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Title: Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite.

Abstract

Barium isotopic compositions of single 2.3-5.3 {mu}m presolar SiC grains from the Murchison meteorite were measured by resonant ionization mass spectrometry. Mainstream SiC grains are enriched in s-process barium and show a spread in isotopic composition from solar to dominantly s-process. In the relatively coarse grain size fraction analyzed, there are large grain-to-grain variations of barium isotopic composition. Comparison of single grain data with models of nucleosynthesis in asymptotic giant branch (AGB) stars indicates that the grains most likely come from low mass carbon-rich AGB stars (1.5 to 3 solar masses) of about solar metallicity and with approximately solar initial proportions of r- and s-process isotopes. Measurements of single grains imply a wide variety of neutron-to-seed ratios, in agreement with previous measurements of strontium, zirconium and molybdenum isotopic compositions of single presolar SiC grains.

Authors:
; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Aeronautic and Space Administration (NASA); FOR
OSTI Identifier:
949642
Report Number(s):
ANL/MSD/JA-42786
Journal ID: ISSN 0016-7037; GCACAK; TRN: US201012%%425
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochim. Cosmochim. Acta; Journal Volume: 67; Journal Issue: 17 ; Sep. 2003
Country of Publication:
United States
Language:
ENGLISH
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BARIUM; BARIUM ISOTOPES; GRAIN SIZE; IONIZATION; MASS SPECTROSCOPY; METEORITES; MOLYBDENUM; NUCLEOSYNTHESIS; S PROCESS; SILICON CARBIDES; STARS; STRONTIUM; ZIRCONIUM

