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.