We investigated the time series data of environmental radiation from monitoring posts, widely set both inside and outside of Fukushima Prefecture since the accident of the Fukushima Daiichi Nuclear Power Plant following to the Northeast Japan Great Earthquake in 2011. Our investigation showed that radioactivity spread from the nuclear reactors have decreased to nearly the same level as natural radiation levels possibly due to chemical diffusion and radioactive decay. However, in granitoid areas such as the Abukuma Mountains, natural radioactivity from potassium and uranium in basement rocks can raise natural radiation level there. On the other hand, environmental radiation dose generally increases at rainfall. In contrast, it was not the case in the radiation levels observed by monitoring posts in Fukushima City, approximately twice as high as those in other areas, regardless rainfall. Therefore, we conclude the present difference of environmental radiation levels among Fukushima Prefecture seems to be controlled in two factor level by local geology, approximately.
東北地方太平洋沖地震以降の福島県内のモニタリングポストの放射線計測データの解析
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