Abstract
Research within the field of nuclear astrophysics aims to gain a more detailed understanding of the nucleosynthesis of elements that is ongoing throughout the universe. A key component of this research is experimentally measuring individual contributions to this process from various stellar environments and the reaction processes that occur in those environments. From this information a detailed model of the chemical evolution of the galaxy can be created. Specifically, this work focuses on one nuclear reaction which plays a significant role in the progression of nucleosynthesis in explosive stellar environments: the 33Cl(p, γ)34Ar proton-capture reaction.
Nuclei with masses up to A ∼ 40 have been observed in ejecta from ONe novae outbursts.
Meanwhile, sensitivity studies have identified uncertainties relating to the 33Cl(p, γ)34Ar reaction to be a significant limiting factor for the construction of accurate models of nucleosynthesis in ONe novae. However, this reaction cannot be measured directly, due to the current limita tions in producing sufficiently intense radioactive 33Cl beams. In this work, therefore, a detailed γ-ray spectroscopy study of neutron-deficient 34Ar nuclei, produced via 12C(24Mg,2n)34Ar, was performed. Several technical innovations have made this study possible, including the use of the GRETINA γ-ray tracking array and the excellent channel selectivity afforded by the
Fragment Mass Analyser (FMA) at Argonne National Laboratory’s ATLAS Facility. From this study, a detailed level scheme for the 34Ar nucleus, for which previous experimental information is scarce, was constructed and compared to the mirror nucleus, 34S, and shell-model calcula tions. Particular interest was paid to low-spin states above the proton-emission threshold at Sp = 4663.9(4) keV. These states correspond to low-l resonant captures in the 33Cl(p,γ) proton capture reaction, which are expected to dominate the rate of the reaction over temperatures typical of ONe novae, ∼ 0.2 − 0.4 GK. Implications of these experimental results are assessed as input for classical ONe novae simulations. Finally, isotopic abundances from ONe novae ejecta, predicted by these simulations, result in a 33S/32S ratio that is distinctive compared to that from supernovae. These predicted abundances have been compared to isotopic ratios mea sured in presolar grains (microscopic grains of primordial stardust) identifying a single presolar grain candidate as being potentially consistent with classical nova origins. Hence, this provides support to the use of sulphur isotopic ratios as a diagnostic for presolar grains of nova origins.