Differences between radiation dose values under wearing and non-wearing geometries of personal dosimeters during sleep

Hirouchi, Jun ; Takahara, Shogo ; Watanabe, Masatoshi*

With the return of residents after the Fukushima Daiichi Nuclear Power Station accident, some residents' radiation doses have been measured to ensure their safety. However, personal radiation doses vary depending on the behavior and residential environment of each subject even for a group of subjects living in the same region at the same time. In past studies, subjects were required to wear a personal dosimeter on their chest outdoors, while they were not required to wear the device indoors. This study investigated the difference between the dose values indicated for the wearing and nonwearing conditions of personal dosimeters during sleep. In particular, an adult human phantom was used to compare the indicated dose values when personal dosimeters were placed on the chest (reproducing the wearing condition) and near the head (reproducing the nonwearing condition) in two houses with a high radiation dose. Furthermore, to understand the reason for the difference in the indicated dose values, the radiation dose during sleep was calculated using a radiation transport calculation code. The dose values for the wearing condition were approximately 4% lower on the first floor and approximately 15% lower on the second floor than those for the nonwearing condition. In addition, the radiation doses and radiation dose ratios (head/chest) differed by approximately 30% and 20%, respectively, depending on the distance from the nearest window (1-3 m).