A RAPID METHOD FOR MONITORING OF URANIUM AND RADIUM IN DRINKING-WATER

A time-saving and fairly accurate method for monitoring U and Ra-226 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(TM), 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 Ra-226 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, Ra-226, Pb-210 and Po-210 activities, and on the U-234:U-238 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 Ra-226 levels in drinking water. The lower limits of detection for U and Ra-226 are 0.02 and 0.01 Bq/1, respectively, when the counting time is 180 min and the sample volume 38 ml.