Coulomb breakup effects on the optical potentials of weakly bound nuclei

The optical potential of halo and weakly bound nuclei has a long range part due to the coupling to breakup that damps the elastic scattering angular distributions. In order to describe correctly the breakup channel in the case of scattering on a heavy target, core recoil effects have to be taken into account. We show here that core recoil and nuclear breakup of the valence nucleon can be consistently taken into account. A microscopic absorptive potential is obtained within a semiclassical approach and its characteristics can be understood in terms of the properties of the halo wave function and of the reaction mechanism. Results for the case of medium to high energy reactions are presented.Comment: 25 latex pages, 4 tables, 6 figures. Submitted to Nucl. Phys.

Reaction Mechanisms with Exotic Nuclei

This talk examines a number of reaction mechanisms for scattering initiated by an exotic projectile. Comparisons are made with recent experimental data, in order to extract information on the peculiarity of the nuclear structure under extreme conditions and to test the accuracy of the available theoretical methods. Predictions for future experiments are also made.Comment: 13 Latex pages, 2 table, 2 ps figures. Invited talk given at the Symposium on Nuclear Clusters, Rauischholzhausen, Germany, 5-9 August 200

Unbound exotic nuclei studied by transfer to the continuum reactions

In this paper we show that the theory of transfer reactions from bound to continuum states is well suited to extract structure information from data obtained by performing "spectroscopy in the continuum". The low energy unbound states of nuclei such as $^{10}$Li and $^{5}$He can be analyzed and the neutron-core interaction, necessary to describe the corresponding borromean nuclei $^{11}$Li and $^{6}$He can be determined in a semi-phenomenological way. An application to the study of $^{10}$Li is then discussed and it is shown that the scattering length for s-states at threshold can be obtained from the ratio of experimental and theoretical cross sections. The scattering single particle states of the system n+$^{9}$Li are obtained in a potential model. The corresponding S-matrix is used to calculate the transfer cross section as a function of the neutron continuum energy with respect to $^{9}$Li. Three different reactions are calculated $^{9}Li(d,p)^{10}Li$, $^{9}Li(^{9}Be,^{8}Be)^{10}Li$, $^{9}Li(^{13}C,^{12}C)^{10}Li$, to check the sensitivity of the results to the target used and in particular to the transfer matching conditions. Thus the sensitivity of the structure information extracted from experimental data on the reaction mechanism is assessed.Comment: 21 pages, 5 ps figures, accepted for publication on Nucl. Phys.

Status of art of reaction models for projectiles far from stability

This talk will review the status of art of nuclear and Coulomb breakup theories and their relation to optical models of elastic scattering of exotic projectiles. The effect of the final state interactions between the breakup particle and the core and target nuclei will be clarified and some typical numerical calculations for the relevant observables will be presented and compared to experimental data. Finally new results will be shown to demonstrate the feasibility of a novel type of experiment involving heavy projectiles far from stability on heavy targets.Comment: 10 pages, 4 figures. Proceedings of NN2007, Rio de Janeir

A non-perturbative approach to halo breakup

The theory of weakly bound cluster breakup, like halo nucleus breakup, needs an accurate treatment of the transitions from bound to continuum states induced by the nuclear and Coulomb potentials. When the transition probability is not very small, a non-perturbative framework might be necessary. Nuclear excitation dominates at small impact parameters whereas the Coulomb potential being long range acts over a larger impact parameter interval. In this article, we propose an effective breakup amplitude which meets a number of requirements necessary for an accurate quantitative description of the breakup reaction mechanism. Furthermore our treatment gives some insight on the interplay between time dependent perturbation theory and sudden approximation and it allows to include the nuclear and Coulomb potentials to all orders within an eikonal-like framework.Comment: 22 Latex pages, 1 table, 8 eps figures. Accepted for publication on Nucl. Phys.

Coulomb-Nuclear Coupling and Interference Effects in the Breakup of Halo Nuclei

Nuclear and Coulomb breakup of halo nuclei have been treated often as incoherent processes and structure information have been extracted from their study. The aim of this paper is to clarify whether interference effects and Coulomb-nuclear couplings are important and how they could modify the simple picture previously used. We calculate the neutron angular and energy distributions by using first order perturbation theory for the Coulomb amplitude and an eikonal approach for the nuclear breakup. This allows for a simple physical interpretation of the results which are mostly analytical. Our formalism includes the effect of the nuclear distortion of the neutron wave function on the Coulomb amplitude. This leads to a Coulomb-nuclear coupling term derived here for the first time which gives a small contribution for light targets but is of the same order of magnitude as nuclear breakup for heavy targets. The overall interference is constructive for light to medium targets and destructive for heavy targets. Thus it appears that Coulomb breakup experiments need to be analyzed with more accurate models than those used so far.Comment: 28 Latex pages, 2 tables, 2 eps figures, 5 ps figures. Accepted for publication in Nucl. Phys.

Comparison of Transfer-to-Continuum and Eikonal Models of Projectile Fragmentation Reactions

Spectroscopic properties of nuclei are accessible with projectile fragmentation reactions, but approximations made in the reaction theory can limit the accuracy of the determinations. We examine here two models that have rather different approximations for the nucleon wave function, the target interaction, and the treatment of the finite duration of the reaction. The nucleon-target interaction is treated differently in the eikonal and the transfer-to-continuum model, but the differences are more significant for light targets. We propose a new parameterization with that in mind. We also propose a new formula to calculate the amplitude that combines the better treatment of the wave function in the eikonal model with the better treatment of the target interaction in the transfer-to-continuum model.Comment: 21 pages, latex file including 3 tables. 5 figures. Submitted to Phys. Rev.