1977 年 12 巻 3 号 p. 181-186
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.