Concentration of natural radioactive nuclides and mineral compositions in soil in relation to their sizes

Each soil sample of more than 10 kg (dry weight) was collected on three sites in southern part of Seta in Shiga prefecture and was separated into seven particle sizes. Each sieved soil sample was analyzed for the mineral compositions by means of X-ray diffraction and the concentrations of 238U, 226Ra, 228Ra and 40K by means of γ-ray spectrometry with Ge(Li) detectors. There were trends for the contents of anorthite (calcium-rich feldspar) decrease rapidly and those of albite (sodium-rich feldspar) and quartz to decrease slowly as particle size decreased. It is found that the concentrations of 238U, 226Ra, 210Pb and 228Ra increase with decreasing particle size and that of 40K decreases with decreasing particle size. It is concluded that for the soil weathered from a mother's rock the concentrations of 238U, 226Ra, 210Pb and 228Ra decrease with increasing the concentrations of 40K. (author)