A new capability in isotope geochemistry



International Workshop on Tracer Applications of Noble Gas Radionuclides; Argonne, Illinois, 21–22 June 2012 The noble gas radionuclides krypton-81 (81Kr; 229,000-year half-life), krypton-85 (85Kr; 10.8-year half-life), and argon-39 (39Ar; 269-year half-life) have ideal properties for tracing fluid transport in Earth systems. Their principal applications include determination of groundwater residence times (81Kr, 85Kr, and 39Ar) and seawater ventilation ages (39Ar). In practice, however, few studies have employed noble gas radionuclides because of the large sample sizes required and the complex analytical systems required for measuring their extremely low isotopic abundances (10–16 to 10–11). Most published studies have used low-level radioactive decay counting for 39Ar and 85Kr, but the low activity of 81Kr has necessitated the development of various atom-counting methods over the past 4 decades.