Coulomb breakup of halo nuclei by a time-dependent techniques

 

by

 

Pierre Capel

pierre.capel@centraliens.net
Service de Physique Quantique, Faculté des Sciences Appliquées, Université Libre de
Bruxelles (Brussels, Belgium)

SUPERVISOR:

Daniel Baye, Université Libre de Bruxelles (Brussels, Belgium)

COMMITTEE:

Robert Beauwens, Université Libre de Bruxelles (Brussels, Belgium) (Chair)

Michel Godefroid, Université Libre de Bruxelles (Brussels, Belgium)

Christiane Leclercq-Willain, Université Libre de Bruxelles (Brussels, Belgium)

Francis Michel, Université de Mons-Hainaut (Mons, Belgium)

Ian Thompson, University of Surrey (Guildford, UK)

Bruxelles, Jan 2004

 

Abstract

Halo nuclei are among the strangest nuclear structures.  They are viewed as a core containing most of the nucleons surrounded by one or two loosely bound nucleons.  These have a high probability of presence at a large distance from the core. Therefore, they constitute a sort of halo surrounding the other nucleons.  The core, remaining almost unperturbed by the presence of the halo is seen as a usual nucleus.

The Coulomb breakup reaction is one of the most useful tools to study these nuclei. It corresponds to the dissociation of the halo from the core during a collision with a heavy (high Z) target. In order to correctly extract information about the structure of these nuclei from experimental cross sections, an accurate theoretical description of this mechanism is necessary.

 

In this work, we present a theoretical method for studying the Coulomb breakup of one-nucleon halo nuclei.  This method is based on a semiclassical approximation in which the projectile is assumed to follow a classical trajectory.  In this approximation, the projectile is seen as evolving in a time-varying potential simulating its interaction with the target.  This leads to the resolution of a time-dependent Schrödinger equation for the projectile wave function.

The halo nucleus is described with a two-body structure: a pointlike nucleon linked to a pointlike core by a local potential. The idea of our method is to expand the projectile wave function on a three-dimensional spherical mesh.  With this mesh, the representation of the time-dependent potential is fully diagonal. It also leads to a simple representation of the Hamiltonian modelling the halo nucleus.  This expansion is used to derive an accurate evolution algorithm.

With this method, we study the Coulomb breakup of three nuclei: 11Be, 15C and  8B.  11Be is the best known one-neutron halo nucleus.  The good agreement between our calculations and recent experimental data suggests that it can be seen as a s1/2 neutron loosely bound to a 10Be core in its 0+ ground state. 15C is a candidate one-neutron halo nucleus.  The results of our model are in good agreement with the preliminary experimental data. It seems therefore that 15C can be seen as a 14C core in its 0+ ground state surrounded by a s1/2 neutron.  We have also used our method to study the Coulomb breakup of the candidate one-proton halo nucleus 8B.  Unfortunately, no quantitative agreement could be obtained between our results and the experimental data.  This is due to an inaccuracy in the treatment of the results of our calculations. Accordingly, no conclusion can be drawn about the pertinence of the two-body model of 8B.

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