Movement of radon in overburden

An analytical solution for simple one-dimensional geometry establishes the basic theory of the movement of ²²² Rn (radon) in overburden, involving diffusion and convection. The computer-adapted finite-difference method is then used to determine radon concentrations for the following more complex configurations: a two-dimensional source, a vertical fault, a three-dimensional source, and multilayered overburden. The key parameters are the radon concentration at the source, the diffusion coefficient of the overburden, and the geometry. This analysis indicates that if diffusion is the only transport process considered, the maximum depth at which uranium mineralization can be detected by the usual types of field equipment is limited to a few tens of meters. However, if convective transfer is also considered, radon attenuation is significantly decreased, e.g., by as much as a factor of 800 for a one-dimensional configuration considered. It appears that an upward velocity component for the movement of radon, or geochemical dispersion of uranium and radium, are needed for long-distance detection of uranium mineralization.