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Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt........17l&link_type=abstract
Thesis (PhD). CLEMSON UNIVERSITY, Source DAI-B 61/06, p. 3093, Dec 2000, 66 pages.
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Scientific paper
This thesis presents models in an effort to explore the following two questions. How can we reconcile the abundances of the short-lived radioactivities in the early solar system, and what is the origin of the peculiar silicon isotopic anomalies in the mainstream presolar SiC grains? First, the production of short-lived radioactivities by energetic-particle irradiations is addressed. I find that conclusions that this scenario is ruled out because of results from simple, constant particle flux models are premature. I here describe different conclusions based on the time dependence expected in some models of particle irradiation. The energetic-particle scenario is still an open possibility. Second, an essential conundrum is that the short-lived r- process radioactivities had lower abundance in the early solar system than one would have expected from steady- state Galactic r-process nucleosynthesis, but that 182 Hf is about right for the steady-state expectations with realistic ISM mixing timescales. Based on the inhomogeneous GCE code I built, I study some implications of the short-lived r-process radioactivities in the early solar system. The results show that explaining the abundances of the short-lived r-process radioactivities simply by diverse r-process supernovae occurring on different timescales can work, but that in such a solution our solar system would probably have very different ratios of extinct radioactivities than others in our Galaxy. Third, chemical evolution models with an IMF changing with time can explain the slope 4/3 correlation line in the silicon three-isotope plot for the presolar mainstream SiC grains. The particular models I have run require that the contribution of the highest-mass supernovae increase with time in the Galaxy's history.
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