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Title: Theoretical nuclear physics
Author: Merchant, A. C.
ISNI:       0000 0001 3394 7688
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1979
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The states in the mass 18 and 19 nuclei which are strongly excited in three- and four-nucleon transfer reactions are considered. A cluster model employing a local effective interaction with the core and approximating the requirements of the Pauli principle with an orthogonality condition is used. We present a microscopic derivation of the effective cluster-core potentials for alpha cluster states in 18F and 19F based on the shell model approximations to the ground states of 14N and 15N respectively and an alpha-nucleon scattering potential. In 19F phenomenological and microscopic calculations yield essentially identical results. The predicted splitting of doublets is very small and mixing with non- cluster states is apparent in the experimental spectrum. In 18F a tensor force between cluster and core is predominantly responsible for the splitting of the observed triplets. Close agreement between phenomenological and microscopic treatments occurs again. However, the latter shows that mixing of states with differing orbital angular momenta by the tensor force is important. This leads to a re-examination of the experimental candidates for cluster states, which indicates that mixing with two-particle shell model states may be important. A similar microscopic treatment is developed for trinucleon cluster states in 18F and 18O but is hindered by the lack of information concerning the spin-dependent terms in the nucleon-trinucleon potential. Some of the forces between cluster and core are closely related, and the results are linked with phenomenology to see what sort of nucleon-trinucleon forces are needed to reproduce the observed spectrum. Finally, the effect of core polarization on the alpha spectrum in 18F is considered by mixing bands based on the ground state and excited 1+ states of 14N via the tensor force.
Supervisor: Buck, Brian ; Rowley, Neil Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nuclear physics ; Cluster theory (Nuclear physics)