Advantages of low-background liquid scintillation alpha-spectrometry and pulse shape analysis in measuring 222Rn, uranium and 226Ra in groundwater samples

Liquid scintillation counting (LSC) and pulse shape analysis (PSA) was used in measuring radon and gross alpha-and beta-activities in groundwater. We used conventional LSC counters for the measurement of radon in water, but low-background LSC spectrometers for the gross activity measurements. The lower limit of detection (LLD) for radon in water is 0.6 Bq/l for a 60 min count with a conventional counter, but 0.1 or 0.2 Bq/l, with the two types of low-background LSC spectrometers equipped with a pulse shape analyser (PSA). The gross alpha and beta activity measurements are made using a simple sample preparation method, PSA of a low background LSC and spectrum analysis. The LLD recorded for gross alpha and beta with the two spectrometers are 0.02 and 0.03 Bq/l and 0.2 and 0.4 Bq/l, respectively, for a 180 minutes count and a 38 ml sample volume. The method also enable the calculation of the U and (226)Ra contents in water and indicates the presence of some other long-lived radionuclides, ((210)Pb, (228)Ra or (40)K). The LLD for U recorded with both spectrometers is 0.02 Bq(-1) and for (226)Ra 0.01 Bq.l(-1). The LLDs attained by this LSC method are two orders of magnitude lower than the maximum permissible concentrations set for U and (226)Ra.