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 w aters 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 Ra-226 and uranium (total) acti vities in natural water samples, Sample preparation involved filtratio n and 1:10 concentration by evaporation, Then, 8 mi of the sample were mixed with 12 mi of OptiPhase Hisafe 3 scintillation cocktail in lon- diffusion vials. These were stored for 1 month before counting in orde r 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 Ra-226 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.