Indoor and outdoor radionuclide distribution in houses after the Fukushima Dai-ichi Nuclear Power Plant accident.

Abstract An enormous amount of radionuclides was released into the atmosphere following the Fukushima Dai-ichi Nuclear Power Plant accident, with part of it penetrating houses. Information on radionuclide distribution inside and outside houses is useful for indoor external dose assessments. To investigate the radionuclide distribution, we collected both soil samples around the target houses and house material samples (i.e., floor, inner wall, ceiling, outer wall, and roof) in Fukushima Prefecture in 2019. The activity of the samples was measured using a high-purity germanium detector. The surface contamination densities of the floor, inner wall, ceiling, outer wall, and roof relative to the ground were 3 × 10−3–7 × 10−2, 6 × 10−5–4 × 10−4, 7 × 10−5–3 × 10−4, 2 × 10−3–1 × 10−2, and 4 × 10−3–2 × 10−1, respectively. The relative surface contamination densities varied depending on the surface material, its location, and surface orientation, indicating that these uncertainty factors should be considered in the dose assessment for residents.