Direct Measurements of Nuclear Reactions in Hot Stellar Environments

Abstract

Understanding the origins of intermediate mass nuclei requires accurate knowledge of nuclear reaction rates. This thesis addresses two projects targeting measurements of nuclear cross sections relevant in hot astrophysical environments. Direct measurements of neutron capture on 67Zn and 68Zn were performed using the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center (LANSCE). A new 68Zn(n,&gamma) cross section in the neutron energy range from 150 eV to 850 keV and Maxwellian-Averaged Cross Sections from 20 keV-100 keV are presented along with the details of the analysis. These reaction rates are important for the weak s process that takes place in massive stars and is responsible for the production of a major portion of the elements from mass 60 < A < 90. A technical component of this thesis pertains to the development of the LSU-FSU Array for Nuclear Astrophysics and Structure with Exotic Nuclei (ANASEN). This advanced detector technology will be used to perform direct (and indirect) measurements of charged particle nuclear reactions on proton-rich nuclei using radioactive ion beams. Reactions on proton-rich nuclei impact the abundances of intermediate mass nuclei produced in core-collapse supernova and have a substantial impact on understanding observations of Type I X-Ray bursts, the most common stellar explosion. Specifically, we developed an approach using ANASEN for direct measurements of (&alpha,p) reactions that have a significant influence on Type I X- Ray bursts. The results from a 14N(&alpha, p) proof-of-principle test, and progress with direct measurements of (&alpha,p) reactions with the ANASEN active gas target are reported.