Citation Formats

Savina, M. R., Davis, A. M., Tripa, C. E., Pellin, M. J., Clayton, R. N., Lewis, R. S., Amari, S., Gallino, R., Lugaro, M., Univ. of Chicago, Washington Univ., Univ. di Torino, and Cambridge Univ. Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite.. United States: N. p., 2003. Web. doi:10.1016/S0016-7037(03)00083-8.
Savina, M. R., Davis, A. M., Tripa, C. E., Pellin, M. J., Clayton, R. N., Lewis, R. S., Amari, S., Gallino, R., Lugaro, M., Univ. of Chicago, Washington Univ., Univ. di Torino, & Cambridge Univ. Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite.. United States. doi:10.1016/S0016-7037(03)00083-8.
Savina, M. R., Davis, A. M., Tripa, C. E., Pellin, M. J., Clayton, R. N., Lewis, R. S., Amari, S., Gallino, R., Lugaro, M., Univ. of Chicago, Washington Univ., Univ. di Torino, and Cambridge Univ. Mon . "Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite.". United States. doi:10.1016/S0016-7037(03)00083-8.
@article{osti_949642,
title = {Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite.},
author = {Savina, M. R. and Davis, A. M. and Tripa, C. E. and Pellin, M. J. and Clayton, R. N. and Lewis, R. S. and Amari, S. and Gallino, R. and Lugaro, M. and Univ. of Chicago and Washington Univ. and Univ. di Torino and Cambridge Univ.},
abstractNote = {Barium isotopic compositions of single 2.3-5.3 {mu}m presolar SiC grains from the Murchison meteorite were measured by resonant ionization mass spectrometry. Mainstream SiC grains are enriched in s-process barium and show a spread in isotopic composition from solar to dominantly s-process. In the relatively coarse grain size fraction analyzed, there are large grain-to-grain variations of barium isotopic composition. Comparison of single grain data with models of nucleosynthesis in asymptotic giant branch (AGB) stars indicates that the grains most likely come from low mass carbon-rich AGB stars (1.5 to 3 solar masses) of about solar metallicity and with approximately solar initial proportions of r- and s-process isotopes. Measurements of single grains imply a wide variety of neutron-to-seed ratios, in agreement with previous measurements of strontium, zirconium and molybdenum isotopic compositions of single presolar SiC grains.},
doi = {10.1016/S0016-7037(03)00083-8},
journal = {Geochim. Cosmochim. Acta},
number = 17 ; Sep. 2003,
volume = 67,
place = {United States},
year = {Mon Sep 01 00:00:00 EDT 2003},
month = {Mon Sep 01 00:00:00 EDT 2003}
}
  • We report the isotopic composition of molybdenum in twenty-three presolar SiC grains from the Murchison meteorite which have been measured by resonant ionization mass spectrometry (RIMS). Relative to terrestrial abundance (and normalized to s-process-only {sup 96}Mo), the majority of the analyzed grains show strong depletions in the p-process isotopes {sup 92}Mo and {sup 94}Mo and the r-process isotope {sup 100}Mo. Sixteen of these grains have {delta}-values {le} 600% for these three isotopes. The observed isotopic patterns of Mo from mainstream SiC grains clearly reveal the signature of s-process nucleosynthesis. Three-isotope plots of all grain data ({delta}{sup i}Mo vs. {delta}{sup 92}Mo)more » show strong linear correlations with characteristic slopes. This finding suggests mixing of solar-like material and pure s-process material in the parent stars. Comparison with evolutionary calculations of nucleosynthesis and mixing in red giants suggests that low-mass thermally-pulsed symptotic giant branch (TP-AGB) stars are the most likely site for the observed s-process nucleosynthesis.« less
  • Ne isotopes measured in individual presolar graphite grains, solid samples of extinct stars preserved in primitive meteorites, provide information on the type of stellar sources of the grains and on nucleosynthetic mixing and ion-trapping processes which were operating. We present Ne and He isotope analyses of single presolar graphite grains from the KFB1 density fraction extracted from the carbonaceous chondrite Murchison. In addition, we measured isotopes of C, O, and Mg-Al with the NanoSIMS ion microprobe to better constrain the origin of the grains. Eleven out of 51 presolar graphite grains contain nucleosynthetic {sup 22}Ne above our detection limit. Thismore » fraction of {sup 22}Ne-rich grains is similar to the one reported by Nichols et al. although we have a lower {sup 22}Ne detection limit. We detected rare He-shell {sup 20}Ne in one {sup 22}Ne-rich grain and obtained the {sup 20}Ne/{sup 22}Ne ratio (0.03 {+-} 0.02) of the He-shell of an Asymptotic Giant Branch (AGB) star with 1.5-2 M {sub sun} and subsolar metallicity. We also detected {sup 4}He in this grain, while in the other grains, which originally acquired He, He-loss seems to be significant. We found unequivocal evidence for radiogenic {sup 22}Ne (Ne-R) in another graphite grain, which likely condensed in a core-collapse supernova and which incorporated live radioactive {sup 22}Na (t {sub 1/2} = 2.6 yr). For the other grains, a clear assignment to a stellar source is more difficult to make. Putative stellar sources are supernovae, AGB stars, born-again AGB stars, J-type carbon stars, and CO novae.« less
  • Here, we used CHILI, the Chicago Instrument for Laser Ionization, a new resonance ionization mass spectrometer developed for isotopic analysis of small samples, to analyze strontium, zirconium, and barium isotopes in 22 presolar silicon carbide grains. Twenty of the grains showed detectable strontium and barium, but none of the grains had enough zirconium to be detected with CHILI. Nine grains were excluded from further consideration since they showed very little signals (<1000 counts) for strontium as well as for barium. Among the 11 remaining grains, we found three X grains. The discovery of three supernova grains among only 22 grainsmore » was fortuitous, because only ~1% of presolar silicon carbide grains are type X, but was confirmed by silicon isotopic measurements of grain residues with NanoSIMS. And while one of the X grains showed strontium and barium isotope patterns expected for supernova grains, the two other supernova grains have 87Sr/86Sr < 0.5, values never observed in any natural sample before. From their silicon isotope ratios, the latter two grains can be classified as X2 grains, while the former grain belongs to the more common X1 group. The differences of these grains in strontium and barium isotopic composition constrain their individual formation conditions in Type II supernovae.« less
    Cited by 4
  • Presolar graphite is the carrier of Ne-E(L) and most 22Ne in Ne-E(L) had long been attributed to radiogenic decay of 22Na from novae. Of presolar graphite grains with a range of density (1.6-2.2g/cm3), low-density graphite grains extracted from the Murchison meteorite are characterized by 18O excesses and Si isotopic anomalies and are believed to have formed in supenova ejecta. From noble gas analyses of low-density graphite grains, we conclude that 22Ne in the grains is from the in situ decay of 22Na (T1/2=2.6a) produced in the C-burning zone in presupernova stars. The grains also contain Kr that was produced bymore » neutron capture, either in the He-burning zone or the C-burning zone during hydrostatic burning. The 22Ne of a 22Na origin indicates that the grains formed shortly after the explosion. The presence of 22Ne of a 22Na origin and Kr, and the absence of 22Ne of a non-radiogenic origin might give us a further clue for graphite formation in supernova ejecta.« less