Burchell, M.J.

Franchi, I.A.

Graham, G.A.

Kearsley, A.T.

Wright, I.P.

English

Open Research Online 

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsCharacterisation of extraterrestrial samples by Ramanand Electron microprobesConference or Workshop ItemHow to cite:Kearsley, A.T.; Franchi, I.A.; Graham, G.A.; Wright, I.P. and Burchell, M.J. (2001). Characterisation of extraterrestrialsamples by Raman and Electron microprobes. In: 64th Annual Meeting of the Meteoritical Society, 10-14 Sep 2001,Vatican City, Italy.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/metsoc2001/pdf/5296.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.uk  CHARACTERISATION OF EXTRATERRESTRIAL SAMPLES BY RAMAN AND ELECTRON MICROPROBES.  A. T. Kearsley1, I. A. Franchi2, G. A. Graham2, I. P. Wright2 and M. J. Burchell3, 1 School of Biological and Molecular Sciences, Oxford Brookes University, Oxford OX3 0BP, United Kingdom, 2 Planetary and Space Sciences Research Institute, The Open University, Milton Keynes, UK.  3 Unit for Space Sci-ences and Astronomy, University of Kent at Canterbury, UK.   Introduction:  Returned extraterrestrial samples, planetary, asteroidal or cometary, are so valuable that initial assessment of the most appropriate analytical protocols for each grain is essential. It is particularly important to know the distribution and interrelation-ships of specific mineral components.  Numerous so-phisticated microanalysis techniques are now available [1], yet many may damage vulnerable volatile-rich materials, or produce surface contamination, if em-ployed at too early a stage.  How should one characterise individual particles, preferably without exposure to atmosphere, or removal from the capture medium (eg. foil, or aerogel block), before commitment to carefully sequenced destruc-tive analysis?   We suggest that new Raman and electron micro-probes may provide the necessary chemical and min-eralogical information, with minimal specimen modifi-cation.  Techniques employed:   X-ray mapping of uncoated samples. Composi-tional (backscattered) electron imagery of grain sur-faces usually employs a conductive coat of carbon, or may be performed without coating in a low-pressure atmosphere of Ar, or He and Nitrous Oxide. Each sys-tem has limitations for samples from which isotopic measurements of noble gases or carbon-bearing phases are required.  We have used an Oxford Instrument eXL X-ray microanalyser on a JSM 840 SEM operating at 20 kiloVolts, 2 nanoAmperes and high vacuum, to create images of small (3mm) uncoated shards of the meteor-ite Los Angeles 001, supported on a conductive cradle.  Rapid energy-dispersive mapping (40 milliseconds, 16,000 point array) was performed for 23 characteristic X-ray energies [2]. The distribution of pyroxenes, feld-spathic glass, accessory sulfides and phosphates, and terrestrial contamination by carbonate growth were all easily seen. Raman microprobe analysis and mapping. The ap-plication of Raman techniques to mineral grains im-pacted into aerogel samples has been previously dem-onstrated [3] & [4]. We used a JY LabRaman micro-probe at the Open University to create a reference li-brary of spectra for silicates, carbonates and oxides, as well as SiC, diamond, and other carbon-bearing phases. Confocal sampling by the LabRaman allows acquisition from a small, well-defined volume, as little as 2 micrometres in diameter. Beam scanning and automated stage-movement permit rastering in 3 di-mensions, thereby creating stacked map-slices of a grain. The spatial distribution of each mineral compo-nent within a slice can be displayed (figure 1).     Figure 1.   LabRaman maps of olivine and organic matter within particle of Allende, impacted by light gas gun shot into aerogel.  High-resolution maps may take several hours to generate, fortunately our experiments show that con-tinuous irradiation by an 8mW, 514.5nm Argon ion laser at a tightly-focused single point on serpentine yields no appreciable change in Raman spectral properties over a time exceeding twelve minutes.  Conclusions: Modified analytical SEM and mod-ern Raman microprobes have substantial promise for initial, non-destructive characterization of extraterres-trial samples. References: [1] Zolensky M. E. et al. (2000) MAPS, 35, 9-29. [2] Graham G. A. et al. (2001) Proc. 3rd European Conf. Space Debris, in press. [3] Burchell M. J. et al. (2001) MAPS, 36, 209-221. [4] Graham G. A. et al. (2001) LPS XXXII, Abstract #1637.   64th Annual Meteoritical Society Meeting (2001) 5296.pdf

Characterisation of extraterrestrial samples by Raman and Electron microprobes

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Characterisation of extraterrestrial samples by Raman and Electron microprobes

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