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⁴⁰Ar/³⁹Ar Laboratory


BGC’s 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. The argon data acquisition and reduction program "Mass Spec" (by Alan Deino) is used on all three systems. This software package provides a high degree of flexibility in controlling mass spectrometry functions as well as data analysis (e.g., statistical computations, plateau ages, isochrons, etc.

System 1 features an MAP 215C mass spectrometer with a Nier source, retractable Faraday and stationary 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 40 W CO2 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 a multi-collector Nu Instruments Noblesse mass spectrometer  and is primarily used for archeometric research. This instrument is committed to high-sensitivity 40Ar/39Ar work as required for small, young, and/or low-K materials, and features four ion-counters and an axial Faraday detector for simultaneous ion counting measurement of 40Ar, 39Ar, 37Ar, and 36Ar. 38Ar is also measured on an ion counter, by peak hopping. This system includes an automated extraction line with two sample chambers, a CO2 laser, and an automated cocktail pipette system delivering prescribed mixtures of 36Ar 38Ar, 39Ar, and 40Ar for intercalibrating detectors and determining discrimination and spectrometer sensitivity. Other features (e.g., video monitoring, automated stage translation, automated air-pipette) are analogous to those on System 1.

System 3 features a multicollector IsotopX NGX mass spectrometer with a cold cathode ion source, configured for a diverse range of analytical needs with two detector arrays: One with 5 Faradays for simultaneous measurement of 40Ar, 39Ar, 38Ar, 37Ar, and 36Ar; and a second with 4 Faradays plus a pulse-counting electron multiplier for measuring 36Ar. The Faradays are all coupled with ATONATM amplifiers that extend the useful dynamic range of the detectors down to ion intensities that previously required electron multiplier detectors. The cold cathode source offers enhanced sensitivity and reduced spectrometer backgrounds relative to a traditional filament source, and thus has superior signal to noise. Other features (e.g., laser, video monitoring, automated stage translation, automated air-pipette) are analogous to those on System 1.

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