Determination of 238U in ground-water samples using gamma-ray spectrometry

A method for measuring the low activity concentration of 238U in water is described. Samples of 50 L were evaporated and the dry residue after evaporation was measured. Typically, 30 g of material was obtained for the samples processed in this way. Based on measuring the samples using a gamma-ray spectrometer, equipped with a germanium crystal having a diameter of 8 cm and a beryllium window, the decision threshold resulting from the measurements was assessed to be 1.5 Bq/m3. A total of 26 samples of ground water were processed and activity concentrations of up to 20 Bq/m3 were measured. However, most of the results were in a range around 5 Bq/m3.