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Fusion of Heavy-Ions at Energies Near the Conlomb Barrier.

Christley, James Alan. (1992) Fusion of Heavy-Ions at Energies Near the Conlomb Barrier. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

Fusion of heavy-ions at energies near the Coulomb barrier is studied. The coupled channels method is used to investigate the effect of channel couplings on fusion observables. The results of a comprehensive coupled channels analysis of 16O + 208Pb are interpreted in an one-channel model using effective optical potentials. The fusion component of the potentials is l-dependent and absorbs flux under the Coulomb barrier, indicating that fusion can be initiated by coupling to non-elastic direct reaction channels before penetrating the barrier. Coulomb excitation is an important process in heavy-ion reactions. Conventional coupled channels integration methods are inefficient for long-range Coulomb coupling. We implement a coupled channels version of the piecewise analytic method which can be included in existing coupled channels codes and which considerably shortens the computing time for Coulomb excitation calculations. The fusion observables are derived for the general density matrix describing scattering of a polarised beam from an aligned target. In the derivation the total cross section is evaluated using the generalised optical theorem. In the most general case, the fusion cross section is sensitive to off-diagonal elements of the incident density matrix. Fusion of 16O with an aligned 165Ho target is studied. In particular we study the effect of alignment on fusion. Coupled channels, semi-classical and eigenchan-nels calculations are compared. All three methods give similar unpolarised fusion cross sections but the semi-classical method predicts a larger orientation dependence. Ambiguities in the definition of the deformed potentials are discussed. We make predictions for the fusion observables in an experiment, and compare our predictions with earlier estimates. We predict that aligning the target will change an unpolarised cross section of order 10 mb by between 40% and 175%, dependent on the choice of alignment axis.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Christley, James Alan.
Date : 1992
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 1992.
Depositing User : EPrints Services
Date Deposited : 30 Apr 2019 08:08
Last Modified : 20 Aug 2019 15:32
URI: http://epubs.surrey.ac.uk/id/eprint/851401

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