Temporal change in radiological environments for five years after the Fukushima accident

福島事故後5年間における放射線環境の経時変化

斎藤 公明  

Saito, Kimiaki

Temporal change in radiological environments for five years after the Fukushima accident has been clarified on the basis of the large-scale environmental measurements repeatedly carried. Air dose rates in living environments have decreased much faster than the physical decay. A prediction model for air dose rate distribution has been developed according to statistical analyses of accumulated massive car-borne survey data. In June 2011 plural radionuclides were detected; while, radiocesium was found to be far more important than other radionuclides from a viewpoint of long-term exposure. The movement of radiocesium in horizontal directions in natural fields is generally slow, but radiocesium deposited on ground has gradually penetrated into deeper parts. The results obtained in the projects have been applied to different kinds of extensive analyses. Significant exposure doses to inhabitants have not been reported so far though further investigation is necessary.