The activity concentrations of ²³⁸U, ²³⁴U, ²³⁰Th, ²²⁶Ra,²³²Th, and ²²⁸Th in thermal spring waters in the Tatun volcanic area were determined. Parameters including acidity, Cl⁻ and SO₄²⁻ concentrations in spring waters at the sampling sites have been investigated to allow interpretation of the migration of the radionuclides, and to elucidate the influence of these parameters on the variations of radionuclide contents. Radioactive disequilibria were found in uranium and thorium series in thermal spring waters. The contents of uranium and thorium decreased with increasing pH. The ratios of ²³⁰Th/²³⁴U, ²²⁶Ra/²³⁰Th and ²²⁸Th/²³²Th show significant disequilibria. The ²²⁶Ra/²³⁰Th ratio (0.60-34.8) decreased with the Cl⁻or SO₄²⁻ concentration. All ²²⁸Th/²³²Th ratios (1.01-9.49) deviated from unity due to the co-precipitation of ²²⁸Ra with barium and lead sulfate.
