| dc.description.abstract | The development of a unified approach in nuclear theory, which starts from bare nucleon-nucleon and multi-nucleon forces and makes accurate predictions on the structure of atomic nuclei is a major goal of modern nuclear physics. A truly breakneck speed of theoretical advances in this area during the last three decades, coupled with modern computational techniques and hardware, has produced an array of new theoretical models, capable of making robust ab initio predictions for nuclear systems with an ever-growing number of nucleons. Comprehensive and multifaceted experimental tests of these models are indispensable. Light exotic nuclei are particularly important for these tests due to a combination of several factors. Ab initio calculations are more manageable for light nuclei (few nucleons). Exotic nuclei by definition have an imbalance between protons and neutrons, adding an isospin dimension to the tests. Small (or negative) binding energies of exotic nuclei make the effects of the continuum more important even for the lowest or ground states, adding yet another important factor to the model tests. Finally, exotic nuclei are known to often have unusual structures with experimentally observed or observable signatures, such as neutron halos, and we expect the ab initio models to reproduce these new features.
A method of studying the structure of exotic, neutron-rich nuclei by populating the correspond-ing isobaric analogue states in less exotic isobaric partners is discussed in this thesis. It is bench-marked for the relatively well studied case of 9Li, and then applied to study the exotic, neutron unbound nucleus 13Be. The isobaric analogue states are populated in proton resonant scattering with radioactive beams using the so called Thick Target Inverse Kinematics method [1]. The T=3/2 excited states in 9Be (isobaric analogues of 9Li) were populated with 8Li + p scattering using the RESOLUT radioactive nuclear beam facility [2] at Florida State University. R-matrix calculations [3] were performed to describe the excitation function for the p+8Li resonance elastic scattering using already known states in the T=3/2, A=9 isobaric system [4, 5]. This benchmark study demonstrated that the isobaric analogue (T=3/2) states indeed dominate the p+8Li excitation function at low (with respect to the T=3/2, A=9 ground state) excitation energies and that reliable spectroscopic information, such as spin-parities and partial widths for these states, can be extracted. The new T=3/2, Jπ=5/2+ state in 9Be at 18.5 MeV was observed for the first time, confirming the onset excitation energy of 4 MeV for the 2s1/2 shell in the T=3/2, A=9 isobaric multiplet, which was recently observed for the first time in 9C [5]. The results of this study are published in Ref. [6].
The Structure of the neutron unbound nucleus 13Be was studied through T=5/2 isobaric analog states in 13B, populated in proton resonant scattering on 12Be. Previously structure of 13Be has been extensively studied experimentally [7, 8, 9, 10, 11, 12, 13, 14] and theoretically [15, 16, 17, 18, 19, 20] but no consensus has been achieved on the structure of the ground state and other low-laying states of this exotic nucleus. The radioactive beam, 12Be, for this experiment was produced by the TRIUMF ISAC II rare isotope beams facility. The excitation function for p+12Be is shown to be dominated by T=5/2 resonances. The R-matrix analysis indicates that the experimental data can be described by two T=5/2 resonances in 13B with spin-parities 1/2+ and 5/2+. These new data provide strong evidence that the ground state of 13Be has spin-parity of Jπ = 1/2+, resolving the long-standing puzzle of the structure of 13Be. | |
