Concentrations of Ra-226 and U-238 in soil samples from two Swedish es
kers were determined. One of the eskers, containing rock material from
a radioactive granite, revealed a high degree of radioactive disequil
ibrium between Ra-226 and U-238. The disequilibrium ratio was positive
ly correlated with particle size and soil permeability, indicating tha
t 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 th
e protective effect from the kerogen compounds in the alum shale is th
ought 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 mi
nerals or precipitated on the surface of the mineral particles. The pr
oportions 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.