[1M05-12] Environmental Radioactivity 1

[1M12] Investigation on distribution of radioactive substances in Fukushima

(6)Temporal changes in reduction rates of air dose rate in and around residential houses within former evacuation areas

*Hiroko Yoshida¹, Masateru Hayashi², Taisuke Makita², Tetsushi Azuma², Makoto Sasano², Shuichi Tsuda³ (1. Tohoku Univ., 2. Mitsubishi Electric, 3. JAEA)

Keywords:Fukushima Daiichi Nuclear Power Plant accident, air dose rate, temporal changes, in and around residential houses

Since 2012, we have been continuously measuring air dose rates in and around residential houses withinformer and current evacuation areas. Reduction rates of air dose rates from before decontamination to immediately after decontamination, and from before decontamination to 2019/2020 for 54 houses in Iitate Village and Odaka District, Minamisoma City, were compared for outdoors and indoors, respectively. The largest reduction rate in air dose rates was observed outdoors immediately after decontamination (median:58.4%), and the smallest indoors immediately after decontamination (median: 43.3%), indicating a clear difference between the two. However, in the evaluations for 2019/2020, the reduction rates of outdoor air dose rates increased, and the median value of reduction rates in both outdoor and indoor air dose rates was almost 50%, indicating that there was no difference between the two. In this presentation, we will report the results of our study of its trends and causes.