Indoor radiocaesium contamination in residential houses within evacuation areas after the Fukushima nuclear accident.

Indoor contaminants were investigated from July 2013 to January 2015 within ninety-five residential houses in five evacuation zones, Iitate village, Odaka district, and the towns of Futaba, Okuma, and Tomioka. A dry smear test was applied to the surface of materials and structures in rooms and in the roof-space of houses. We found that (134)Cs and (137)Cs were the dominant radionuclides in indoor surface contamination, and there was a distance dependence from the Fukushima Daiichi nuclear power plant (FDNPP).

Reduction factors for wooden houses due to external γ-radiation based on in situ measurements after the Fukushima nuclear accident.

For estimation of residents' exposure dose after a nuclear accident, the reduction factor, which is the ratio of the indoor dose to the outdoor dose is essential, as most individuals spend a large portion of their time indoors. After the Fukushima nuclear accident, we evaluated the median reduction factor with an interquartile range of 0.43 (0.