Evaluation of the accuracy of in-situ waterbed radioactivity measurement technology

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

Since 2013, a plastic scitillation fiber (PSF) system has been used for in-situ monitoring of the distribution of radiocesium (Cs and Cs) concentration in bottom sediment of ponds affected by radioactive fallout from the 2011 Fukushima Daiichi Nuclear Power Plant accident. This study aimed at evaluating the stability of the PSF measurements over time in consideration of radiocesium's vertical migration. Relative deviation (RD) of radiocesium concentration estimated by PSF measurement to that measured in sediment core samples with different thickness (10, 15 and 20cm) were calculated. The mean, median, standard deviation and normilized mean square error of the RD increased with core thickness indicating increased overestimation by the PSF as a result of averaging over larger sediment thickness of heterogeneous concentration.