Simulation of thoron and thoron progeny concentrations in the indoor environment

Thoron (Rn-220) exhalation from building materials has become increasingly recognized as a potential source for radiation exposure in domestic houses. However, contrary to radon (Rn-222), little is known about the exposure to thoron and its short-lived decay products. The purpose of this study is to estimate the concentration of thoron and its progeny products in a typical Dutch living room using computational fluid dynamics. The predicted thoron concentration is approximately 9 Bq m(-3) using a best possible estimate of 14 Bq s(-1) for the thoron exhalation from building materials. The concentration varies from 15 Bq m(-3) near the building materials to 2.7 Bq m(-3) in the center of the living room. The predicted concentrations of thoron's decay products Pb-212 and Bi-212 are 0.35 and 0.11 Bq m(-3), respectively. The thoron exhalation is derived theoretically and is based on measured radon exhalation rates of the most commonly used building materials in the Netherlands.