Study of Resonances in Light Nuclei for Nuclear Structure and Nuclear Astrophysics

Doctoral Dissertation
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Abstract

Resonances in exotic nuclei play a central role in the nucleosynthesis processes occurring in the stars. Nuclear reactions proceed through resonance states in exotic nuclei. This dissertation reports on measurements of resonances in 18Ne, 30S and 9Be.

The radioactive nucleus 18Ne was studied via the 16O(3He,n) reaction. These resonances are relevant in understanding one of the two breakout paths from the Hot Carbon-Oxygen-Nitrogen (HCNO) cycle. Neutrons from this reaction were measured in coincidence with charged particles from the decay of resonances in 18Ne to directly extract the charged particle branching ratios of the populated resonance states. Significant α branching ratios coming from the resonances at Eex = 7.95 MeV and Eex = 8.09 MeV were measured for the first time. Evidence of an exotic 2p decay is indicated from the state at Eex$ = 6.15 MeV. The results from this work allows for a more reliable calculation of the 14O(α,p)17F reaction rate, central in the breakout of the HCNO cycle and in the direct competition between α αp-process and the rp-process for the flow of nuclear material in the proton rich side of the valley of stability.

The exotic nucleus 30S was studied via the 28Si 3He,n transfer reaction. Neutrons from this reaction were measured in coincidence with charged particle decays from the populated resonance states in 30S. Several states above Eex = 8.5 MeV are reported for the first time. For the states measured between the proton decay threshold and the alpha decay threshold, the branching ratios were extracted and used to tentatively assign spins and parities. The results led to the determination of the first experimental 26Si (α,p)29P reaction rate. The calculated reaction rate is compared with statistical methods traditionally used in the calculations of such reaction rate. The results of the present work will be combined with the results of the 32S(p,t) experiment carried out by O'Brien.

Resonance states with Isospin T = 3/2 in 9Be were studied by bombarding a C2H4 target with radioactive 8Li beam using the hybrid Thick/Thin Target in Inverse Kinematics approach.

The elastic and inelastic excitation function of 8Li+p were measured in the energy region of 1.0 to 2.8 MeV in the center-of-momentum system. The population of T = 3/2 states in 9Be was confirmed. The parameters of the resonances observed 5/2- and 3/2- correspond to the expected values based on the knowledge of the structure of 9C and 9Li. No Isospin violating channels were necessary to reproduce the 8Li+p excitation function which validates the assumption that the T = ½ states are suppressed due to the multiple open neutron decay channels into the T = 0 states in 8Be. These results will be used to test predictions of ab-initio calculations made for A = 9 nuclei. The results will also be compared with Continuum Shell Model calculations. A firmer foundation to the method employed in this work to study neutron rich nuclei by populating isobaric analog states in resonance proton scattering experiments using neutron rich exotic beams is also supported by the present results.

Attributes

Attribute NameValues
URN
  • etd-11072011-124941

Author Sergio Jesus Almaraz Calderon
Advisor Ani Aprahamian
Contributor Michael Wiescher, Committee Member
Contributor Michael Hildreth, Committee Member
Contributor Ani Aprahamian, Committee Chair
Contributor Xiao-Dong Tang, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Physics
Degree Name PhD
Defense Date
  • 2011-09-20

Submission Date 2011-11-07
Country
  • United States of America

Subject
  • radioactive beams

  • nuclear physics

  • nuclear reactions

  • nuclear astrophysics

Publisher
  • University of Notre Dame

Language
  • English

Record Visibility and Access Public
Content License
  • All rights reserved

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