Studies of the nuclear structure of 12C and the astrophysical production of 23Na

Nuclear reactions can be used to study both the structure of the atomic nucleus, and to study the evolution of stars and the Universe. In this thesis two experiments are presented: one studying the astrophysical impact of the 23Na(a,p)26Mg reaction, and one studying the nuclear structure of 12C near the proton separation energy of 16 MeV. The 23Na(a,p)26Mg reaction is an important reaction affecting the abundances of 23Na and the radioisotope 26Al in massive stars. Before 2014 experimental and theoretical data on this reaction was of unknown uncertainty. A new direct measurement of the 23Na(a,p)26Mg reaction was performed at Aarhus University and with two other independent modern measurements of the 23Na(a,p)26Mg reaction a new combined experimental reaction rate has been calculated with an uncertainty of 30%, and the impact on 23Na and 26Al production has been modelled and the abundances constrained by this reaction. 12C is a light, stable, and well-studied nucleus with current research generally on clustering phenomena. It is therefore unusual that a narrow shell-model predicted state with spin-parity 0- has not been experimentally observed already. Excited states of 12C were populated via the 11B(3He,d)12C reaction at iThemba LABS in South Africa, and analysed through R-matrix theory. No 0- state was observed in the region predicted by the shell-model, but a likely 0- state has been identified above the proton separation energy, and a detailed analysis of its properties using R-matrix theory is presented.