福島県木造家屋内外の空間線量率の分布調査

Dose reduction factors of Japanese houses are important for estimating the levels of external exposure of returning residents. In 2019, a total of 19 wooden houses were surveyed in Iitate Village and Namie Town using a gamma plotter that can continuously measure the air dose rate, with six houses selected for analysis. The characteristics of the dose reduction factor were investigated from the measured air dose rates in and around each house. In the vicinity of a house, uncontaminated land exists beneath the structure, and paved surfaces such as asphalt roads occupy a high fraction of the land around the structure. In pavements, the radiation source tends to be washed away rapidly. Therefore, the air dose rate near each house was relatively low. Within a radius of 50 m from the center of a house, air dose rates above unpaved surfaces were higher and had larger variations than those above paved surfaces. The dose reduction factor was widely distributed even for one house when the ratio of the air dose rates observed inside and outside the building was considered. It is thus suggested that a representative reduction factor may not be obtained if it is based on a small number of measurements that do not capture the full variation of the radiation field around a house.