40Ar/39Ar Laboratory

Virtual Tour Argon LabA state of the art 40Ar/39Ar laboratory, featuring three fully automated gas extraction-mass spectrometry systems, is used for dating rocks and minerals by methods based on the natural radioactive decay of potassium. These systems can be used to date samples as young as 2,000 years, and as old as the Earth itself (4.6 billion years), depending on the nature of the sample.

System 1 features an MAP 215C mass spectrometer with a Nier source, retractable Faraday and stationery Balzers electron multiplier detectors, and adjustable collector slit. The mass spectrometer is mated on-line to a fully automated extraction line with two C-50 getters and a cryogenic condensation trap. Samples are loaded into a UHV chamber mounted on an automated translating x-y stage and degassed with a 6 W Coherent Inova 90 continuous argon-ion laser. A video camera and monitor allow magnified observation of the sample chamber. An automated air pipette system allows periodic monitoring of sensitivity and mass discrimination. All aspects of sample degassing, gettering, and mass spectrometry are controlled by software developed by BGC, and run on a Macintosh computer.

System 2 features an MAP 215-50 mass spectrometer, which is similar to the MAP 215C on System 1 in most respects except that it uses an electrostatic filter in conjunction with the electron multiplier detector. The extraction line is analogous in all respects to that of System 1 except that it uses a Nd-YAG laser, which can be used in either continuous or pulsed mode. System 2 also features a fully automated, double vacuum, electrical resistance furnace for heating samples up to 1650 °C. The furnace uses infrared radiation from the crucible, calibrated against either optical pyrometry or thermocouple measurements, to provide feedback to the power supply.

System 3 features a custom-designed MAP 215-50 mass spectrometer with dual electron multipliers (permitting simultaneous measurement of masses 36 and 40) in addition to a retractable Faraday cup. The mass spectrometer is mated to a highly flexible extraction line dubbed "Nexus", with a CO2 laser. Twin sample chambers allow bake-out of one while the other is engaged in analysis. Other features (e.g., video monitoring, automated stage translation, automated air-pipette) are analogous to those on Systems 1 and 2. Sample temperature during laser heating can be measured via a Mikron two-color infrared pyrometer system.