Summary of temporal changes in air dose rates and radionuclide deposition densities in the 80 km zone over five years after the Fukushima Nuclear Power Plant accident

Saito, Kimiaki  ; Mikami, Satoshi   ; Ando, Masaki  ; Matsuda, Norihiro  ; Kinase, Sakae   ; Tsuda, Shuichi  ; Yoshida, Tadayoshi ; Sato, Tetsuro*; Seki, Akiyuki   ; Yamamoto, Hideaki*; Sanada, Yukihisa   ; Wainwright-Murakami, Haruko*; Takemiya, Hiroshi

We summarized temporal changes in air dose rates and radionuclide deposition densities over five years in the 80 km zone based on large-scale environmental monitoring data obtained continuously after the Fukushima Nuclear Power Plant (NPP) accident. The air dose rates in environments associated with human lives decreased at a considerably faster rate than expected for radioactive decay. The average air dose rate originating from the radiocesium deposited in the 80 km zone was lower than that predicted from radioactive decay by a factor of 2-3 at five years after the accident. The causes of this rapid reduction were discussed quantitatively considering the characteristics of radiocesium migration in the environment.