Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28q.353g&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 353
Astronomy and Astrophysics
Astrophysics
Murchison, Pyrolysis, Resonance Ionization Spectroscopy, Xenon
Scientific paper
The ultrasensitivity of the Relax [1] mass spectrometer allows higher resolution stepped pyrolysis experiments than previously possible. A series of acid residue samples from the Murchison meteorite has been prepared and we are engaged in a study of them using a filament microfurnace. A sample of 125 micrograms of residue MM2 (MM2c) was directly loaded onto a degassed tantalum filament and analyzed in a series of 29 temperature steps, at least two analyses being carried out at each temperature. The limit in resolution was imposed by the current control of the extraction furnace presently being used. For the purposes of this abstract the total gas released over all analyses at each temperature is used, thus data points represent measurements at specific temperatures. Precise measurement of the enrichment in heavy and light isotopes associated with Xe-HL was possible for the gas released in 21 of the 29 temperature steps. No independent temperature measurement was made, however it seems likely that these covered the range 1000 degrees C to 1600 degrees C where Xe-HL has previously been observed to be released (for instance [2]). There does not appear to be any internal variation in the heavy and light subcomponents: a three isotope plot of ^124Xe/^130Xe against ^126Xe/^130Xe is consistent with a mixture between planetary xenon and a Xe-HL component previously measured in this meteorite [2], as is a three isotope plot of ^134Xe/^130Xe against ^136Xe/^130Xe. Figure 1 shows a three isotope plot of ^124Xe/^130Xe against ^136Xe/^130Xe for the data points containing HL enrichment. If the data indeed represent a mixing between planetary and a single Xe-HL component they should lie along the line P-HL while an admixture of terrestrial xenon would cause them to occupy triangle P-T-HL. The actual data show significant enrichment in ^124Xe, the maximum being at least three standard deviations above the P-HL mixing line. Figure 2 shows a graph of the excess ^124Xe to excess ^136Xe for each of these samples against the percentage of total excess ^136Xe released, i.e., fractional release of H-Xe. It thus shows how the ratio of the heavy and light components varies with increasing temperature. There is some evidence for a release of an HL component relatively depleted in L-Xe in the lower temperature steps and subsequent release of an HL component enriched in L-Xe, possibly held in a carrier of larger grain size. These results, if confirmed in subsequent experiments, would have important implications for the modeling of Xe-HL production. The heavy and light components are expected to be produced in different nucleosynthetic environments [3] so a variation in Xe-HL could reflect differing formation conditions of the associated carrier. References: [1] Gilmour J. D. et al. (submitted) G. Rev. Sci. Inst. [2] Alaerts L. et al. (1980) GCA, 44, 189-209. [3] Clayton D. D. (1989) Astrophys. J., 340, 613-619.
Arden John W.
Gilmour James D.
Johnston W. A.
Lyon Ian C.
Turner Gary
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