A rapid method for monitoring of uranium and radium in drinking water

A time-saving and fairly accurate method for monitoring U and 226Ra in drinking water has been devised, using low-background liquid scintillation spectrometry and pulse-shape analysis. The samples are prepared for counting by evaporating water in a liquid scintillation vial. The residue is dissolved in 1 ml of 0.5 N HCl, and a scintillation cocktail is added. Counting is carried out twice: a few days and a month after the sample preparation using the Quantulus, a liquid scintillation spectrometer equipped with a guard counter and pulse-shape analyser. The counter produces separate alpha and beta spectra which enable calculation of the approximate U and 226Ra contents. These correlate well with the results obtained by radiochemical methods. The measured spectra give valuable information on the nuclide content, e.g. increased U, 226Ra, 210Pb and 210Po activities, and on the 234U: 238U activity ratio in the water. This kind of information is very valuable in deciding on the necessity for time-consuming radiochemical analyses for radiation protection purposes or exploration for U ore deposits. In many cases the results from the Quantulus are sufficient to determine the U and 226Ra levels in drinking water. The lower limits of detection for U and 226Ra are 0.02 and 0.01 Bq/l, respectively, when the counting time is 180 min and the sample volume 38 ml.