2024 Volume 13 Issue 2 Pages 81-
Ever since the accident at TEPCOʼs Fukushima Dai-ichi Nuclear Power Plant (FDNPP) has passed for 12 years, a part of residents is still concerned about radiation exposure to radionuclides from the environment. In this study, we carried out measurement of the absorbed dose rate in air and assessment of annual effective dose at Kawauchi Village, Tomioka Town, and Okuma Town in Fukushima Prefecture, which are in Hamadori District, to clarify the external exposure dose to the public from artificial radionuclides based on natural radionuclides for use in risk communication with residents. The measurement point was selected in a 2 km × 2 km mesh, and spot measurement and a car-borne survey were conducted using a 3 in × 3 in cylindrical NaI (Tl) scintillation spectrometer. The measurement points were shared using the Global Positioning System. The ambient dose rates in the air from natural radionuclides, artificial radionuclides by spot measurement, and artificial radionuclides by car-borne survey were 0.022-0.069, 0.018-2.394, and 0.001-1.610 µSv h -1 , respectively. The areas with high dose rates contain mountainous areas and areas where decontamination has not yet implemented. The annual effective doses from natural radionuclides at Kawauchi, Tomioka, and Okuma were 0.17-0.35, 0.13-0.28, and 0.15-0.28 mSv, respectively. The annual effective doses from artificial radionuclides in the residential zones at Kawauchi, Tomioka, and Okuma were 0.04-0.29, 0.16-0.70, and 0.31-0.73 mSv, respectively. All the measurement points in the residential zone were below the reference level of 1 mSv in the existing exposure situation reported by the ICRP. This data can be used as background data and the comparison between the past and the present, natural and artificial. It is also useful for the residents and those who are considering returning. This work was supported by the Research Project on the Health Effects of Radiation organized by the Ministry of the Environment, Japan.
