A theoretical approach to the measurement of radon diffusion and adsorption coefficients in radonproof membranes

Theoretical expressions for the determination of radon diffusion and adsorption coefficients in radonproof membranes using the standard method for testing the radon insulation effectiveness of a membrane tightly placed between two compartments are derived from the steady-state solution of the differential equation for radon diffusion. These expressions are applied to an experimental set-up designed specifically to carry out such a determination under controlled environmental conditions. Minimum detectable radon diffusion and adsorption coefficients of the method are shown to be typically well below those measured in most of the materials commonly used as radon barriers. Besides the radon diffusion and adsorption coefficients a new parameter called radon flux transmission factor and a more suitable definition of the radon permeability coefficient are also proposed to characterize the applicability of any membrane for radon insulation purposes