Welcome to the new Oregon State University Noble Gas Laboratory website.
The site is currently under construction and we appreciate your patience.
The noble gas geochemistry lab was established at OSU through support from a Major Research Instrumentation proposal (PIs Graham, Brook, Duncan and Lupton). This project was funded by the Marine Geology & Geophysics program in NSF’s Division of Ocean Sciences. The primary instrumentation is a noble gas mass spectrometer purchased from Nu Instruments and installed in 2008. Other major lab components include a high-temperature vacuum furnace, and an on-line crushing system, for the extraction of gases from (primarily solid) terrestrial materials.
We have the ability to perform noble gas isotope analyses at a very low level in rocks and minerals, comparable in analytical precision, accuracy and detection limit to the best noble gas labs in the world. The noble gases (helium, neon, argon, krypton, xenon and radon) are unique for their utility in addressing fundamental questions about the history and dynamics of Earth systems. The range of potential scientific applications is very broad and includes many fields of interest to geoscientists, including the origin and evolution the atmosphere and oceans, hydrothermal processes, formation of ore deposits, earthquake/volcanic hazard assessment, ocean circulation, the flux of cosmic dust to the Earth, air-sea gas exchange, surface exposure dating of rocks and sediments, erosion rates and landscape evolution, thermochronology and tectonic uplift of mountain belts, groundwater dating, radionuclide transport and fallout, and nuclear waste disposal. Work carried out in the OSU lab since the first measurements began in 2011 have primarily used high precision analyses of helium isotopes in rocks from mid-ocean ridges, ocean islands and continental rifts to study the chemical geodynamics of the solid Earth, evolution of volcanic systems, and volcanic degassing.
The lab operations are supervised by David Graham. Graham guides graduate student and outside vistor work carried out in the lab, including interpretation and publication of the analytical results. He devotes a major proportion of his time to overseeing, maintaining and developing the lab instrumentation. During normal operation, the lab runs 24 hours a day, but it is monitored remotely by Graham during those nights and weekends.
The noble gas mass spectrometer is a low volume instrument operated under static vacuum, and has a high sensitivity ion source (Nier-type). Typical sensitivity is 0.23 mA torr-1 for 4He and 1.7 mA torr-1 for 40Ar at 400 mA. The instrument is all-metal construction and can be baked to reach low background levels and low static gas rise rates, particularly important for the isotope analysis of small amounts of noble gases. The OSU Noblesse instrument is fitted with a single faraday cup and 3 ion counting detectors. The high mass ion counter position is shared with the faraday with switching via an electrostatic deflector. The central and low mass ion counting detectors have a special filter to eliminate scattered, low energy ions that may interfere with small ion beams (especially important when trying to measure very small amounts of 3He in the presence of large amounts of 4He, for example). The Noblesse is a variable dispersion instrument employing patented, electrostatic “zoom optics” derived from the Nu Plasma ICP-MS. It performs the 3He/4He measurement in a pseudo high-resolution mode that partially resolves 3He from HD++H3+, but any tailing from the HD++H3+ beneath the peak-flat where 3He is measured is virtually absent. The instrument also allows simultaneous collection of 20Ne, 21Ne and 22Ne, and rapid peak switching to measure 40Ar+ and CO2+ during the Ne analysis to monitor potential contributions of doubly charged interfering species. 36Ar, 38Ar and 40Ar can be measured simultaneously, with a choice between ion counting or faraday detection for the 40Ar peak depending upon sample size. Kr and Xe isotopes can be measured via peak jumping.
The gas extraction line has a computer-controlled sample processing and introduction system connected to the mass spec inlet. This consists of a Janis cryogenic cold trap for routine separation of the noble gases (cryostat temperature control to ~8 °K is maintained by a closed-loop compressor), air-actuated pneumatic valves, heated SAES getters, pressure sensors, and oil-free vacuum pumps (turbomolecular, scroll and ion) to minimize hydrocarbons. Air and specialized gas standards are automatically pipetted in known quantity (0.1 cm3) for routine calibration of the mass spectrometer.
The high-temperature vacuum furnace is used for melting and step-heating of rocks, minerals and sediments. It has a tantalum resistive heating element and a central Ta crucible. This is surrounded by a series of heat shields and the whole assembly is contained in a water cooled chamber which is independently pumped from the main vacuum line (via a diffusion pump with a backing rotary pump). Cooling is maintained by a dedicated water chiller having a minimum flow rate of 2 l min-1. The pressure of the secondary vacuum is monitored using a Penning gauge and furnace power is interlocked to this measurement and the chiller water flow. A disposable Ta liner contains samples dropped into the furnace and minimizes chemical reaction with the crucible walls. Samples are introduced by a low volume carousel that allows up to 12 samples to be loaded under vacuum simultaneously. A viewport enables the viewing of samples during heating, as well as monitoring the crucible temperature independently with an optical pyrometer if desired. The temperature of the furnace is monitored with a W/W-Re thermocouple and controlled using a dedicated controller interfaced to a computer. Different heating profiles may be stored for use in different experiments.
The sample processing line also includes a stainless steel rock crushing manifold, for in vacuo crushing of rock and mineral samples to release gases from fluid and melt inclusions.
