Radioactive disequilibrium of uranium and actinium series nuclides in soil

The concentration of uranium series nuclides (238U, 234U, 230Th, 226Ra, and 210Pb) and actinium series nuclides (235U and 227Ac) were determined by γ ray spectrometry for size-separated soil samples collected in Murho and originating from the weathering of granite rock. Each activity ratio of a descendant to 238U or 235U is found to be larger than unity. Extraction tests show that approximately 50% of the uranium series nuclides reside on the surface of soil particles and approximately 80% of the 230Th is surface correlated. Because of the anomalously high radioactivity levels, it was possible to obtain sufficient data to estimate the age of weathering of the soil. A weathering age of >103 years was estimated from the 230Th and 226Ra surface-correlated activities