A New Radiokrypton Dating Facility at Argonne National Laboratory

Due to its simple production and transport in the terrestrial environment, 81Kr (half-life = 230,000 yr) is an ideal tracer for old water and ice with mean residence times in the range of 105-106 years. Likewise, the anthropogenic isotope 85Kr (half-life = 10.8 yr) is a valuable tracer of young groundwater. In recent years, Atom Trap Trace Analysis (ATTA) of both isotopes has been made available to the earth science community thanks to significant advances in the ATTA technique developed at Argonne National Laboratory (ANL). ATTA is a laser-based atom counting method that is both efficient and isotopically selective. The 3rd generation ATTA instrument at ANL has measured Kr isotope ratios in over 250 environmental samples across all seven continents and can currently handle samples as small as 1µL of Kr gas (STP), which can be extracted from 10 L of water or 5 kg of ice. We are now developing a second ATTA instrument at ANL for a new radiokrypton dating facility to be used exclusively for environmental samples. Recent improvements to the ATTA method allow this facility to measure up to 250 81Kr or 1500 85Kr samples per year. It will also include a dedicated gas purification system for separating krypton from the degassed samples. The expected date to begin measurements at this facility is October 2018 although we continue to perform measurements with our current research and development system. This work is supported by Department of Energy, Office of Nuclear Physics, under Contract No. DEAC02-06CH11357.