The UW-Madison Rare Gas Geochronology Laboratory occupies 600 square feet in two adjacent rooms. One room, equipped with a balance, binocular and polarizing/petrographic microscopes, and clean work benches, is used exclusively for the preparation of samples for ⁴⁰Ar/³⁹Ar analyses and storage of irradiated materials. The other houses a six-foot fume hood for sample preparation, and the ⁴⁰Ar/³⁹Ar analytical system.

The laser manifold has two SAES GP-50 getters. Each manifold has its own automated air pipette used for mass discrimination measurements. The dual furnaces and laser chambers allow us to load and pump down samples in one part of the line while continuing measurements, thus we experience virtually no down-time when breaking vacuum to change samples and are performing analyses > 160 hours per week. The sensitivity of the spectrometer is 1.1 x 10^-14 moles of ⁴⁰Ar/Volt, thus enabling measurements of small samples ranging from sub-milligram sanidine crystals of Miocene or older age to 100 mg packets of groundmass from K-poor latest Pleistocene-Holocene basalts, andesites, and rhyolites.The furnace and laser manifolds are both pumped via a pair of turbo-molecular and ion pumps, resulting in low and stable blanks.

Working closely with Lee Powell, the department’s senior electrical engineer, the analytical system, including resistance furnaces, the CO₂ laser, UHV valves on the manifolds, and the mass spectrometer, have been fully automated. Automation codes are written and modified in a user-friendly LabView® software package. Since April, 2000 we have determined ages from >10,000 mineral samples using laser fusion or laser incremental heating techniques and over 1000 Pliocene to Holocene lava samples have been dated via incremental heating using the resistance furnaces. Data output files from the mass spectrometer are read by ArArCALC which is an Excel® workbook-based program that allows considerable flexibility in reducing and blank-correcting ⁴⁰Ar/³⁹Ar isotope data, and has outstanding archival functionality (Koppers, 2002).