Silicon Burning and the Formation of the Iron Peak Nuclei

Details Silicon Burning and the Formation of the Iron Peak Nuclei Silicon Burning and the Formation of the Iron Peak Nuclei

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........19h&link_type=abstract

Thesis (PH.D.)--HARVARD UNIVERSITY, 1995.Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6794.

Statistics

Computation

8

Supernovae, Stars

Scientific paper

At its heart, this thesis is a study of silicon burning, the ultimate stage of nuclear energy generation in massive stars (those with masses greater than 8 times the mass of the sun) and a major contributor to the thermonuclear energy liberated by exploding supernovae. As such it is the source of the iron peak elements found in nature. With the conversion of silicon to iron taking place via a series of photodisintegrations and proton, neutron, and alpha-particle captures, silicon burning is inherently the most complicated of the nuclear burning stages. It is therefore an extremely computationally intensive process. We show that this process is further complicated because Coulomb screening of nuclear reactions plays an important role in the process of silicon burning, most importantly in the equilibrium abundances which result. Screening is also a consideration in the calculation of quasi-equilibrium abundances. Quasi-equilibrium (QSE), due to the near balance of opposing pairs of reactions during silicon burning, is an important tool to understanding the process of silicon burning. We find that the physics of silicon burning is dominated by the formation of 2 quasi-equilibrium groups, one centered on silicon and the other containing the iron peak elements. We further find that the degree of neutronization has a profound effect on quasi-equilibrium. For larger degrees of neutronization the QSE groups remain separate to much greater degrees of silicon exhaustion. Furthermore, the degree of neutronization is important in determining the membership of the quasi-equilibrium groups, the reaction fluxes which link these groups, and the rate of silicon exhaustion. We utilize the concept of quasi-equilibrium, to develop a new approximation for calculating the nuclear abundance distribution during silicon burning. The speed and accuracy of this quasi-equilibrium approximation allows us to discuss a method for studying the temporal evolution of silicon burning without resorting to computationally intensive full nuclear network calculations. Such a method is useful for investigating silicon burning in its hydrodynamic settings.

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