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Following the Fukushima incident, radiation doses from external exposure accounted for the majority of the total doses. Although countermeasures are being implemented, with the aim of reducing radiation exposure, little information is available on the effects 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 to examine the influence of the timing of decontamination and the district, data were analysed for 18 392 adults and 3 650 children in Minamisoma City, Fukushima, who participated in a voluntary screening programme using individual radiation dosimeters (Glass Badge) between June 2013 and September 2016. The dose reduction rates (DRR) were calculated for one year by comparing the first and last three-month measurement results between areas with and without decontamination. Using a regression approach and Monte Carlo simulation, the dose reduction rate by decontamination eliminating the effect of physical decay (DRRd′) was also estimated as a function of the timing of the decontamination and the dose at the time of starting the decontamination. 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 2013–14 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 DRRd′ and individual doses, and DRRd′ was estimated at 30%–40% for adults and children with doses of 3 mSv y−1 in 2013 and 2014. This study demonstrated that decontamination does lower 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. [ABSTRACT FROM AUTHOR]

After the Fukushima disaster in 2011, affected residents experienced increased radiation-related anxiety and reduced subjective wellbeing. We investigated whether reduction of radiation-related anxiety promoted wellbeing among evacuees in Fukushima and assessed the role of mental health distress as a mediator. We used data from questionnaire surveys of evacuees in the 2011 and 2012 fiscal years (N = 34 312). We used radiation risk perception as an indicator of radiation-related anxiety and the frequency of laughter as an indicator of wellbeing. We measured changes in radiation risk perception from 2011 and 2012, and the frequencies of laughter and mental health distress (Kessler 6-item scale) in 2012, and investigated associations between radiation risk perception and frequency of laughter with and without covariates of mental health distress. Perceived genetic risk in 2011 had a significant inverse association with the frequency of laughter. Lowering of radiation risk perception was significantly associated with the frequency of laughter in the absence of covariates of mental health distress, but not in their presence. Lowering of radiation risk perception was also significantly associated with low mental health distress. Reduction of radiation-related anxiety promoted wellbeing via alleviation of mental health distress. [ABSTRACT FROM AUTHOR]