| Thermal Ionisation
Mass Spectrometry (TIMS) laboratory
The TIMS laboratory houses a Thermo-Finnigan Triton thermal ionisation instrument (Figure 1) equipped with 9 Faraday collectors , and an electron multiplier |
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Figure
1. ThermoFinnigan Triton TIMS mass spectrometer with oxygen-bleed
valve fed by black oxygen cyclinder on LHS. |
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The 9 collectors (Fixed Axial and 8 moveable) are complimented by a dynamic zoom system that allows optimal cup-alignments (Figure 2).
Image courtesy of ThermoFinnigan. |
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Figure 3. The instrument geometry gives an ion-optical magnification of 2, which has the added, advantage of increasing focal depth and cup-performance (figure 4). The magnet is laminated to give high-speed, low hysteresis mass scanning. Image courtesy of ThermoFinnigan. |
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Faraday
cups are an all-carbon assembly (Figure 4) and combined with the amplifiers,
are capable of measuring signal intensities of up to 50V. The very large
aspect ratio of the cups reduces secondary emission into the analyser
system. The analyser geometry is such that a 17% relative mass spacing
is attainable. The source is easily removable and its design reduces
arcing problems during N-TIMS analysis to insignificant levels.
Figure 4 Deep aspect ratio solid graphite Faraday cups for Triton and Neptune mass spectrometers. Image courtesy of ThermoFinnigan. |
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The analyser system incorporates virtual amplifier technology (figure 5) to cancel-out variations in amplifier gains and hence improve precision. The instrument is specified at 10 ppm (2s) external reproducibility for Sr and Nd isotopic measurements. Figure 5. By means of a relay matrix each current amplifier can be connected to each Faraday cup. As interblock actions the current amplifier are systematically switched to different cups. Finally after a complete run all amplifiers have been connected to all Faraday cups and all signals have been measured with same aberage gain: individual gain uncertainties are cancelled. Image courtesy of ThermoFinnigan. |
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Figure 2. Schematic Diagram of the Triton TIMS, illustrating the main components discussed below. Image courtesy of ThermoFinnigan.
Our Triton instrument is used mainly for low-level (< 10 ng) Sr isotopic measurements [Microsampling] and Os isotopic measurements by both peak switching, for 187Os/188Os and by static measurement of large signals for 187Os/188Os and 186Os/188Os. |
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TIMS
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