Evaluation of Gamma-ray Spectra Measured Inside and Outside a House in Fukushima

Abstract

Photon spectra were measured inside and outside a house in Minami-Soma city by using a NaI(Tl) scintillation spectrometer. The photons were categorized into three groups according to their energy. The groups were (1) scattered photons, which include low energy photons, (2) direct photons from ¹³⁴Cs and ¹³⁷Cs sources and (3) the other photons. Then the ratios of the ambient dose equivalents H^*(10) of the scattered photons to those of the direct photons from the ¹³⁴Cs and ¹³⁷Cs sources have been evaluated from the measured photon spectra. The ratios are high inside the house compared with those out of the house. It was found that the scattered photons contribute to the H^*(10) by more than 50% inside the house. The ambient dose equivalent average energies of the scattered photons are around 0.25 MeV both inside and outside the house. These data is worthwhile to design the optimum shielding for the protection against the public radiation exposure.