Study of radon diffusion through clay bricks

Radon is a naturally occurring radioactive gas that is generated in the earth's crust and is free to migrate through soil and be released to the indoor and outdoor atmosphere. Much attention has been given to the radiological health hazard posed by increased radon concentrations in the living and working environment. In order to study radon profiles for geophysical purposes and to predict its entry indoors, it is necessary to study its transport through building materials. The most common way of modeling radon flow through building materials is the advective transport by pressure-driven air flow from the source. The transport phenomenon of radon through diffusion is a significant contributor to indoor radon entry. The diffusion coefficient of radon gas in building materials is often used as an indication for radon transportability through a porous medium and, furthermore, as an essential tool for quantitative predictions of radon concentrations in dwellings by estimating the exhalation rates of the wall surfaces. Radon diffusion coefficients in bricks were determined by employing the two compartment method in which one compartment is kept at a high radon concentration while the other is initially at low concentration. The radon diffusion coefficient is then deduced by monitoring the radon in the second compartment by measuring the steady state radon flux into the compartment. In this case, a steady-state solution was used to calculate the diffusion coefficient. The radon diffusion coefficients were found to vary from 0.32x10-6 m2/s to 0.48 x10-6 m2/s and the diffusion length were from 36x10-2 m to 42 x102 m in bricks. The results indicate that the bricks analyzed are fairly radon tight. (author)