Proton rich nuclear statistical equilibrium

Ivo Seitenzahl, Francis Timmes, Abel Marin-Laflèche, Edward Brown, Georgios Magkotsios, James Truran

Research output: Chapter in Book/Report/Conference proceedingConference contribution


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.

Original languageEnglish (US)
Title of host publicationProceedings of Science
StatePublished - 2008
Event10th Symposium on Nuclei in the Cosmos, NIC 2008 - Mackinac Island, MI, United States
Duration: Jul 27 2008Aug 1 2008


Other10th Symposium on Nuclei in the Cosmos, NIC 2008
Country/TerritoryUnited States
CityMackinac Island, MI

ASJC Scopus subject areas

  • General


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