Concentration of uranium series nuclides in soil particles in relation to their size

Soil was separated according to particle size, and the concentrations of the uranium series nuclides 238U, 230Th, 226Ra, and 210Pb in each size-separated fraction were determined by γ ray spectrometry with Ge(Li) detectors. The activity ratios of 230Th, 226Ra, and 210Pb to 238U were larger than unity in all fractions. The activity ratio of 230Th to 238U was unexpectedly high, reaching 3--5. In the particle size range below 0.1 mm the concentrations of these uranium series nuclides were found to increase with decrease in particle size. Such a trend was also found for the elements Fe, Mn, Zn, and Cu. The elements K and Ca, however, were found to have a direct correlation with particle size