Individual external doses and conversion coefficients for outdoor workers after the lifting of evacuation orders in specified reconstruction and revitalization base areas following the Fukushima Daiichi nuclear power station accident

Saisu, Motofumi*; Ochi, Kotaro  ; Uchiyama, Keizo*; Mizuno, Naruhito*; Yoshida, Masashi*; Sanada, Yukihisa   

After evacuation orders were lifted in Specified Reconstruction and Revitalization Base Areas following the Fukushima Daiichi accident, individual external doses of outdoor workers were measured using personal dosimeters and compared with airborne-derived ambient dose rates. Median hourly doses after lifting were significantly lower than before. The median conversion coefficient from ambient to individual dose was 0.39, below the commonly used value of 0.6, but consistent with previous results. These findings indicate that current government models provide conservative dose estimates and that conversion coefficients remain stable under post-evacuation conditions.