Characterisation of the first 1/2+ excited state in 9B and isospin symmetry breaking studies in A = 9 nuclei

Abstract

The 9Be - 9B isospin doublet carries fundamental significance for both nuclear structure and nuclear astrophysics studies. The first excited 1/2+ state in 9Be is already well established. However, its isobaric analogue 1/2+ state in 9B has not been unambigously determined yet. Theoretically, two popular descriptions of the 9Bnucleus either use a cluster model with two unbound alpha particles held together by a covalent proton or using the shell model, as a 8Be core + proton in the sd shell. An experimental determination of the excitation energy of the first 1/2+ state in 9B will provide valuable information in validating the theoretical model that adequately describes such light unbound nuclei. Further, it will also provide a robust test of mirror (isospin) symmetry violations via measurements of mirror energy differences in the doublet. Although there have been several experimental attempts to characterize the first 1/2+ state in 9B several discrepancies still exist in reported values of the excitation energies. This thesis describes an experiment performed at iThemba LABS using the 9Be(3He,t)9B reaction to address the above issue. As a byproduct, the thesis also describes an additional determination of the excitation energy of the second J-pi = 1/2+, T = 3/2 state in 9B from the same experiment. This was performed in order to resolve a discrepancy related to the excitation energy of this state. The consequence of this measurement related to Isobaric Multiplet Mass Equation (IMME) for the excited T = 3/2, A = 9 quartet is discussed briefly.