Dissertation/Thesis Abstract

Weak Interactions of Hot Nuclei in Stellar Collapse
by Misch, Gordon Wendell, Ph.D., University of California, San Diego, 2014, 82; 3624869
Abstract (Summary)

The physics of the atomic nucleus and supernovas are fundamental to our very being. Indeed, supernovas provide the wind that disperses the nuclei of which we are composed, and the physics of nuclei is pivotal in supernova dynamics. During supernova core collapse, the extremely high temperatures and densities and low entropy favor large, neutron-rich nuclei at high excitation energy. My collaborators and I examine two weak interactions that occur in nuclei under these conditions. First, we study the production of neutrino pairs via de-excitation of hot nuclei. In de-exciting, the nucleus can emit a virtual Z0 boson that decays into a neutrino-antineutrino pair. We find this to be the dominant source of neutrino pairs of all flavors during collapse. Second, we use modern shell model computation techniques to revise the Brink-Axel hypothesis method of computing electron capture rates that was pioneered by Fuller, Fowler, and Newman. Our results show that the Brink-Axel hypothesis (which posits that the bulk of nuclear transition strength is distributed among transition energies independently of initial excitation energy) fails at low and moderate excitation, but that at high initial energies, the strength is largely independent of excitation. The failure of the Brink-Axel hypothesis manifests as the redistribution of strength to low and negative transition energies, which can have the effect of increasing the overall electron capture rate in the core.

Indexing (document details)
Advisor: Fuller, George
Commitee: Burgasser, Adam, Keres, Dusan, Marti, Kurt, Minster, Bernard
School: University of California, San Diego
Department: Physics
School Location: United States -- California
Source: DAI-B 75/10(E), Dissertation Abstracts International
Subjects: Astrophysics, Physics, Nuclear physics
Keywords: Brink hypothesis, Electron capture, Hot nuclei, Neutrino pair emission, Supernovas
Publication Number: 3624869
ISBN: 9781303990359
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