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| Titel |
Cross-Calibration of Secondary Electron Multiplier in Noble Gas Analysis |
| VerfasserIn |
Alessandro Santato, Doug Hamilton, Michael Deerberg, Jan Wijbrans, Klaudia Kuiper, Claudia Bouman |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105884
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| Publikation (Nr.) |
 EGU/EGU2015-5472.pdf |
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| Zusammenfassung |
| The latest generation of multi-collector noble gas mass spectrometers has decisively
improved the precision in isotopic ratio analysis [1, 2] and helped the scientific community to
address new questions [3]. Measuring numerous isotopes simultaneously has two significant
advantages: firstly, any fluctuations in signal intensity have no effect on the isotope ratio and
secondly, the analysis time is reduced. This particular point becomes very important in static
vacuum mass spectrometry where during the analysis, the signal intensity decays and at
the same time the background increases. However, when multi-collector analysis
is utilized, it is necessary to pay special attention to the cross calibration of the
detectors. This is a key point in order to have accurate and reproducible isotopic
ratios.
In isotope ratio mass spectrometry, with regard to the type of detector (i.e. Faraday or
Secondary Electron Multiplier, SEM), analytical technique (TIMS, MC-ICP-MS or
IRMS) and isotope system of interest, several techniques are currently applied to
cross-calibrate the detectors. Specifically, the gain of the Faraday cups is generally
stable and only the associated amplifier must be calibrated. For example, on the
Thermo Scientific instrument control systems, the 1011 and 1012 ohm amplifiers can
easily be calibrated through a fully software controlled procedure by inputting a
constant electric signal to each amplifier sequentially [4]. On the other hand, the
yield of the SEMs can drift up to 0.2% / hour and other techniques such as peak
hopping, standard-sample bracketing and multi-dynamic measurement must be
used.
Peak hopping allows the detectors to be calibrated by measuring an ion beam of constant
intensity across the detectors whereas standard-sample bracketing corrects the drift of the
detectors through the analysis of a reference standard of a known isotopic ratio. If at least one
isotopic pair of the sample is known, multi-dynamic measurement can be used;
in this case the known isotopic ratio is measured on different pairs of detectors
and the true value of the isotopic ratio of interest can be determined by a specific
equation.
In noble gas analysis, due to the decay of the ion beam during the measurement as well as
the special isotopic systematic of the gases themselves, the cross-calibration of the
SEM using these techniques becomes more complex and other methods should be
investigated.
In this work we present a comparison between different approaches to cross-calibrate
multiple SEM’s in noble gas analysis in order to evaluate the most suitable and reliable
method.
References: [1] Mark et al. (2009) Geochem. Geophys. Geosyst. 10, 1-9. [2] Mark et al.
(2011) Geochim. Cosmochim. 75, 7494-7501. [3] Phillips and Matchan (2013) Geochimica et
Cosmochimica Acta 121, 229-239. [4] Koornneef et al. (2014) Journal of Analytical Atomic
Spectrometry 28, 749-754. |
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