ENHANCEMENT OF U-234 IN SPRINGWATERS OF AGUAS-DA-PRATA, SAO-PAULO, BRAZIL

Springwater samples were collected at Aguas da Prata, an important spa in São Paulo State, Brazil. The U-238 and U-234 isotopes were evaluated for Platina, Paiol, Villela, Prata-Radioativa, Prata-Nova, Boi, Vitoria, and Prata-Antiga springs. An inverse logarithmic correlation was found between U-234/U-238 activity ratio and Rn-222 content of the studied waters, which was related to different solution mechanisms of Rn-222 and U-234 nuclides at the rock-water interface. A linear correlation also exists between the U-234/U-238 activity ratios of the studied waters and total dissolved solids, ionic strength, CO2 partial pressure, and index of base exchange, which indicates that the enhancement of U-234 in solution increases with the degree of weathering in the aquifers, A higher U-234/U-238 activity ratio was found to be directly related to a higher value of dissolution rate.

The transfer of uranium isotopes U-234 and U-238 to the waters interacting with carbonates from Mendip Hills area (England)

Laboratory time-scale experiments were conducted on limestone and dolomite gravels from the Mendip Hills area, England, with the purpose of evaluating the release of U-238 and U-234 to different aqueous solutions. The U-234/U-238 activity ratio (AR) lab data were reliable to interpret the field data. The obtained values do not indicate a reduction in the amount of dissolved U and an increase in the AR of the remaining dissolved U as commonly observed for groundwater systems close to redox boundaries. (C) 2000 Elsevier B.V. Ltd. All rights reserved.