Estimation of radiation-dose rate contributed from artificial radiation sources using the response matrix method. 5

For dose-rate measurements of γ-rays in air near a nuclear power plant by remote monitoring, the authors present a detailed analysis for the calculation procedure of the indicator dose-rate based on the response matrix method. Gamma spectra from the NaI(Tl) scintillation detector of Environmental Radioactivity Research Institute of Miyagi, Japan, are processed to obtain the RM (Response Matrix) dose-rate. Subtracting the estimated BG (Background) dose-rate yields the indicator dose-rate. Fluctuations due to rainfall effect are remarkable. The authors investigated the cause of the fluctuation and found an inadequacy in nuclear-spectral flux table to be used to calculate the background originating from U-decay series. Using a modified table adequate at rainfall, they succeeded to diminish the fluctuation and to obtain more moderate indicator dose-rates. (S. Ohno)