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Title: SULFUR ISOTOPIC COMPOSITIONS OF SUBMICROMETER SiC GRAINS FROM THE MURCHISON METEORITE

We report C, Si, N, S, Mg-Al, and Ca-Ti isotopic compositions of presolar silicon carbide (SiC) grains from the SiC-rich KJE size fraction (0.5-0.8 μm) of the Murchison meteorite. One thousand one hundred thirteen SiC grains were identified based on their C and Si isotopic ratios. Mainstream, AB, C, X, Y, and Z subtypes of SiC, and X-type silicon nitride (Si{sub 3}N{sub 4}) account for 81.4%, 5.7%, 0.1%, 1.5%, 5.8%, 4.9%, and 0.4%, respectively. Twenty-five grains with unusual Si isotopic ratios, including one C grain, 16 X grains, 1 Y grain, 5 Z grains, and 2 X-type Si{sub 3}N{sub 4} grains were selected for N, S, Mg-Al, and Ca-Ti isotopic analysis. The C grain is highly enriched in {sup 29}Si and {sup 30}Si (δ{sup 29}Si = 1345‰ ± 19‰, δ{sup 30}Si = 1272‰ ± 19‰). It has a huge {sup 32}S excess, larger than any seen before, and larger than that predicted for the Si/S supernova (SN) zone, providing evidence against the elemental fractionation model by Hoppe et al. Two SN models investigated here present a more satisfying explanation in terms of a radiogenic origin of {sup 32}S from the decay of short-lived {sup 32}Si (τ{sub 1/2} = 153 yr). Silicon-32 as well as {sup 29}Simore » and {sup 30}Si can be produced in SNe by short neutron bursts; evidence for initial {sup 44}Ti (τ{sub 1/2} = 60 yr) in the C grain is additional evidence for an SN origin. The X grains have marginal {sup 32}S excesses, much smaller than expected from their large {sup 28}Si excesses. Similarly, the Y and Z grains do not show the S-isotopic anomalies expected from their large Si isotopic anomalies. Low intrinsic S contents and contamination with isotopically normal S are the most likely explanations.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002 (China)
  2. Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO 63130 (United States)
  3. Dipartimento di Fisica, Università di Torino, I-10125 Torino (Italy)
  4. Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Vic 3800 (Australia)
  5. Department of Physics, University of Basel, CH-4056 Basel (Switzerland)
  6. Key Laboratory of Earth's Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 (China)
Publication Date:
OSTI Identifier:
22364361
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 799; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ASTROPHYSICS; ELEMENT ABUNDANCE; INTERSTELLAR GRAINS; ISOTOPE RATIO; METEORITES; NUCLEOSYNTHESIS; SILICON 28; SILICON 29; SILICON 30; SILICON 32; SILICON CARBIDES; SILICON NITRIDES; SULFUR 32; SUPERNOVAE; TITANIUM 44