Methods for measuring diffusion coefficients of radon in building materials

Two methods for determining the Rn-222 diffusion coefficient in concrete are presented. Experimentally, the flush and adsorption technique to measure radon release rates underlines both methods. Theoretically, the first method was developed fur samples of cubical geometry. The radon diffusion equation was solved for boundary conditions imposing zero flux conditions successively on each side. In practice, a 100% effective covering would ensure this condition to be satisfied. The diffusion coefficient is then determined by comparing the computed and respectively measured normalized ratios of the radon release rates with respect to the rate corresponding to the open-boundaries (uncovered) specimen. As in practice, none of the investigated coverings showed to be effective in reducing radon exhalation, indicating that radon-tight sealing of surfaces is far from trivial, no clear conclusions could be drawn with respect to the diffusion coefficient. The second method can be applied to specimens that are first reshaped into hollow cylinders. A one-dimensional situation can be inforced by requiring that the flux vanishes at the two ends of the hollow cylinder. The theoretical and experimental ratios are again compared. In practice, the radon flux originates from a radon source enclosed inside the hollow cylinder, the effectiveness of the sealing being previously tested on an aluminum dummy of similar dimensions. The radon bulk diffusion coefficient for the used concrete sample resulted in a value of D = (4.6 +/- 0.4) x 10(-6) cm(2) s(-1). (C) 2001 Elsevier Science B.V. All rights reserved.