Radiative alpha capture on S34 at astrophysically relevant energies and design of a scattering chamber for high precision elastic scattering measurements for the DRAGON experiment

Abstract

Radiative α capture on ³⁴S has been shown to have an impact on nucleosynthesis in hot and explosive astrophysical environments, including stellar (core and shell) oxygen burning, Type II supernovae, and Type Ia supernovae. However, there exist discrepancies in the literature for the resonance strengths of two strong resonances within the Gamow window for oxygen burning temperatures (which ranges from ECM = 2.286 - 4.080 MeV at 2.2 GK). Previous measurements suffered from systematic uncertainties inherent in the experimental technique employed. Furthermore, there are several states in ³⁸Ar lying within the Gamow window for oxygen burning temperatures which no ³⁴S + α resonance strength/energy measurements have been performed. The strengths of these resonances could significantly impact the astrophysical reaction rate at oxygen burning temperatures. The present measurement was performed in inverse kinematics at the DRAGON electromagnetic mass separator. DRAGON's experimental technique allows direct measurement of quantities such as stopping power and resonance energy, alleviating the need for external inputs and reducing uncertainty in many cases. The results of the present measurement agree well with existing Hauser-Feshbach statistical models of the astrophysical reaction rate for ³⁴S (α,γ) ³⁸Ar in the temperature range of interest. Additionally, in order to increase the science reach of the DRAGON experiment, within this thesis a new type of scattering chamber was designed to allow for the high precision measurement of charged particle elastic scattering cross sections in inverse kinematics with radioactive beams. The chamber was designed and fabricated at CSM and for the first time tested in beam.