An improved method for 85Kr analysis by liquid scintillation counting and its application to atmospheric 85Kr determination

Atmospheric (85)Kr concentration at Fukuoka, Japan was determined by an improved (85)Kr analytical method using liquid scintillation counting (LSC). An average value of 1.54 +/- 0.05 Bq m(-3) was observed in 2008, which is about two times that measured in 1981 at Fukuoka, indicating a 29 mBq y(-1) rate of increase as an average for these 27 years. The analytical method developed involves collecting Kr from air using activated charcoal at liquid N(2) temperature and purifying it using He at dry ice temperature, followed by Kr separation by gas chromatography. An overall Kr recovery of 76.4 +/- 8.1% was achieved when Kr was analyzed in 500-1000 l of air. The Kr isolated by gas chromatography was collected on silica gel in a quartz glass vial cooled to liquid N(2) temperature and the activity of (85)Kr was measured with a low-background LS counter. The detection limit of (85)Kr activity by the present analytical method is 0.0015 Bq at a 95% confidence level, including all propagation errors, which is equivalent with (85)Kr in 1.3 l of the present air under the analytical conditions of 72.1% counting efficiency, 0.1597 cps background count rate, and 76.4% Kr recovery.