Keywords:Fukushima Daiichi Nuclear Power Plant accident, reduction factor, in and around residential houses, temporal changes, former/current evacuation areas
In order to more appropriately estimate the exposure dose for residents in an existing exposure situation, it is important to evaluate air dose rates in residential houses where residents spend large portion of their time. For this purpose, it is necessary to use a proper value for reduction factor. Since 2012, we have been investigating the distribution of radioactive materials in and around residential houses for about 150 wooden houses within former/current evacuation areas, and evaluated reduction factor from the values around the houses. In this study, the dose reduction factors evaluated in 2012-2013 (before decontamination and immediately after decontamination) and those obtained in 2019 are compared, and the temporal change is reported.