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High precision Mg isotope measurements of meteoritic samples by secondary ion mass spectrometry

Luu, Tu-Han and Chaussidon, Marc and Mishra, Ritesh Kumar and Rollion-Bard, Claire and Villeneuve, Johan and Srinivasan, Gopalan and Birck, Jean-Louis (2013) High precision Mg isotope measurements of meteoritic samples by secondary ion mass spectrometry. In: JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, 28 (1). pp. 67-76.

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Official URL: http://dx.doi.org/10.1039/c2ja30187c

Abstract

The possibility of establishing an accurate relative chronology of the early solar system events based on the decay of short-lived Al-26 to Mg-26 (half-life of 0.72 Myr) depends on the level of homogeneity (or heterogeneity) of Al-26 and Mg isotopes. However, this level is difficult. to constrain precisely because of the very high precision needed for the determination of isotopic ratios, typically of +/- 5 ppm. In this study, we report for the first time a detailed analytical protocol developed for high precision in situ Mg isotopic measurements ((25)mg/(24)mg and (26)mg/Mg-24 ratios, as well as Mg-26 excess) by MC-SIMS. As the data reduction process is critical for both accuracy and precision of the final isotopic results, factors such as the Faraday cup (FC) background drift and matrix effects on instrumental fractionation have been investigated. Indeed these instrumental effects impacting the measured Mg-isotope ratios can be as large or larger than the variations we are looking for to constrain the initial distribution of Al-26 and Mg isotopes in the early solar system. Our results show that they definitely are limiting factors regarding the precision of Mg isotopic compositions, and that an under- or over-correction of both FC background instabilities and instrumental isotopic fractionation leads to important bias on delta Mg-25, delta(26)mg and Delta Mg-26 values (for example, olivines not corrected for FC background drifts display Delta Mg-26 values that can differ by as much as 10 ppm from the truly corrected value). The new data reduction process described here can then be applied to meteoritic samples (components of chondritic meteorites for instance) to accurately establish their relative chronology of formation.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to ROYAL SOC CHEMISTRY, ENGLAND
Department/Centre: Division of Mechanical Sciences > Centre for Earth Sciences
Depositing User: Francis Jayakanth
Date Deposited: 18 Mar 2013 05:05
Last Modified: 18 Mar 2013 05:05
URI: http://eprints.iisc.ac.in/id/eprint/46083

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