Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.........4v&link_type=abstract
Thesis (PHD). UNIVERSITY OF NOTRE DAME , Source DAI-B 59/02, p. 712, Aug 1998, 123 pages.
Astronomy and Astrophysics
Astrophysics
Nucleosynthesis, Gamma Widths, Proton Widths, Chlorine, Argon
Scientific paper
Recent observations indicate considerable overabundances of Si and S in nova ejecta relative to solar matter. These observations may be explained by an enrichment process in an established SiP cycle where material cannot be processed towards higher masses. Escape out of this cycle is possible via the 31P(p,γ )32S reaction. The proton capture reaction, however, competes with the (p,α ) reaction and the outcome depends on the temperature and density conditions of the stellar environment. This work focuses in establishing the temperature and density conditions for which the 31S(p,γ )32Cl reaction may provide an alternative breakout out of the SiP cycle. Since the direct investigation of this reaction was not possible, the proton unbound levels were populated via the 32S(3He,t)32Cl reaction and the tritons were observed both directly and in coincidence with the γ de-excitation of the levels of interest. The excitation energies of the levels between 1.1 and 2.3 MeV have been determined and resonance parameters have been assigned to the levels with astrophysical importance. The astrophysical implications of the new information are discussed and the role of the 31S(p,γ )35Cl reaction as a possible escape out of the SiP cycle is established. In addition, the reaction 34(p,γ )35Ar has been investigated via the study of the 36Ar(3He,α)35Ar reaction. The 34Cl(p,γ )35Ar reaction appears to play an important role in the nucleosynthesis helping material to advance to higher masses; establishing the dependence of its total reaction rate to the temperature and density conditions of the various astrophysical sites is therefore desirable. The excitation energies (up to 7 MeV) of the levels in $/sp[35]$Ar have been determined with significant improvement in the accuracy, especially for the levels above the proton threshold. These results will minimize the uncertainties in the calculation of the total reaction rate in a subsequent study. The determination of the resonance strengths, however, is beyond the scope of this work since the spin and parities of the levels of astrophysical importance are not known.
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