Bq/kg)/cps) were obtained by comparison between detected radiation counting rate obtained by PSF and the concentration of radiocesium in sediment cores collected from coinciding positions within the same ponds. A forest catchment pond exhibited the longest ecological half life and may indicate catchment derived radiocesium input as was partly evident in the spatial temporal patterns of radiocesium concentration at this pond's inlet.