TRACING NOBLE GAS RADIONUCLIDES IN THE ENVIRONMENT*

Trace analysis of radionuclides is an essential and versatile tool in modern science and technology. Because of their ideal geophysical and geochemical properties, long-lived noble gas radionuclides—particularly ³⁹Ar (t1/2 = 269 y), ⁸¹Kr (t1/2 = 2.3 × 10⁵ y), and ⁸⁵Kr (t1/2 = 10.8 y)—have long been recognized to have a wide range of important applications in Earth sciences. In recent years, significant progress in the development of practical analytical methods has led to applications of these isotopes in the hydrosphere (tracing the flow of groundwater and ocean water). In this article, we introduce the applications of these isotopes and review three leading analytical methods: low-level counting (LLC), accelerator mass spectrometry (AMS) and atom trap trace analysis (ATTA).