Simultaneous determination of radium and uranium activities in natural water samples using liquid scintillation counting

The determination of radium and/or uranium concentrations in natural waters is useful in a wide range of environmental studies. In this work, a low-background liquid scintillation system (Wallac, Quantulus 1220) was used to determine simultaneously 226Ra and uranium (total) activities in natural water samples. Sample preparation involved filtration and 1:10 concentration by evaporation. Then, 8 ml of the sample were mixed with 12 ml of OptiPhase Hisafe 3 scintillation cocktail in low-diffusion vials. These were stored for 1 month before counting in order to ensure secular equilibrium between radium and its daughters. For a counting time of only 360 min, the detection limits achieved were 0.014 and 0.033 Bq l-1 for 226Ra and uranium, respectively. In order to test the method, several Ebro river water samples were analysed by both liquid scintillation and a sensitive fluorimetric technique.