Rapid processing of 85Kr/Kr ratios using Atom Trap Trace Analysis

We report a methodology for measuring Kr-85/Kr isotopic abundances using Atom Trap Trace Analysis (ATTA) that increases sample measurement throughput by over an order of magnitude to six samples per 24 h. The noble gas isotope Kr-85 (half-life=10.7 years) is a useful tracer for young groundwater in the age range of 5-50 years. ATTA, an efficient and selective laser-based atom counting method, has recently been applied to Kr-85/Kr isotopic abundance measurements, requiring 5-10 L of krypton gas at STP extracted from 50 to 100 L of water. Previously, a single such measurement required 48 h. Our new method demonstrates that we can measure Kr-85/Kr ratios with 3-5% relative uncertainty every 4 h, on average, with the same sample requirements.