A modified accumulator method for measuring surface radon flux from a uranium tailings pile

A modified accumulator was devised to measure surface radon flux from porous media. It consists of a collector hood accumulator with a homogenizer pump and a pressure balancer. The latter was used to compensate for any pressure changes produced during sample withdrawl and hence eliminate additional radon transport from media. Errors resulting from radon back diffusion due to decreasing concentration gradient with time across the interface were eliminated by measuring radon concentrations in the accumulator for two different periods of time and calculating the true radon flux, J(o), from the solution of a time-dependent radon transport equation. Core samples from the observation site were withdrawn for laboratory determination of pkrosity, moisture content, bulk and grain densities, Ra-226 source concentration and the fraction of Rn-222 produced in the void volume. The data were used to calculate the radon diffusion coefficient for the media. Using the present method, the true value of surface radon flux for an abandoned uranium tailings pile was found to be J(o) = 2020.2 mBq/m2/sec compared to the value J = 1406.0 mBq/m2/sec kbtained by the conventional method. The bulk diffusion coefficient of radon for the medium was obtained as 1.2 x 10-7 m2/sec