Radium and uranium concentrations in two eskers with enhanced radon emission

Concentrations of Ra-226 and U-238 in soil samples from two Swedish eskers were determined. One of the eskers, containing rock material from a radioactive granite, revealed a high degree of radioactive disequilibrium between Ra-226 and U-238. The disequilibrium ratio was positively correlated with particle size and soil permeability, indicating that a major part of the Ra-226 is adsorbed on the surface of the mineral particles. The other esker, with uraniferous alum shale material and carboniferous slates, revealed a much lower degree of disequilibrium, indicating that a major part of the Ra-226 is bound to primary uranium minerals. A less intense weathering of the uranium minerals due to the protective effect from the kerogen compounds in the alum shale is thought to be the main reason for this. The results indicate that Ra-226 may be present in a weathered soil in two ways: in primary uranium minerals or precipitated on the surface of the mineral particles. The proportions may vary depending on the type of rock material, weathering conditions, and permeability of the soil. This is of great importance to the process of radon emanation, since it is much higher from radium that is adsorbed on the surface of soil particles compared to radium bound in primary uranium minerals. Copyright (C) 1996 Elsevier Science Ltd.