Radioactive disequilibrium of uranium and actinium series nuclides in soil

Author:
  • KMKazuko Megumi
    Kazuko Megumi
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Abstract
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.

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