Monte Carlo simulation of indoor external exposure due to gamma-emitting radionuclides in building materials

The use of building materials containing naturally occurring radionuclides, such as ⁴⁰K, ²³⁸U, ²³²Th and their progeny, could lead to external exposures to the residents of such buildings. In this paper, a set of models are constructed to calculate the specific effective dose rates (the effective dose rate per Bq/kg of ⁴⁰K, the ²³⁸U series, and the ²³²Th series) imposed on residents by building materials with the MCNPX code. The effect of chemical composition, position concerned in the room and thickness as well as density of material is analyzed. In order to facilitate more precise assessment of indoor external dose due to gamma-emitting radionuclides in building materials, three regressive expressions are proposed and validated by measured data to calculate specific effective rates for ⁴⁰K, the ²³⁸U series and the ²³²Th series, respectively. (authors)