出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Proton-rich material in a state of nuclear statistical equilibrium (NSE) is one of the least studied
regimes of nucleosynthesis. One reason for this is that after hydrogen burning, stellar evolution
proceeds at conditions of equal number of neutrons and protons or at a slight degree of neutron
richness. Proton-rich nucleosynthesis in stars tends to occur only when hydrogen-rich material
that accretes onto a white dwarf of neutron star explodes, or when neutrino interactions in the
winds from a nascent proto-neutron star or collapsar-disk drive the matter proton rich prior to or
during the nucleosynthesis. In this paper we solve the NSE equations for a range of proton-rich
thermodynamic conditions. We show that cold proton-rich NSE is qualitatively different from
neutron-rich NSE. Instead of being dominated by the iron-peak nuclei with the largest binding
energy per nucleon that have a proton to nucleon ratio close to the prescribed electron fraction,
NSE for proton-rich material near freeze-out temperature is mainly composed of 56Ni and free
protons. Previous results of nuclear reaction network calculations rely on this non-intuitive fact,
which this paper will explain. We show how the differences and especially the large fraction of
free protons arises as a direct result from the minimization of the Helmholtz free energy.
