Alpha radiometry of uranium in surface and ground waters by liquid scintillation counting after separation of the radionuclide by cation exchange

Abstract

The alpha radioactivity of surface and ground water samples has been determined by liquid scintillation counting (LSC) after chemical preparation of the samples by cation exchange using the Chelex 100 resin. The method applied to certain natural waters is selective for uranium and the alpha radioactivity measured corresponds primarily to the uranium radioactivity in those systems. Method calibration using uranium standard solutions results in a detector efficiency of ( 97 ± 2 ) % and in a cation exchange separation efficiency of ( 85 ± 6 ) % . Application of the method to laboratory solutions of constant uranium concentration and variable composition (0.1, 0.5 and 1 M NaCl; 0.1 and 0.5 M Ca ( NO 3 ) 2 ; 0.1 and 1 mM FeCl 3 ; 10 and 100 ppm SiO 2 ; 10 and 100 ppm humic acid) shows generally that the cation exchange efficiency is not significantly affected by the presence of major components, except for increased Fe(III) concentrations in a solution ( > 0.1 mM ) . Radiometric analysis of local (Cypriot) natural waters showed that uranium concentration in ground waters varies strongly (1600–90 mBql - 1 ) depending on the hosting geological matrix, whereas surface waters contain relatively low uranium (40–110 mBql - 1 ) resulting in values for alpha radioactivity close to the detection limits of the method (30 mBql - 1 ).