Physics – Nuclear Physics
Scientific paper
Dec 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...226..984f&link_type=abstract
Astrophysical Journal, Part 1, vol. 226, Dec. 15, 1978, p. 984-995.
Physics
Nuclear Physics
25
Nuclear Astrophysics, Nuclear Fusion, Nuclei (Nuclear Physics), Stellar Interiors, Stellar Models, Stellar Structure, Atomic Excitations, Energy Storage, Gravitational Collapse, Heavy Nuclei, High Temperature, Iron, Nickel, Phase Shift, Resonance, Supernovae
Scientific paper
A nondivergent prescription for the calculation of nuclear partition functions at high temperature is derived. When this is expressed as an integral over nuclear level densities, particle-unstable states in the continuum contribute only if they correspond to increasing scattering phase shifts, so that the disappearance of narrow levels provides a natural energy cutoff and the partition functions saturate at temperatures approaching 1 trillion K. The decreasing phase shifts at higher energies lead to subtractions which would in the infinite temperature limit cancel the bound-state contributions exactly as demanded by Levinson's (1949) theorem. This prescription is applied to the numerical evaluation of high-temperature partition functions for Ni-56 and Fe-56, the sensitivity to various approximations is investigated, and a simple expression is proposed for application to nuclei with unknown parameters. Some astrophysical implications are discussed. In particular, storage of energy in the excited states of a nucleus is emphasized as an important effect during supernova core collapse.
Engelbrecht Chris A.
Fowler William A.
Woosley Stan E.
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