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Title: A theoretical study of alpha-particle scattering and reactions with heavy nuclei
Author: Rhoades-Brown, M. J.
ISNI:       0000 0001 3515 151X
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1977
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This thesis is concerned for the main part with the elastic scattering of a-particles on heavy nuclei and nuclear reactions in which an alpha particle is transferred. Various a-[208]Pb potentials are calculated microscopically using a single folding model in which the target nuclear density is constructed from shell model wavefunctions. Using these potentials it is shown that it is possible to reproduce elastic scattering data at medium energies. The problems of applying these potentials to more complex nuclear reactions is discussed. The alpha decay of various Polonium isotopes and the a-transfer reaction [208]Pb(O[16]C[12]) Po[212] are then analysed using perturbation theory. By expanding the initial A+4 system in a cluster model representation and taking the difference between the full Hamiltonian of the system and a model Hamiltonian as the perturbation which causes alpha decay it is shown that the inconsistencies which existed in previous theories had been greatly reduced. Applying this technique to the ground state decay of polonium isotopes as well as the decay of the 18[+] isomeric state [212m]Po it is shown that the a-Pb spectro-scopic factor is now much larger than the most complicated shell model calculations. This magnitude is confirmed in the analysis of the a-transfer reaction and leads to the conclusion that alpha decay and alpha transfer reactions can be considered, to a good approximation, as one step processes in which a real alpha particle in its ground state is transferred. From the a-decay formalism a new energy-life time relation is derived which fits the appropriate experimental data of even Polonium isotopes, a range covering fourteen orders of magnitude. The problem of antisymmetrisation for an alpha particle in orbit around [208]Pb is investigated using a modified Resonating Group Method. A formalism is developed for the non-local kernels which uses a local density approximation. It is shown that the one particle exchange component is the dominant term and that exchange effects are not very important in the analysis of a-decay and a-transfer reactions to heavy systems. The non-local interaction kernel between an alpha particle and [208]Pb is also examined and the expected dominant term is investigated. Further improvements to the theory presented is given together with possible suggestions for extensions of the work.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available