Measurements of gamma dose rates in dwellings in the Tokyo metropolitan area

Absorbed dose rates in air due to natural gamma rays were measured in 246 dwellings in the Tokyo Metropolitan area using thermoluminescence dosemeters. The mean absorbed dose rates in air were 53.7, 38.6 and 32.5 nGy.h-1 for concrete, wood frame and lightweight steel frame dwellings, respectively. It was found that these indoor radiation levels are high in comparison with the original radiation levels on uncovered ground particular to the geological features. This would be considered due to the urbanisation of the environment. For wood frame houses, an obvious difference was found in dose rates due to the building materials in walls, ceilings and floors. There was no significant difference in dose rates due to geological features in this area. (Author)