Water-rock interactions, radioactive

While it is expected that the source rocks for the radionuclides of interest in many environments were deposited more than a million years ago and that the isotopes of uranium would be in a state of radioactive equilibrium, physical fractionation of " U from U during water-rock interaction results in disequilibrium conditions in the fluid phase. This is a result of (1) preferential leaching of " U from damaged sites of the crystal lattice upon alpha decay of U, (2) oxidation of insoluble tetravalent " U to soluble hexavalent " U during alpha decay, and (3) alpha recoil of " Th (and its daughter " U) into the solute phase. If initial ( " U/ U).4 in the waters can be reasonably estimated a priori, the following relationship can be used to establish the time T since deposition,... 

Ar. With its half-life of 269 yr, Ar covers a very important age range between the ranges accessible by H- He, Kr, CFCs and Sp6 (younger than 50 yr) and by (older than about 1 kyr). It also has quite ideal properties, similar to those of Kr, with the exception that subsurface production cannot a priori be neglected and may in some cases lead to deviations of the evolution of the Ar concentration from the pure radioactive decay. In crystalline rocks, dating may even be impossible, but Ar may then be used to study water-rock interactions (Loosli et al. 1989 Loosli et al. 1992). As for Kr, the reason why Ar has not been applied more widely lies in the difficulty of its analysis. 

Eikenberg, j. Lichtner, P. C. 1992. Propagation of hyperalkaline cement pore waters into the geologic barrier surrounding a radioactive waste repository. In Kharaka, Y. K. Maest, A. S. (eds) Water-Rock Interaction. Balkema, Rotterdam, 377-380. 

For the low energy electrons produced by solar neutrino interactions, there are backgrounds arising from natural radioactivity, primarily radon dissolved in the detector water, from gamma-rays emitted by radioactive elements in the rock of the cavity housing the detector, and from the beta-decays of the muon-induced spallation nuclei in the water. 

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