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Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively high exposure to natural radiation. The goals of the present study were to characterize exposure of the entire Mamuju region as a high natural background radiation area (HNBRA) and to assess the existing exposure as a means for radiation protection of the public and the environment. A cross-sectional study method was used with cluster sampling areas by measuring all parameters that contribute to external and internal radiation exposures. It was determined that Mamuju was a unique HNBRA with the annual effective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated. The study results are new scientific data allowing better understanding of health effects related to chronic low-dose-rate radiation exposure and they can be used as the main input in a future epidemiology study., 論文

Radionuclide concentrations in environmental samples such as surface soils, plants and water were evaluated by high purity germanium detector measurements. The contribution rate of short half-life radionuclides such as (132)I to the exposure dose to residents was discussed from the measured values. The highest values of the (131)I/(137)Cs activity ratio ranged from 49 to 70 in the environmental samples collected at Iwaki City which is located to the south of the F1-NPS. On the other hand, the (132)I/(131)I activity ratio in the same environmental samples had the lowest values, ranging from 0.01 to 0.02. By assuming that the (132)I/(131)I activity ratio in the atmosphere was equal to the ratio in the environmental samples, the percent contribution to the thyroid equivalent dose by (132)I was estimated to be less than 2%. Moreover, the contribution to the thyroid exposure by (132)I might be negligible if (132)I contamination was restricted to Iwaki City.

A large amount of radionuclides was released from the Fukushima Dai-ichi Nuclear Power Station (FDNPS) following the damage caused by the tsunami due to the Great East Japan Earthquake on 11 March 2011. Although many radionuclides in various environmental samples around the FDNPS have been measured, (3)H in the terrestrial environment has not yet been reported. We present here the first survey results of (3)H concentrations in plant samples collected around the FDNPS in 2011 from shortly after the accident. The free-water (3)H concentrations in herbaceous plant shoots and evergreen tree leaves were considerably higher than the previous background concentration, and diminished with distance from the FDNPS. Although reconstruction of atmospheric (3)H concentrations after the accident is difficult, a rough estimate of the radiation dose due to (3)H inhalation about 20 km from the FDNPS is on the order of a few microsieverts (μSv).