Determination of the radon surface emanation rate from laboratory emanation data

Abstract

Indoor radon concentration depends on many factors, one of the most important of which is the surface emanation rate of house construction materials. The surface emanation rate of radon in an existing building may be calculated from indoor radon concentration measurements, provided that parameters such as the air exchange rate are known. However, it is important to be able to determine the surface emanation rate from laboratory measurements in order to preselect materials for building purposes. Laboratory data usually yield the mass emanation rate (Bq kg −1h −1) or the emanation coefficient of the investigated material, while for application purposes, knowledge of surface emanation rate (Bq m −2 h −1) is more important. Surface emanation rate cannot be calculated from mass emanation rate simply from the dimensions of the material. The purpose of the present work is to define the best means of relating laboratory emanation data to the surface emanation rate of radon. It is shown here that the surface emanation rate, E s, may be correlated with the mass emanation rate, E rmm , by the relation E s = E m pd or E s = E m pL where p is the density of the material, L the radon diffusion length in the material, and d the half-thickness of the material. Factors which may affect the theoretically calculated surface emanation rate are discussed.