Study of Proton Emission in Complex Nuclei

University essay from Lunds universitet/Matematisk fysik; Lunds universitet/Fysiska institutionen

Abstract: In a recent experiment, the partial half-life ([i]t[/i][sub]1/2[/sub]) of proton emission from the [i]I[/i][sup]π[/sup] = 19/2[sup]-[/sup] state of [sup]53[/sup]Co was accurately measured. A previous estimate is [i]t[/i][sub]1/2[/sub] ~ 17 s. The purpose of this thesis was to explain this decay and give a theoretical estimate for the dominating hindrance factors. The angular momentum [i]J[/i] in [sup]53[/sup]Co is coupled to [i]J[/i] = 6 for the neutrons, and [i]J[/i] = 7/2 for the protons. All of this is transferred to the emitted proton during the decay. In a first approach, the neutron part was ignored and spherical symmetry assumed. Three different methods to describe this decay were tested and compared. These methods were validated by comparing computed reference half-lives to Ref. 1 and [sup]53[/sup]Co half-life to results obtained from the computational code GAMOW (Ref. 2). Assuming this model, all of these methods were accurate, and a method based on probability flow was selected for further calculations. For [sup]53[/sup]Co, the computed half-life was ~ 17 orders of magnitude too low in the first approach. The method was improved by including the pairing interaction, giving an increase in [i]t[/i][sub]1/2[/sub] by ~ 1.4. Next, nuclear deformation was included, and both proton and neutron overlaps were computed for different deformations [i]β[/i][sub]2[/sub] of the mother nucleus, assuming axial symmetry. The proton overlap had only a minor effect on the decay time. The increase in angular momentum from [i]ℓ[/i] = 3 to [i]ℓ[/i] = 9 was estimated to add a factor of ~ 3∙10[sup]6[/sup] to the decay time, and the [i]ℓ[/i] = 9 components of the proton wave function another factor of ~ 4∙10[sup]8[/sup] - 7∙10[sup]9[/sup]. The remaining factor was conjectured to come from the neutron overlap, but in the model used, this was computed to be zero. This was expected to be resolved by extension to triaxial shapes.

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