Naturally occurring gamma-emitting isotopes, radon release and properties of parent materials of Saskatchewan soils

Abstract

Mineral composition of the parent material is a major factor controlling natural radioactivity of soils. The objective of this study was to investigate the relationship between the natural radioactivity of 18 till and six lacustrine parent materials and their properties measured during soil surveys. Gamma spectroscopy was used to estimate 40K and daughters of 238U and 232Th; neutron activation analysis was used to determine total U; and alpha counting was used to measure 222Rn release from the soil. The amounts of the various radioisotopes were positively correlated with each other and with clay content; the correlation with sand content was negative; and the correlations with silt and inorganic C content were generally not significant. Adding the fine/total clay ratio as a further independent variable considerably improved the correlation between 40K and clay content. The data suggested considerable disequilibrium in the 238U decay chain, which appeared to be in part related to the mode of deposition of the parent materials. Soil survey information — in particular, texture — thus appears a readily available tool for preliminary screening of terrestrial radiation in Saskatchewan. Key words: Radioactivity, 40K, uranium, thorium, radon, texture