Measurements of air dose rates in and around houses in the Fukushima Prefecture in Japan after the Fukushima accident

福島事故後の福島県における家屋内及び家屋周辺での空間線量率測定

松田 規宏  ; 三上 智   ; 佐藤 哲朗*; 斎藤 公明  

Matsuda, Norihiro; Mikami, Satoshi; Sato, Tetsuro*; Saito, Kimiaki

Measurements of air dose rates in less contaminated areas were conducted in and around houses. The relation of both was summarized as dose reduction factors. For wooden and lightweight steel houses, the dose rates showed a positive correlation and linear regression with a slope-intercept form due to the natural background. The average dose reduction factor was 0.38 on the first floor. The reductions in indoor dose rates are observed because a patch of ground under each house is not contaminated (this is the so-called uncontaminated effect). The characteristics were clarified through Monte Carlo simulations. For reinforced steel-framed concrete houses, the dose rates did not show a correlation. It was found that there is a great variation in air dose rates even within one house, such as the size and shape of a house, construction materials acting as a shield and as sources, position (including height) within a room, floor number, total number of floors, and surrounding environment.