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Title: Barium isotopic composition of mainstream silicon carbides from Murchison: Constraints for s-process nucleosynthesis in asymptotic giant branch stars

We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ({sup 138}Ba/{sup 136}Ba) values are found, down to –400‰, which can only be modeled with a flatter {sup 13}C profile within the {sup 13}C pocket than is normally used. The dependence of δ({sup 138}Ba/{sup 136}Ba) predictions on the distribution of {sup 13}C within the pocket in asymptotic giant branch (AGB) models allows us to probe the {sup 13}C profile within the {sup 13}C pocket and the pocket mass in AGB stars. In addition, we provide constraints on the {sup 22}Ne(α, n){sup 25}Mg rate in the stellar temperature regime relevant to AGB stars, based on δ({sup 134}Ba/{sup 136}Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative δ({sup 134}Ba/{sup 136}Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process (i process), which is activated by the very late thermal pulse during the post-AGB phase and characterized by a neutron density much higher than the s process. Thesemore » two grains may have condensed around post-AGB stars. Finally, we report abundances of two p-process isotopes, {sup 130}Ba and {sup 132}Ba, in single SiC grains. These isotopes are destroyed in the s process in AGB stars. By comparing their abundances with respect to that of {sup 135}Ba, we conclude that there is no measurable decay of {sup 135}Cs (t {sub 1/2} = 2.3 Ma) to {sup 135}Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before {sup 135}Cs decayed.« less
Authors:
; ; ;  [1] ;  [2] ; ;  [3] ; ;  [4] ;  [5] ;  [6] ;  [7] ;  [8]
  1. Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637 (United States)
  2. Chicago Center for Cosmochemistry, Chicago, IL 60637 (United States)
  3. Dipartimento di Fisica, Università di Torino, I-10125 Torino (Italy)
  4. INAF–Osservatorio Astronomico di Collurania, via Maggini snc, I-64100 Teramo (Italy)
  5. Laboratory for Space Sciences, Washington University, St. Louis, MO 63130 (United States)
  6. Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States)
  7. Department of Physics, University of Basel, Basel CH-4056 (Switzerland)
  8. Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada)
Publication Date:
OSTI Identifier:
22356999
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 786; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ALPHA REACTIONS; BARIUM ISOTOPES; CAPTURE; CARBON 13; CESIUM 135; DISTRIBUTION; DUSTS; GIANT STARS; INTERMEDIATE NEUTRONS; ISOTOPE RATIO; MAGNESIUM 25; NEON 22 TARGET; NEUTRON DENSITY; NEUTRON EMISSION; NUCLEOSYNTHESIS; S PROCESS; SILICON CARBIDES; STARS