The activities of natural radionuclides,
238U,
234U,
226Ra,
228Ra,
222Rn,
210Pb and
210Po in ground waters collected from Okinawa Island were measured. The
234U/
238U activity ratios in most samples showed more or less unity, whereas, relatively high values of 2.0-4.0 were obtained in samples from Motobu area.
222Rn activities in the ground waters were much higher than the other uranium series nuclides. The
222Rn/
226Ra activity ratios ranged from 3000 to 29000, and those for
210Po/
210Pb were from 0.08 to 0.82. On the whole, activities of the nuclides in the ground waters at the studied points showed higher in the order of
222Rn≫
210Pb>
234U>
238U>
226Ra>
210Po. In addition to α_recoil dissolution, the selective absorption and/or desorption by some organic or inorganic substances in the aquifer may be happening.
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