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Impact of decontamination on individual radiation doses from external exposure among residents of Minamisoma City after the 2011 Fukushima Daiichi nuclear power plant incident in Japan: a retrospective observational study.

J Radiol Prot. 2019 Jun 10;:

Authors: Tsubokura M, Murakami M, Takebayashi Y, Nomura S, Ono K, Ozaki A, Sawano T, Kobashi Y, Oikawa T

Abstract
Following the Fukushima incident, doses from external exposure accounted for the majority of the total doses. Although countermeasures are being implemented aiming at reducing the radiation exposure, little information is available on the impact of decontamination on individual doses among the residents of radioactively contaminated areas. To evaluate the effectiveness of the decontamination measures in reducing individual doses and examine the influence of the timing of decontamination and the district, the data for 18,392 adults and 3,650 children in Minamisoma City, Fukushima, who participated in voluntary screening programs using individual radiation dosimeters (Glass Badge) between June 2013 and September 2016 were analyzed. The dose reduction rates (DRR) in 2013, 2014, and 2015 for one year were calculated and compared between in areas with and without decontamination. Using a regression approach and Monte-Carlo simulation, the dose reduction rate by decontamination (DRRd’) was also estimated. The annual DRR in areas with decontamination for both adults and children were significantly higher than those in areas without decontamination, depending on the timing of decontamination: 31-36% for 2013-2014 for adults in decontamination areas and 33-35% for children in decontamination areas compared to 12-23% and 13-23% for adults and children in areas without decontamination, respectively. There was a positive correlation between the DRRd’ and individual doses, and the DRRd’ was estimated 30-40% for adults and children with doses of 3 mSv/y in 2013 and 2014. This study demonstrated that the decontamination has an impact on lowering the individual doses from external exposure. The higher the dose at the time of starting the decontamination, the greater the dose reduction rate by decontamination, regardless of the timing of the decontamination. Our study confirms that decontamination was useful for high-dose areas in the later phases of the incident.

PMID: 31181542 [PubMed – as supplied by publisher]

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