Investigation of Radioactivity Distribution Inside and Outside Houses Suffered the Fukushima Dai-Ichi Nuclear Power Plant Accident

Enormous amounts of radionuclides were released into the air by the Fukushima Dai-ichi Nuclear Power Plant accident, and some of them penetrated to houses. Understanding the radioactivity distribution inside and outside a house is useful for dose assessment from indoor and outdoor radionuclides. The radioactivity distribution was investigated on two houses in Okuma town, which is located in the difficult-to-return area in Fukushima Prefecture. In October, 2019, the house material samples, such as floor (carpet, tatami mat, wooden flooring), indoor and outdoor wall, ceiling, glass wool covering the attic floor, and roof (clay tile, slate), were collected. The radioactivity in the samples were measured using a high-purity germanium detector. Before the measurement, the top surface area of the samples was also measured. The surface density (Bq m⁻²) was calculated by dividing the radioactivity in the sample by the top surface area. The surface density in thick samples, such as the floor materials, glass wool, roof materials, and soil, could include the radioactivity penetrating into the material as well as one on the surface of the material.