Evaluation of ambient dose equivalent inside and outside houses in Fukushima using in-situ gamma-ray spectrometry with unfolding technique

Hayashi, Masateru*; Makita, Taisuke*; Azuma, Tetsushi*; Sasano, Makoto*; Yoshida, Hiroko*; Tsuda, Shuichi  

Evaluation of dose rates of artificial nuclides is of importance to make a decision on return of residents to their hometown contaminated by the Fukushima Daiichi Nuclear Power Plant accident. This study applies an unfolding method to measured data by a NaI(Tl) detector in/outside houses, and obtained gamma-ray energy spectra. We calculated ratios of dose rate from natural nuclides such as 40K and Uran-Thorium series to those of artificial nuclides. It was found that the ratios are almost constant, given that no artificial nuclide exists. This means a possibility that dose rates of artificial nuclides can be precisely estimated by subtracting dose rates of natural nuclides.