Projections of future ambient dose rates in a mountainous area in the Fukushima evacuation zone, Japan

Abstract We measured ambient dose rates in a mountainous area in the evacuation zone (Namie town, Fukushima prefecture, Japan) to predict ambient dose rates several decades ahead based on collected data. The survey was conducted on a ridge in a mountainous area that had not been previously decontaminated. Future ambient dose rate projections based on observed dose rates suggest a faster dose rate decline than those based on the physical decay of radiocesium. Specifically, the projections based on observed data indicate that the Japanese decontamination threshold in the area would be reached 15 years earlier than predicted based on physical decay.