E. F. Aguilera

Simultaneous χ2-analysis of near-barrier fusion and elastic scattering for the proton-halo system 8B + 58Ni using dynamical Woods–Saxon polarization potentials

Fusion radial potential barrier for the 8B + 58Ni system is determined from a simultaneous optical model analysis of elastic scattering angular distributions and fusion data. Besides the nuclear bare potential, dynamical energy-dependent Woods–Saxon polarization potentials, i.e. UF (volume) and UDR (surface), are used. UF is a potential that accounts for polarization effects emerging from couplings to the fusion channel and UDR for effects due to direct reaction absorption couplings. Each of these potentials is split into real and imaginary potentials. The detailed physical meaning of these two terms of the optical potential is investigated. The interpretation of the results of our calculations confirms that the proton-halo characteristics of 8B enhance the fusion cross-section.

Breakup threshold anomaly for the8B +58Ni system at near-Coulomb barrier energies

By using recent fusion cross section measurements for the system {sup 8}B + {sup 58}Ni, a simultaneous analysis of elastic scattering, fusion, and total reaction cross sections is performed for the weakly bound system {sup 8}B + {sup 58}Ni at energies close to the Coulomb barrier. The analysis is carried out with an optical potential with fusion and direct reaction parts (i.e., the nuclear polarization potential U is split into a volume part U{sub F}, which accounts for fusion reactions and a surface part U{sub DR}, responsible for direct reactions). The parameters of the Woods-Saxon potentials are determined by a {chi}{sup 2} analysis of the data. The presence of the threshold anomaly is investigated from the energy dependence of both the fusion and direct reaction parts of the polarization potential.

Optical model parallel description of elastic, fusion and breakup cross sections for systems with weakly bound projectiles

A brief description is presented of the results obtained in recent years for the simultaneous analysis of elastic and fusion cross section data of nuclear reactions for several nuclear systems with weakly bound and halo projectiles. The method used in this description, consists of simultaneously determine the parameters of fusion UF and direct reaction UDR polarization potentials of Woods-Saxon geometric shapes, that fit the elastic and fusion data. As a matter of fact, UFis an energy dependent potential, with real VF and imaginary WFcomponents, that is responsible for fusion reactions. Similarly, UDR is also energy dependent with real VDR and imaginary WDR parts, that accounts for direct reactions. A general finding for all the systems presented is that, the real and imaginary parts of the fusion potential and direct reaction potentials, are related by a dispersion relation and their energy dependence around and below the Coulomb barrier, show the so-called Breakup Threshold Anomaly. The effect of breakup reactions on fusion cross sections is studied by analyzing the separate effect of the absorption potential WDR and the fusion barrier rising produced by VDR.

Interaction spatial barrier distributions for the proton-halo system 8B+58Ni

Radial barrier distributions for the proton-halo system 8B+58Ni are obtained by the use of Woods-Saxon polarization potentials calculated from a fit to elastic scattering angular distribution data. The strength, diffuseness and reduced radii of the polarization potentials, besides fitting the data, are such that reproduce the barrier height and position as extracted from a Wongs fit to the universal behavior of reduced interaction cross sections for halo systems. It is found that, for the proton-halo system 8B+58Ni, the interaction barrier height VI and the interaction barrier radius RI result correspondingly lower and larger than the Coulomb nominal barrier height VB and barrier position RB as expected from Barrier Penetration Models and double folding density dependent interactions such as the S?o Paulo Potential. It is also shown that, the determined energy dependent polarization potentials, besides satisfying the dispersion relation, present a behavior consistent with the Breakup Threshold Anomaly. Keywords. Nuclear Reactions, weakly bound nuclei, threshold anomaly.

Effects of breakup couplings on {sup 8}B+{sup 58}Ni elastic scattering

We use the continuum discretized coupled channel (CDCC) method to investigate the effects of breakup coupling on {sup 8}B+{sup 58}Ni elastic scattering. We evaluate angular distributions at several collision energies and show that our theoretical results are in excellent agreement with the recent data of Aguilera et al.[Phys. Rev. C 79, 021601(R) (2009)]. We show that nuclear excitations of the target have a weak influence on the elastic angular distributions but that the inclusion of continuum-continuum couplings is essential to reproduce the data.

Threshold anomaly in the elastic scattering of {sup 6}He on {sup 209}Bi

The energy dependence of the optical potential for the elastic scattering of {sup 6}He on {sup 209}Bi at near and subbarrier energies is studied. Elastic angular distributions and the reaction cross section were simultaneously fitted by performing some modifications in the ECIS code. A phenomenological optical model potential with the Woods-Saxon form was used. There are signatures that the so-called breakup threshold anomaly (BTA) is present in this system having a halo projectile {sup 6}He, as it had been found earlier for systems involving stable weakly bound nuclei.