# Neutrinos in Core-Collapse Supernova Nucleosynthesis

## Abstract

The environment of supernova explosions is dominated like no other known scenario by neutrinos. In addition to their crucial role for initiating the explosion itself, neutrinos have an important impact on the production of chemical elements in supernovae. An extensive set of improved neutrino-induced reaction cross-sections is compiled, covering almost the whole nuclear chart. The majority of the cross-sections are calculated based on Random Phase Approximation (RPA) with single- and multi-particle evaporation channels based on statistical model codes. Individual cross-sections that are of particular importance, are derived from experimental data or dedicated shell model calculations, while previous results from the literature were also included.

With these cross-sections the $\nu$ process accompanying the explosive nucleosynthesis is studied with a one-dimensional supernova model based on progenitors of solar metallicity with initial main sequence masses between 13 and 30 solar masses. Modern supernova simulations find that neutrinos are less energetic than what was assumed in previous studies of the neutrino process. Using average neutrino energies compatible with modern simulations we investigate the production of 7Li, 11B, 19F, 138La and 180Ta and find reduced yields compared to previous studies assuming higher neutrino energies. As a result the yields of 11B, 138La and 180Ta are in agreement with their solar abundances, when contributions from other sources are to be taken into account. Implementing a set of neutrino-nucleus cross-sections that is complete in the sense that it includes reactions on all nuclei that are included in the nucleosynthesis calculations, allows to get an overview of the whole extend of process. As a results we can conclude that effects on stable nuclei that have not been discussed previously in the literature are limited to the order of 10%. Dependencies on stellar structure aspects are discussed in detail for the most relevant cases.

We also explore the impact of neutrino-nucleosynthesis on the production of the long-lived radioactive isotopes 22Na, 26Al and 36Cl. We find that the yield of 26Al is increased by a factor of 1.4 and 22Na is found to be efficiently produced in the Carbon-rich zones of some progenitors, providing a possible explanation for radiogenic 22Ne found in meteorites.

Furthermore, we show the importance of going beyond the standard description of supernova neutrino properties for nucleosynthesis by including the predictions of the neutrino signal from a sophisticated supernova simulation. This shows that the definition of an appropriately averaged neutrino temperature is difficult and underestimates the efficiency of the neutrino process because elevated neutrino energies for short periods of time are not appropriately captured. We also identify effects of the dynamics that have only minor consequences for the nucleosynthesis.

For the first time the neutrino process in the innermost supernova ejecta is addressed by using thermodynamic tracers from a two-dimensional supernova simulation. We conclude that the contribution of the alpha-rich freeze out to the production of the light elements B and Li is negligible in this model. However, we can confirm a substantial production of 138La and 180Ta in a self-consistent model. To investigate the production of 92Nb we also include its production in the neutrino-p process in the neutrino driven winds ejected from the hot proto-neutron star, including the effects of recently measured nuclear masses. We find that the production is also significantly affected by neutrino spallation reactions, in particular on 4He. With the contribution we find a 92Nb/93Nb ratio that is compatible with values found in primitive meteorites. Finally, an overview of the combined contribution of supernovae to the production of the elusive p-nuclei is given.

Item Type: Ph.D. Thesis
Erschienen: 2018
Creators: Sieverding, Andre
Title: Neutrinos in Core-Collapse Supernova Nucleosynthesis
Language: English
Abstract:

The environment of supernova explosions is dominated like no other known scenario by neutrinos. In addition to their crucial role for initiating the explosion itself, neutrinos have an important impact on the production of chemical elements in supernovae. An extensive set of improved neutrino-induced reaction cross-sections is compiled, covering almost the whole nuclear chart. The majority of the cross-sections are calculated based on Random Phase Approximation (RPA) with single- and multi-particle evaporation channels based on statistical model codes. Individual cross-sections that are of particular importance, are derived from experimental data or dedicated shell model calculations, while previous results from the literature were also included.

With these cross-sections the $\nu$ process accompanying the explosive nucleosynthesis is studied with a one-dimensional supernova model based on progenitors of solar metallicity with initial main sequence masses between 13 and 30 solar masses. Modern supernova simulations find that neutrinos are less energetic than what was assumed in previous studies of the neutrino process. Using average neutrino energies compatible with modern simulations we investigate the production of 7Li, 11B, 19F, 138La and 180Ta and find reduced yields compared to previous studies assuming higher neutrino energies. As a result the yields of 11B, 138La and 180Ta are in agreement with their solar abundances, when contributions from other sources are to be taken into account. Implementing a set of neutrino-nucleus cross-sections that is complete in the sense that it includes reactions on all nuclei that are included in the nucleosynthesis calculations, allows to get an overview of the whole extend of process. As a results we can conclude that effects on stable nuclei that have not been discussed previously in the literature are limited to the order of 10%. Dependencies on stellar structure aspects are discussed in detail for the most relevant cases.

We also explore the impact of neutrino-nucleosynthesis on the production of the long-lived radioactive isotopes 22Na, 26Al and 36Cl. We find that the yield of 26Al is increased by a factor of 1.4 and 22Na is found to be efficiently produced in the Carbon-rich zones of some progenitors, providing a possible explanation for radiogenic 22Ne found in meteorites.

Furthermore, we show the importance of going beyond the standard description of supernova neutrino properties for nucleosynthesis by including the predictions of the neutrino signal from a sophisticated supernova simulation. This shows that the definition of an appropriately averaged neutrino temperature is difficult and underestimates the efficiency of the neutrino process because elevated neutrino energies for short periods of time are not appropriately captured. We also identify effects of the dynamics that have only minor consequences for the nucleosynthesis.

For the first time the neutrino process in the innermost supernova ejecta is addressed by using thermodynamic tracers from a two-dimensional supernova simulation. We conclude that the contribution of the alpha-rich freeze out to the production of the light elements B and Li is negligible in this model. However, we can confirm a substantial production of 138La and 180Ta in a self-consistent model. To investigate the production of 92Nb we also include its production in the neutrino-p process in the neutrino driven winds ejected from the hot proto-neutron star, including the effects of recently measured nuclear masses. We find that the production is also significantly affected by neutrino spallation reactions, in particular on 4He. With the contribution we find a 92Nb/93Nb ratio that is compatible with values found in primitive meteorites. Finally, an overview of the combined contribution of supernovae to the production of the elusive p-nuclei is given.

Divisions: 05 Department of Physics
05 Department of Physics > Institute of Nuclear Physics
05 Department of Physics > Institute of Nuclear Physics > Theoretische Kernphysik
05 Department of Physics > Institute of Nuclear Physics > Theoretische Kernphysik > Theoretical Nuclear Astrophysics Group
Date Deposited: 05 Aug 2018 19:55