High-resolution Stepped Heating Analyses of Murchison Residues Using Resonance Ionization of Xenon

Details High-resolution Stepped Heating Analyses of Murchison Residues Using Resonance Ionization of Xenon High-resolution Stepped Heating Analyses of Murchison Residues Using Resonance Ionization of Xenon

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.373j&link_type=abstract

Meteoritics, vol. 28, no. 3, volume 28, page 373

Computer Science

Murchison, Resonance Ionization Spectroscopy, Xenon

Scientific paper

RELAX [1] (Refrigerator-Enhanced Laser Analyzer for Xenon) is an ultrasensitive mass spectrometer designed for the analysis of xenon from meteorite samples. It combines a selective, resonance ionization ion source that has a cryogenic sample concentrator with a low-volume (400 cc) time-of- flight mass analyzer. Acid residues have been prepared from the Murchison meteorite by methods similar to those of Tang et al. [2]. Sample MM was produced from an interior sample of the Murchison C2 chondrite by HF/HCl treatment. A portion of this was oxidized using Cr2O7- followed by HClO4 to produce MM1. A proportion of C delta was removed from some of this into an ammonia suspension, leaving sample MM2 as a residue. Samples of MM1 and MM2 were analyzed by direct loading onto previously degassed filaments constructed by spot welding strips of Ta ribbon onto vacuum feedthroughs and mounting them in the sample extraction chamber. The samples were mounted in well-localized spots to minimize variations in temperature. Gas was released in a series of temperature steps, each of which were 5 min in duration; typically the filament required an initial 1 min to achieve equilibrium. Repeat extractions were made at each temperature stage in an attempt to degas the sample at that temperature before increasing the filament current. Typically 10 separate temperature steps, each consisting of at least 4 extractions, contained evidence of the presence of Xe-HL, the exotic xenon component associated with C-delta microdiamonds. No trace of Xe-s was detected in any filament furnace analysis, although it has been released from smaller quantities (25 micrograms) of residue MM2 by laser heating. Indeed, small amounts of Xe-HL were usually still evolving when the analysis was terminated as the filament broke. Figures 1 and 2 show three isotope plots appropriate to the examination of the heavy and light components of Xe-HL from stepped heating of sample MM1b (215 micrograms). The data points are compiled from the sums of the gas released in each analysis at a given temperature step, which consisted of up to nine separate heatings. The data are consistent with mixing between a Xe-HL end member from a previous study of the Murchison meteorite [3] and a planetary component. The ability of RELAX to make reliable measurements on gas samples smaller than previously possible underlines its potential contribution to the understanding of presolar xenon components. References: [1] Gilmour J. D. et al., Rev. Sci. Instr., submitted. [2] Tang M. et al. (1988) GCA, 52, 1221-1234 [3] Alaerts L. et al. (1980) GCA, 44, 189- 209. Figure 1 appears here in the hard copy.

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