A new methodology for the evaluation of radon diffusion coefficients in anti-radon membranes

Indoor radon is classified as a carcinogen because it can lead to lung cancer. Some radon preventive strategies are related to building protection with radon barrier materials whose capacity to stop the gas depends on the diffusion coefficient, which can be calculated using different techniques. In this article, we propose a new experimental device, called TESTMAT, to measure the radon diffusion coefficient, using a weak radon source, to prevent radiation protection oversight. The device is small and made from PVC. The sample of the tested material is placed between the source and the receiver containers, as indicated by ISO/TS 11665-13 standard. Since a non-stationary radon diffusion occurs in the system, we developed a specific software, ENDORSE, to model radon activity concentrations in the receiver chamber and the diffusion through the material by applying the explicit finite difference method. The software utilizes Montecarlo simulation to determine the error associated with the diffusion coefficient. Different tests were performed to calibrate the system and assess the value and the evolution of background radon during the two-week measurement. When working with low-activity radon sources, this parameter cannot be neglected, particularly with the best performing membranes. An adequate sample holder was selected to guarantee a good airtightness, with a leakage constant of only 7 % of the radon decay constant. The minimum detection limits were calculated based on the material thickness and the source intensity. The system was finally tested with three commercially available waterproofing membranes and results compared with expected values, based on literature.