Atom Trap Trace Analysis of Rare Noble Gas Isotopes

Atom Trap Trace Analysis (ATTA) is an efficient and highly selective laser-based atom counting method where neutral atoms of the desired isotope are captured by laser light in a magneto-optical trap and detected one-by-one via laser induced fluorescence. ATTA is unique among trace analysis techniques in that it is free of interferences from any other isotopes, isobars, atomic or molecular species. At Argonne, we have brought this novel technique from a proof-of-principle concept all the way to a routine analytical tool that is now available at large to the Earth science community and beyond. Currently, we concentrate on two long-live krypton isotopes: Kr-81 (half-life = 230,000 yrs) as an ideal tracer for old water and ice with mean residence times in the range of 10⁵–10⁶ years, and the anthropogenic isotope Kr-85 (half-life = 10.8 yrs) for dating respectively young ground waters. Both isotopes can now be routinely analyzed via ATTA in samples as small as 5 microliters of krypton gas (STP). More generally, other rare noble gas isotopes such as Ar-39 and He-3 are amenable to ATTA analysis, and particular, ATTA Ar-39 instruments are currently under development at the University of Heidelberg and the University of Science and Technology of China. I will present the current state-of-the-art of the ATTA technique, examples of recent applications, and how this technology can relate to low-radioactivity noble gas materials. This work is supported by Department of Energy, Office of Nuclear Physics, under Contract No. DEAC02-06CH11357.

This presentation was used for the Low-Radioactivity Underground Argon Workshop held at Pacific Northwest National Laboratory in Richland, Washington on March 19 - 20, 2018.