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 l21 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.