Performance of in situ gamma-ray spectrometry in the assessment of radioactive cesium deposition around the Fukushima Daiichi Nuclear Power Plant

Ji, Y.-Y.*; Ochi, Kotaro   ; Hong, S. B.*; Nakama, Shigeo ; Sanada, Yukihisa   ; Mikami, Satoshi   

In situ gamma-ray spectrometry using diverse survey platforms has been conducted in contaminated areas with several dose rate levels around the Fukushima Daiichi Nuclear Power Plant (FDNPP). Six survey sites, including two evacuation zones around the FDNPP, were selected for ground-based gamma-ray spectrometry using HPGe (high purity Ge) and LaBr(Ce) detectors to assess the radioactive cesium deposition in the ground. The diverse levels of radioactivity of Cs were then distributed to six survey sites from 30 to 3000 kBq m in the measurement period of October 2018. A method to directly calculate the depth profile using in situ measurement was introduced so as to have representation over a wide area, and the results were successfully compared with those of sample analysis at one point in the site.