Technical Note: Design, construction, automation, and calibration of a low-volume He measurement line optimized for laser-ablation analyses

Abstract. A noble-gas analysis line capable of accurate and precise measurements of small absolute amounts of ⁴He released from crystals is a key analytical step in the production of (U-Th)/He chronologic data. He analysis lines that are custom-built in-house can be optimized for specific lab needs and facilitate continued maintenance, repair, and upgrades. However, there is little information in the published literature about the methods and approaches for building a He line. Here, we describe the design, construction, automation, and metrological calibration of a custom ⁴He extraction and analysis line as part of establishing laser-ablation (U-Th)/He methods in the University of Colorado Thermochronology Research and Instrumentation Lab (CU TRaIL). The line, called the Jimbochron, is designed to precisely measure very small (~fmol) amounts of ⁴He while being fully automated and easily modifiable in the future. These goals are achieved by minimizing the line volume, adopting a unique double-hexagonal manifold configuration, installing a high-sensitivity quadrupole mass spectrometer, and developing LabView code for instrument communication and automation that is open and straightforward to update. We also explain the steps used to calibrate the Jimbochron metrologically from first principles with a new in-house calibration volume to ensure high-accuracy He measurements. The Jimbochron is about two orders of magnitude more sensitive than our existing ⁴He line and now routinely generates accurate and precise He data for laser-ablation (U-Th)/He applications.