ABSTRACT

Deviations from the natural isotopic composition of the ²³⁴U/²³⁸U and ²²⁸Th/²³²Th activity ratios have been determined for nine different hot spring water samples from Venezuela. The ²³⁴U/²³⁸U activity ratios range from 1.13 ± 0.07Ci/Ci to 9.94 ± 2.53 Ci/Ci in the samples Quebrada la Colonia and Aguas Calientes Ure=a, respectively. The ²²⁸Th/²³²Th activity ratios range from 3.20 ± 0.25 Ci/Ci to 21.60 ± 1.81 Ci/Ci in the Quebrada la Colonia and Las Trincheras hot spring samples. A linear relationship was found between ²²⁸Th/²³²Th activity ratio and the amount of dissolved SiO₂ in mg/l which follows the relationship ²²⁸Th/²³²Th=0.2397 SiO₂ + 0.5402. The wide deviations in the activity ratios measured were attributed to mechanisms of differential solubility of the intermediate short lived daughters in the decay chain of uranium and thorium (²³⁴Th, ²³⁴Pa, ²²⁹Ra, ²²⁸Ac) and to the effect of recoil of the decaying nuclei during alpha and beta emissions.