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Polarisation effects in the scattering of deformed heavy ions below the Coulomb barrier.

Roberts, Elved John. (1994) Polarisation effects in the scattering of deformed heavy ions below the Coulomb barrier. Doctoral thesis, University of Surrey (United Kingdom)..

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In this thesis predictions of polarisation observables are made for the elastic scattering of a quadrupole deformed spin 3/2 projectile from a spherical spinless target below the Coulomb barrier. Re-orientation to the ground state only is considered. For similar reactions at energies above the Coulomb barrier it is known that exact tidal symmetry allows for a simplification of the scattering problem which successfully gives predictions for polarisation observables. Exact tidal symmetry requires an interaction potential to be diagonal in tidal spin and treats the momentum dependent centrifugal barrier approximately through the iso-centrifugal approximation. In the present study the validity of the iso-centrifugal approximation below the Coulomb barrier is tested. Calculations are carried out using both classical and quantum mechanics and are found to be in close agreement with each other but fail to predict polarisation observables correctly, the iso-centrifugal approximation breaking down badly. In an attempt to understand why the iso-centrifugal approximation breaks down, a semi-classical method introduced by Sukumar and Brink is used. This method is based on a path integral formalism and a consistent quantum mechanical treatment of both the relative motion and internal degrees of freedom. Expressions for polarisation observables to first order in the projectile quadrupole moment are developed and evaluated. These expressions are compared to quantum mechanical coupled channels calculations and other approximate semi-classical calculations; good agreement is found. The results of the tidal symmetry calculations are reproduced through the Sukumar and Brink technique by using an approximate time evolution operator and considering only certain contributions to the scattering, in effect making the iso-centrifugal approximation. It is found that to correctly predict polarisation observables 'angular' contributions to the scattering cannot be ignored and the interplay between 'radial' and 'angular' contributions is discussed. The validity of the 'shape effect' relations, which are obtained as a direct consequence of tidal symmetry, is explored. The relations are obeyed well for backward angles but break down considerably for forward angles.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
Roberts, Elved John.
Date : 1994
Contributors :
Depositing User : EPrints Services
Date Deposited : 09 Nov 2017 12:14
Last Modified : 15 Mar 2018 19:45

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