Noble gases analysis by static mass spectrometry Theory and instrumentation

Since the 1950s, the geochemistry of noble gases has developed considerably thanks to advances in mass spectrometry. Today, they are considered by the geosciences community as powerful tracers, thanks in particular to their chemical inertia with respect to the environment in which they are found. Their concentrations in certain minerals, for example, currently make it possible to quantify the exhumation and erosion rates of our landforms using thermochronology methods, or to provide dating tools (K/Ar, Ar/Ar, U-Th-Sm/He methods, cosmogenic isotopes ³ He, ²¹ Ne and ³⁸ Ar) essential to archaeology, volcanology, paleoclimatology, cosmochemistry, etc. Additional constraints on the origin and evolution of noble gases can also be provided using their isotopic signatures (e.g. ³ He/ ⁴ He; ²⁰ Ne/ ²² Ne, ²¹ Ne/ ²² Ne; ⁴⁰ Ar/ ³⁶ Ar, ³⁸ Ar/ ³⁶ Ar...). These make it possible, for example, to highlight the presence of isotopes of cosmogenic origin ( ³ He, ²¹ Ne, ³⁸ Ar, ⁷⁸ - ⁸³ Kr, ¹²⁴ - ¹²⁸ Xe), radiogenic ( ⁴ He, ⁴⁰ Ar, ¹²⁹ Xe), nucleogenic ( ²¹ Ne) or fissiogenic (e.g. ¹³¹ - ¹³⁶ Xe). The use of isotope ratios makes it possible to trace the origin of volcanic gas sources (e.g. crust, upper or lower mantle) emanating from the Earth's surface, or to highlight mass-dependent fractionation processes during physical processes such as diffusion or condensation/evaporation.

However, all these applications require the rare gases to be extracted under ultra-high vacuum in a chamber. This chamber is connected to a mass spectrometer via a second chamber called the purification line. The extraction method (grinding, ablation, fusion) used to extract...