Advantages of low-background liquid scintillation alpha-spectrometry and pulse shape analysis in measuring²²²Rn, uranium and²²⁶Ra in groundwater samples

Abstract

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 and²²⁶Ra contents in water and indicates the presence of some other long-lived radionuclides (²¹⁰Pb,²²⁸Ra or⁴⁰K). The LLD for U recorded with both spectrometers is 0.02 Bq⁻¹ and for²²⁶Ra 0.01 Bq·1⁻¹. The LLDs attained by this LSC method are two orders of magnitude lower than the maximum permissible concentrations set for U and²²⁶Ra.