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Furuta, Takuya; Takahashi, Fumiaki
no journal, ,
After the accident at the Fukushima Daiichi Nuclear Power Station, it became important to assess radiation doses accounting dose reduction by buildings in order to take measures for radiation protection reflecting life-styles of residents according to data of the radiation monitoring in open air. We have been analyzed the radiation dose reduction in buildings standing on a flat ground. However, slopes nearby buildings can be found in many situations of houses in Fukushima area. We performed simulation using PHITS and analyzed radiation dose rates in a wooden house, which is the most popular residential house in Fukushima area, standing nearby a slope. Here, radiation dose rates in the house were computed in a situation where radioactive cesium was distributed homogenously over the ground including the slope and compared with those in the house standing on a flat ground. We found that the variation of the dose rates in the house was not significant with and without the slope. Accordingly, high dose rates possibly found in a house nearby slopes are more likely, for instance, because of contaminated plants at the slopes than due to the geometrical effect of the slopes.
Wakatsuki, Tsuyoshi*; Yamada, Ryuji*; Kokubu, Yoko
no journal, ,
Many soil slips and debris flows on the welded-tuff slopes were induced by heavy rain on July 28, 2013 in Tsuwano, Shimane. The debris flows eroded sidewalls or streambeds in river channels and the sediments driven by earlier slope movements were exposed in places. In six outcrops, we collected 53 dead wood chip samples presumably buried at the sediment deposition, and radiocarbon dating was performed. At around 418 m asl in Nayoshi district, Tsuwano, the outcrops of the black-clayey sediments are found, which are supposed to have deposited in a past dammed lake. They are distributed at upstream of a topographically-estimated deposit zone for an ancient large-scale slope failure, and the calendar-calibrated ages of these sediments ranges from 41 to 55 ka BP. It is therefore conjectured that the slope failure had occurred before 55 ka BP and the dammed lake had burst after 41 ka BP. An average deposition rate of about 0.3 m/1000 y was estimated at an outcrop of the dammed lake sediments