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Study of Proton Emission in Complex Nuclei

Adolfsson, Jonatan LU (2016) PHYM01 20152
Mathematical Physics
Department of Physics
Abstract
In a recent experiment, the partial half-life (t1/2) of proton emission from the Iπ = 19/2- state of 53Co was accurately measured. A previous estimate is t1/2 ~ 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 J in 53Co is coupled to J = 6 for the neutrons, and J = 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... (More)
In a recent experiment, the partial half-life (t1/2) of proton emission from the Iπ = 19/2- state of 53Co was accurately measured. A previous estimate is t1/2 ~ 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 J in 53Co is coupled to J = 6 for the neutrons, and J = 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 53Co 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 53Co, 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 t1/2 by ~ 1.4. Next, nuclear deformation was included, and both proton and neutron overlaps were computed for different deformations β2 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 = 3 to = 9 was estimated to add a factor of ~ 3∙106 to the decay time, and the = 9 components of the proton wave function another factor of ~ 4∙108 - 7∙109. 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. (Less)
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author
Adolfsson, Jonatan LU
supervisor
organization
course
PHYM01 20152
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Nuclear physics, Nuclear theory, Nuclei far from stability, Proton decay, Cobalt-53
report number
Lund-mPh-16/01
language
English
id
8851250
date added to LUP
2016-05-11 12:52:35
date last changed
2016-05-30 08:57:35
@misc{8851250,
  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.},
  author       = {Adolfsson, Jonatan},
  keyword      = {Nuclear physics,Nuclear theory,Nuclei far from stability,Proton decay,Cobalt-53},
  language     = {eng},
  note         = {Student Paper},
  title        = {Study of Proton Emission in Complex Nuclei},
  year         = {2016},
}