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Title: Strontium and barium isotopes in presolar silicon carbide grains measured with CHILI—two types of X grains

Abstract

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 grains 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 formationmore » conditions in Type II supernovae.« less

Authors:
 [1]; ORCiD logo [1];  [2];  [3];  [1];  [4];  [1];  [1];  [5];  [6];  [2]
  1. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences; Chicago enter for Cosmochemistry, Chicago, IL (United States)
  2. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences, Enrico Fermi Inst.; Chicago enter for Cosmochemistry, Chicago, IL (United States)
  3. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences, Enrico Fermi Inst.; Chicago enter for Cosmochemistry, Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States). Materisl Science Division
  4. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences; Argonne National Lab. (ANL), Argonne, IL (United States). Materisl Science Division
  5. Washington Univ., St. Louis, MO (United States). Lab. for Space Sciences, Dept. of Physics
  6. Max Planck Inst. for Chemistry, Mainz (Germany)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE; National Aeronautics and Space Administration (NASA)
OSTI Identifier:
1414348
Report Number(s):
LLNL-JRNL-729492
Journal ID: ISSN 0016-7037; TRN: US1800684
Grant/Contract Number:
AC52-07NA27344; NNX07AL94G; NNX11AC21G; NNX15AF78G; NNX12AL85HNNX09AG39G
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 221; Journal Issue: C; Journal ID: ISSN 0016-7037
Publisher:
The Geochemical Society; The Meteoritical Society
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; presolar grains; silicon carbide; supernovae; nucleosynthesis; resonance ionizatoin mass spectrometry (RIMS); strontium isotopes; barium isotopes

Citation Formats

Stephan, Thomas, Trappitsch, Reto, Davis, Andrew M., Pellin, Michael J., Rost, Detlef, Savina, Michael R., Jadhav, Manavi, Kelly, Christopher H., Gyngard, Frank, Hoppe, Peter, and Dauphas, Nicolas. Strontium and barium isotopes in presolar silicon carbide grains measured with CHILI—two types of X grains. United States: N. p., 2017. Web. doi:10.1016/j.gca.2017.05.001.
Stephan, Thomas, Trappitsch, Reto, Davis, Andrew M., Pellin, Michael J., Rost, Detlef, Savina, Michael R., Jadhav, Manavi, Kelly, Christopher H., Gyngard, Frank, Hoppe, Peter, & Dauphas, Nicolas. Strontium and barium isotopes in presolar silicon carbide grains measured with CHILI—two types of X grains. United States. doi:10.1016/j.gca.2017.05.001.
Stephan, Thomas, Trappitsch, Reto, Davis, Andrew M., Pellin, Michael J., Rost, Detlef, Savina, Michael R., Jadhav, Manavi, Kelly, Christopher H., Gyngard, Frank, Hoppe, Peter, and Dauphas, Nicolas. Wed . "Strontium and barium isotopes in presolar silicon carbide grains measured with CHILI—two types of X grains". United States. doi:10.1016/j.gca.2017.05.001. https://www.osti.gov/servlets/purl/1414348.
@article{osti_1414348,
title = {Strontium and barium isotopes in presolar silicon carbide grains measured with CHILI—two types of X grains},
author = {Stephan, Thomas and Trappitsch, Reto and Davis, Andrew M. and Pellin, Michael J. and Rost, Detlef and Savina, Michael R. and Jadhav, Manavi and Kelly, Christopher H. and Gyngard, Frank and Hoppe, Peter and Dauphas, Nicolas},
abstractNote = {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 grains 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.},
doi = {10.1016/j.gca.2017.05.001},
journal = {Geochimica et Cosmochimica Acta},
number = C,
volume = 221,
place = {United States},
year = {Wed May 10 00:00:00 EDT 2017},
month = {Wed May 10 00:00:00 EDT 2017}
}

