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KMID : 0364920200450020053
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Journal of Radiation Protection and Research
2020 Volume.45 No. 2 p.53 ~ p.68
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Individual Doses to the Public after the Fukushima Nuclear Accident
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Ishikawa Tetsuo
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Abstract
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Background: International organizations such as the World Health Organization (WHO) and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported public exposure doses due to radionuclides released in the Fukushima nuclear accident a few years after the event. However, the reported doses were generally overestimated due to conservative assumptions such as a longer stay in deliberate areas designated for evacuation than the actual stay. After these reports had been published, more realistic dose values were reported by Japanese scientists.
Materials and Methods: The present paper reviews those reports, including the most recently published articles; and summarizes estimated effective doses (external and internal) and issues related to their estimation.
Results and Discussion: External dose estimation can be categorized as taking two approaches?estimation from ambient dose rate and peoples’ behavior patterns?and measurements using personal dosimeters. The former approach was useful for estimating external doses in an early stage after the accident. The first 4-month doses were less than 2 mSv for most (94%) study subjects. Later on, individual doses came to be monitored by personal dosimeter measurements. On the basis of these measurements, the estimated median annual external dose was reported to be <1 mSv in 2011 for 22 municipalities of Fukushima Prefecture. Internal dose estimation also can be categorized as taking two approaches: estimation from whole-body counting and estimation from monitoring of environmental samples such as radioactivity concentrations in food and drinking water. According to results by the former approach, committed effective dose due to 134Cs and 137Cs could be less than 0.1 mSv for most residents including those from evacuated areas.
Conclusion: Realistic doses estimated by Japanese scientists indicated that the doses reported by WHO and UNSCEAR were generally overestimated. Average values for the first-year effective doses for residents in two affected areas (Namie Town and Iitate Village) were not likely to reach 10 mSv, the lower end of the doses estimated by WHO.
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KEYWORD
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Fukushima Accident, Effective Dose, External Exposure, Internal Exposure, First-Year Dose
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