Distributions of Thoron Progeny Concentrations in Dwellings

Abstract

The distribution of thoron (220Rn) and thoron progeny indoors was derived from the diffusion equation in two-dimensions. In the ordinary living environment, thoron concentration decreases exponentially with the distance from the wall. The activity of 216Po is almost in radioactive equilibrium with thoron due to the very short half-life of 216Po. Comparing the average concentration in the room, the number of attached 212Pb atoms is about seventy times larger than that of unattached 212Pb. The concentrations of 212Pb and 212Bi are spatially homogeneous. However, in the case of a small effective diffusion coefficient, a concentration distribution appears. In such a case, the absorbed dose from the thoron progeny could vary according to is proximity to the wall or the centre of the room. The general characteristics of thoron and its progeny concentration distribution indoors is presented.