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He
Mass Spec
| Noble
Gas Mass Spec
| Ar
Mass Spec
| SF6
GC
| Gas
Extraction Lab
| He
MS Report
The Ar lab facility was designed for 40Ar/39Ar measurements of small samples, and consists of a fully custom built and automated micro-extraction system and a VG5400 mass spectrometer.
The Ar mass spectrometer employs a modified Neir ion-source and a 90Á sector extended-geometry. The mass spectrometer is operated in static mode. M/e 36 cold procedural blanks for both the extraction system and mass spectrometer are less than 5 x 10-14 cc STP. Desorption of 40Ar in the stainless steel wall of the vacuum envelope is less than 1 x 10-12 cc STP/min. The detection limit of the VG5400 is approximately 1 x 10-14 cc STP (~5 x 10-19 moles), or about 1 x 10-3 Amps/Torr at 200mA trap current.
The laser and beam delivery system consists of coaxial CO2 and UV lasers and a video camera and a Newport x-y-z stage. The system can produce up to three measurements per hour.
Automation of the vacuum valves is achieved by using pneumatically operated valves that are activated by electro-pneumatic solenoid valves. Gasses released from the heating of samples are scrubbed of reactive gases such as H2 CO2, CO and N2 by exposure to Zr-Fe-V and Zr-Al sintered metal alloy getters. The remaining inert gasses, principally Ar, are then admitted to the mass spectrometer and the Ar-isotopic ratios are determined using automated data collection software (Al Deino, Berkeley Geochronology Center).
October 10, 2003