The theory and uses of natural uranium isotopic variations in hydrology

The dissolved concentration of uranium and the relative abundance of two uranium isotopes, **2**3**4U and **2**3**8U, vary over a wide range of values in natural waters. The concentration is controlled mainly by the redox potential of the environment and by CO//2. The mechanism of isotope fractionation is thought to be entrainment of **2**3**4U in the aqueous phase either by selective leaching of the solid phase or by direct recoil of the daughter nuclide. Ion exchange techniques and alpha-spectrometery permit the measurement of uranium at concentrations as low as pp 10**1**1 and the isotopic ratio to a few per cent. In oxidizing conditions the uranium isotopes behave in a chemically stable conservative manner such that separate groundwater sources may have identifiably different characteristics and mixing volume calculations may be made. Other potential uses of these isotopes include radiometric dating, tracing of hydrologic systems, ore prospecting and earthquake prediction.