Concentrations of Uranium Series Nuclides in Soil Particles in Relation to Their Size

Basic Information for Monitoring of Radioactive Contamination in Soil

Abstract

In order to study the behaviors of uranium series nuclides in soil, a soil sample, which was derived from weathering of granite rock, was separated into several particle size ranges, and each of the separated fractions was analyzed for the concentrations of ²³⁸U, ²³⁰Th, ²²⁶Ra and ²¹⁰Pb by means of γ-ray spectrometry with Ge(Li) detectors. The activity ratios of ²³⁰Th/²³⁸U, ²²⁶Ra/²³⁸U and ²¹⁰Pb/²³⁸U were found to be larger than unity for all the size ranges; the ratio of ²³⁰Th/²³⁸U was especially high, reaching 3 to 5. It was further found that in a size range smaller than 0.15mm the concentrations of the four nuclides increased with decrease in particle size. It is pointed out that the size of soil particles as well as the disequilibrium between the uranium series nuclides can be important factors which should be taken into consideration when monitoring of radioactive contamination in soil.