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

就寝時の個人線量計着用/未着用時の線量指示値の違い

廣内 淳 ; 高原 省五 ; 渡邊 正敏*

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

福島第一原子力発電所事故後の住民の帰還に伴い、住民の線量は安全を醸成するために測定された。しかしながら、各住民の線量は同じエリアに住む住民でさえ、その振る舞いや居住環境によって異なる。従来の研究では、被験者は外出時には個人線量計を胸部に着用するように言われているが、室内では着用の必要が無かった。本研究では、就寝時に個人線量計を着用した場合と着用しなかった場合の線量指示値の違いを調査した。放射線量の高い2つの家屋において、成人ファントムの胸部上(着用時を模擬)、頭上付近(未着用時を模擬)に個人線量計を置き、その指示値を比較した。さらに、指示値の違いの原因を調査するため、放射線輸送計算を用いて就寝時の線量を計算した。結果として、着用時の線量は未着用時に比べて1階で約4%、2階で約15%低かった。さらに線量と線量比(未着用時/着用時)は窓からの距離に応じて、それぞれ約20%、約30%異なった。

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).