A simplified method of 85Kr measurement for dating young groundwaters

The technique of gas extraction from water and gas sample preparation for 85Kr low-level measurements was further developed to improve its applicability to isotope-hydrological "age" determinations of young groundwaters. A water sample of about 200 L is flushed with helium to extract the dissolved gases. Krypton is separated from the extracted gas mixture by repeated adsorption on charcoal, fractionated desorption and subsequent gas chromatography. The detection limit for a 10,000 min counting time in a 10 mL counter containing the krypton (15 microL) and methane as counting gas corresponds to 25 mBq 85Kr per mL (STP) krypton or 2.5% of the mean atmospheric 85Kr activity concentration in the year 1990.