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New Mexico Geochronology Research Laboratory
Hardware

The components necessary for argon isotopic analyses of geologic samples are 1) the extraction system and 2) the mass spectrometer. The extraction system, in turn, consists of several components: 1)a heating device and 2) an extraction line. The heating device is what physically drives the argon gas out of the sample. Common heating devices are furnaces and lasers. The extraction line is a network of stainless steel tubing, valves, pumps and "filters" that purify the argon and allow it to travel from the heating device to the mass spectrometer. Once to the mass spectrometer, the argon isotopes are seperated from each other according to their weight and analyzed.

Extraction System

Tent Rocks Panorama
Generalized schematic of the NMGRL Extraction System and Mass Spectrometer. The red/green circles are computer controlled, pneumatically operated valves. The gray circles are manual valves.

The NMGRL argon extraction system constists of:

Component
Description

Heating devices

Furnace, CO2 Laser, UV Laser and Mechanical Crusher.

Pumps

Four Varian V-70 turbomolecular pumps backed by Varian, Alcatel or Pfeiffer rotary vane pumps provide the ultra-high vacuum (~10-9 torr) necessary for ultra-precise argon geochronology.

Getters

Three SAES-Getters model ST-101 getter cartridges fitted with heater units. Two ST-101 getters run at 450°C, one at room temperature. The getters scrub the extracted sample gas of non-noble gas species (e.g. CO2, H2O, SO2, etc.) before it enters the mass spectrometer.

Air pipette system

Bottle of atmospheric argon necessary for determining isotopic discrimination of the mass spectrometer.

Quadrupole

Quadrupole mass spectrometer; ideal for pre-sampling of extracted sample gas before entering mass spectrometer. Also vital for finding potentially damaging leaks in the vacuum system.

Ion pressure gauges

Three ion gauges monitor the pressure of the ultra-high vacuum system.

Mass Spectrometer

Tent Rocks Panorama
Generalized cartoon of the operation of the MAP 215-50 mass spectrometer used by the NMGRL.

The NMGRL operates a Mass Analyzer Products Limited (MAP) 215-50 noble gas mass spectrometer.

Specifications:

  • Nier type ion source
    • filament
    • electron trap
    • ion repeller
    • focussing half-plates
    • defining and alpha slit
  • Magnet
    • 90° magnetic sector field
    • 15 cm radius
    • nominal 26.5° entrance/exit angle
    • 5 cm radius electostatic analyzer
    • Current or Hall probe field controlled
  • Collectors
    • Pfeiffer SEM-217 electron multiplier
    • Faraday cup collector
  • Vacuum
    • 30 liter per second Varian Triode ion pump
    • pressure = less than 10-9 torr
  • Getter
    • single SAES Getter ST-101 getter cartridge with activation heater (normally operated at room temperature)