2024 Volume 13 Issue 2 Pages 82-
We are conducting a research project on dose assessment for residents in the coastal area of Fukushima Prefecture. This project estimates annual effective doses from inhalation, ingestion and external exposure. These dose estimates cover both artificial radionuclides, such as radiocesium, and natural radionuclides. The doses from both sources will be compared to enable the local population to assess the influence of the FDNPP accident on the total dose. We have selected three coastal communities: Kawauchi Village, Tomioka Town and Okuma Town. In this presentation, we would like to show the results of indoor and outdoor radon and thoron progeny concentrations, as well as atmospheric 137 Cs concentrations. Indoor radon concentrations are measured in 70 dwellings (every 30 dwellings in Kawauchi Village and Tomioka Town and 10 dwellings in Okuma Town) using radon-thoron discriminative monitors (RADUET, Radosys, Hungary). In addition, passive radon and thoron progeny monitors (progeny monitor) are installed in each house along with the RADUETs. These monitors will be replaced every three months for one year in order to assess the annual effective dose, taking into account the seasonal variation of each concentration. We have selected the two locations in each municipality for outdoor radon measurements using RADUETs. Airborne dust is collected using a high-volume sampler at 500 L/min for 24 hours, and then 137Cs concentrations are measured using a HPGe detector. The annual means of indoor radon concentrations in Kawauchi Village, Tomioka Town and Okuma Village were evaluated to be 20 ± 10, 18 ± 12 and 19 ± 16 Bq/m3, respectively. In addition, the annual means of EETC in each municipality were evaluated to be 1.1 ± 1.1, 0.4 ± 0.3 and 0.8 ± 0.8 Bq/m3, respectively. On the other hand, the concentrations of radon and 137 3 Cs in the atmosphere at six measurement sites were estimated to be 7 ± 4 Bq/m and 44 ± 54 μBq/m3, respectively. The annual effective doses due to inhalation of natural (radon and thoron) and artificial ( 137 Cs) radionuclides were estimated to be 0.81 mSv and 1.1 nSv, respectively. Thus, the contribution of annual effective doses due to airborne artificial radionuclides are quite small compared to the natural sources. We will summarise the comprehensive doses from natural and artificial components to enable better radiation risk communication to residents. This work is supported by Research Project on the Health Effects of Radiation organized by Ministry of the Environment, Japan.
