Estimation of the vertical distribution of radiocesium in soil on the basis of the characteristics of -ray spectra obtained via aerial radiation monitoring using an unmanned helicopter

Ochi, Kotaro   ; Sasaki, Miyuki  ; Ishida, Mutsushi*; Hamamoto, Shoichiro*; Nishimura, Taku*; Sanada, Yukihisa   

After the Fukushima Daiichi Nuclear Power Plant accident, the vertical distribution of radiocesium in soil has been investigated to better understand the behavior of radiocesium in the environment. The typical method used for measuring the vertical distribution of radiocesium is troublesome because it requires collection and measurement of the activity of soil samples. In this study, we established a method of estimating the vertical distribution of radiocesium by focusing on the characteristics of -ray spectra obtained via aerial radiation monitoring using an unmanned helicopter. In this method, the change in the ratio of direct rays to scattered rays at various depths in the soil was utilized to quantify the vertical distribution of radiocesium. The results show a positive correlation between the abovementioned and the actual vertical distributions of radiocesium measured in the soil samples.