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  • 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 initialmore » 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.« less
  • In terms of nucleosynthesis issues alone, we demonstrate that the type X silicon carbide particles have chemical and isotopic compositions resembling those from explosive helium burning in {sup 14}N-rich matter. These particles are extracted chemically from meteorites and were once interstellar particles. They have already been identified by their discoverers as supernova particles on the basis of their isotopic compositions, but we argue that they are from supernovae of Type Ia that explode with a cap of helium atop their CO structure. The relative abundances of the isotopes of C and Si and trace N, Mg, and Ca match thosemore » in the X particles without need of complicated and arbitrary mixing postulates. Furthermore, both C and Si abundances are enhanced and more abundant than O, which suggests that SiC is in fact the natural condensate of such matter. We also briefly address special issues relevant to the growth of dust within Type Ia interiors during their expansions. {copyright} {ital 1997} {ital The American Astronomical Society}« less
  • The strontium, zirconium, molybdenum, and barium isotopic compositions predicted in the mass-losing envelopes of asymptotic giant branch (AGB) stars of solar metallicity and mass 1.5, 3, and 5 M{sup {circle_dot}} are discussed and compared with recent measurements in single presolar silicon carbide (SiC) grains from the Murchison meteorite. Heavy-element nucleosynthesis via the s-process occurs in the helium intershell, the region between the helium-burning and hydrogen-burning shells, producing heavy elements beyond iron. After a limited number of thermal runaways of the helium shell (thermal pulses), at the quenching of each instability, the convective envelope penetrates into the top layers of themore » helium intershell (third dredge-up), mixing newly synthesized {sup 12}C and s-process material to the stellar surface. Eventually, the envelope becomes carbon-rich (C {>=} O), a necessary condition for SiC grains to condense. In the helium intershell, neutrons are released by (a, n) reactions on {sup 13}C and {sup 22}Ne during interpulse phases and the thermal pulses, respectively. A {sup 13}C pocket is assumed to form in a tiny region in the top layers of the helium intershell by injection of a small amount of protons from the envelope during each third dredge-up episode. This {sup 13}C then burns radiately during the interpulse phase. The average neutron density produced is low, but of long duration, so the total neutron exposure is high. We have explored a large range of possible {sup 13}C abundances in the pocket. In low-mass AGB stars (1.5 M{sup {circle_dot}} {<=} M {<=} 4 M{sup {circle_dot}}), a second small burst of neutrons is released by marginal {sup 22}Ne burning in the thermal pulse. The neutron density reaches quite a high peak value but is of short duration, so the neutron exposure is low. In intermediate-mass AGB stars (4 M{sup {circle_dot}} < M {<=} 8 M{sup {circle_dot}}), the {sup 22}Ne neutron source is more efficiently activated. The neutron capture process has been followed with a postprocessing code that considers all relevant nuclei from {sup 4}He to {sup 210}Po. The predicted isotopic compositions of strontium, zirconium, molybdenum, and barium in the envelopes of low-mass AGB stars of solar metallicity are in agreement with the isotopic ratios measured in individual presolar SiC grains, whereas predictions for intermediate-mass stars exclude them as the sources of these grains. A multiplicity of low-mass AGB stars with metallicity around solar, having different masses and experiencing different neutron exposures, are required to account for the measured spread in heavy-element isotopic compositions among single presolar SiC grains. The range of neutron exposures corresponds, on average, to a lower mean neutron exposure than that required to reproduce the s-process main component in the solar system.« less
  • We have made improved measurements of the {sup 142,144}Nd(n,{gamma}) cross sections and investigated the {ital s}-process nucleosynthesis in the Ce-Nd-Sm region. Recently discovered anomalies of the Nd isotopes in silicon carbide grains from the Murchison meteorite have been interpreted in terms of pure {ital s}-process material from an AGB star. With previous cross section data the {ital s}-process origin could not be confirmed, whereas our new data convincingly support the interpretation that these isotopic anomalies were carried into the early solar system inside carbon dust particles that condensed in outflowing winds of presolar AGB stars. {copyright} {ital 1997} {ital Themore » American Physical Society}« less
  • The isotopic composition of zirconium in silicon carbide grains from the Murchison meteorite was measured by resonant ionization mass spectrometry of laser-ablated neural atoms. These grains are condensates from the atmospheres of red giant stars that existed before the formation of our sun and solar system, and they contain records of nucleosynthesis in these stars. The r-process-dominated isotope zirconium-96 was depleted by more than a factor of 2 compared with the s-process-dominated isotopes zirconium-90, zirconium-91, zirconium-92, and zirconium-94, in agreement with expectations for neutron capture nucleosynthesis in asymptotic giant branch stars. 44 refs., 2 figs., 1 tab.