The Geochemistry of Uranium and Thorium Isotopes in the Salt Lakes and Adjacent Ground Waters of Rajasthan

The concentrations of ²³⁸U, ²³⁴Th and (²³⁴U²³⁸U) activity ratios and major ion chemistry of several water samples from the salt lakes and their adjacent ground waters in Rajasthan have been measured. ²³⁴Th concentration in all the samples, except in one high alkalinity water from the Sambhar Lake, are quite deficient relative to its parent ²³⁸U the average (²³⁴Th/²³⁸U)activity ratio being 0.12. This deficiency corresponds to a mean residence time of - 5 days for ²³⁴Th in these waters. In the high alkalinity water, ²³⁴Th concentration is at near equilibrium with ²³⁸U, yielding a residence time much longer than radioactive mean life. The long residence time of Th in high alkalinity waters may result from the complexing of ²³⁴Th by (CO₃)^-2 ion. ²³⁸U concentration in some of the ground waters near the salt Iakes are high, the highest being in a Didwana sample, 565 dpm/l, The Didwana samples also have the highest (²³⁴U²³⁸U) activity ratios observed for Indian waters. The high uranium concentration in the Didwana ground water is suggestive of uranium rich aquifer solids.