Abstract
Studying the nucleosynthesis in explosive astrophysical events is crucial for understanding the origin of the elements in our solar system and the nature of nuclear matter. This thesis work focuses on key reactions in the two most common explosive stellar phenomena: classical novae and X-ray bursts.
Classical novae are expected to play a role in enriching the abundance of light mass nuclei in the Universe. Therefore, the nuclear processes that drive classical novae need to be understood to understand the observed elemental abundances. If the origin of presolar grains can be determined to be from classical novae, these represent a key observable since they carry information on the isotopic abundances. It is thought that the origin of grains could be determined using their 34S/32S isotopic ratio. However, the expected abundance of 34S in the ejecta remains poorly constrained due to the uncertainty in the 34g,mCl(p,γ)35Ar reaction rate. In this work, a γ-ray spectroscopy study of 35Ar was carried out using Gammasphere and the Fragment Mass Analyzer at Argonne National Laboratory with the aim of identifying the key resonances that govern these astrophysical reaction rates. Spin-parity restrictions were made based on the observed decay branches and comparison with the mirror nucleus (35Cl), which allows the contribution to the reaction rate from each measured resonance to be determined.
Nucleosynthesis in X-ray bursts is driven by the rp-process. However, the breakout from the HCNO cycles into the rp-process is not fully understood. One proposed mechanism is the 15O(α,γ)19Ne reaction. The rate of this reaction needs to be calculated to determine if this is a plausible breakout reaction. Therefore, a new experimental setup named BlueSTEAl was developed at the Cyclotron Institute, Texas A&M to study the key 19Ne states via the 21Ne(p,t)19Ne reaction in inverse kinematics. BlueSTEAl consists of a stack of Si detectors to detect the light reaction products and a new focal plane system consisting of two parallel plate avalanche counters and a phoswich detector. Results are presented showing the particle identification capabilities of the focal plane detector. Unfortunately, issues with the Si detectors meant that the reaction rate could not be determined. However, had the Si detectors worked as expected, it is believed this would prove a promising method for determining the reaction rate.