Dispersive contribution to the nucleus-nucleus potential

With a simple parametrization of the empirical imaginary potential depths, the real potential induced by a dispersion relation is calculated analytically for the elastic scattering of O16 by several target nuclei. Between 25e50 % of the real potential empirical depths can be attributed to this dispersive contribution when the energy approaches the Coulomb barrier. Thus, the anomaly observed in the microscopically calculated real potential at these energies can be explained by taking into account the real part induced from the imaginary one through the dispersion relation.Comisión Asesora de Investigación Científica y Técnica 2868-8

Nuclear-structure dependence of the fusion cross section for heavy ions

The energy dependence of the fusion cross section and its maximum value are well predicted, for a wide range of nuclei and energies, by introducing information on the nuclear matter density distribution into a simple formul

Simple estimates of excitation energy sharing between heavy and light fragments in heavy-ion reactions

Qualitative arguments are used to estiamte the ratio of excitation energies between heavy and light fragments for asymmetric heavy-ion collisions. The value of this quantity is linked to the relative role played by inelastic and transfer degrees of freedom and thereby to an approximate function of the total kinetic energy loss. A numerical analysis that confirms the trends anticipated by the simple arguments is performed for the reactions 56Fe+ 238U and 86Kr+ 208Pb at bombarding energies in the laboratory of 476 and 1565 MeV, respectivelyComisión Asesora de Investigación Científica y Técnica 2868-8

A phenomenological imaginary part of the optical potential for heavy ions

The depth of the imaginary part of the optical potential is derived from the assumption that, at a given energy and for each partial wave L, it is proportional to the compound nucleus density level up to a given excitation energy above the yrast level corresponding to the angular momentum L, and remains a constant for smaller values of L. The prescription is successfully tested for the system 16O + 28Si at nine different projectile energies between 33 and 81 MeV; it fails however at 141.5 MeV, as expected, because other channels, besides elastic scattering and fusion, are important

Dynamic effective potential for α-particle bound and quasibound states

We exploit analytic properties of the optical potential for elastic scattering of α particles on nuclei to extract information on the effective interaction that should be used to describe the motion of a cluster of two neutrons and two protons bound to a nuclear system. This prescription solves long-standing ambiguities in the formalisms used for the study of α decay.EU Human Capital and Mobility program ERBCHRX-CT92-007CICYT PB92-066

Double folding with a density-dependent effective interaction and its analytical approximation

The real part of the optical potential for heavy ion elastic scattering is obtained by double folding of the nuclear densities with a density-dependent nucleon-nucleon effective interaction which was successful in describing the binding, size, and nucleon separation energies in spherical nuclei. A simple analytical form is found to differ from the resulting potential considerably less than 1% all through the important region. This analytical potential is used so that only few points of the folding need to be computed. With an imaginary part of the Woods-Saxon type, this potential predicts the elastic scattering angular distribution in very good agreement with experimental data, and little renormalization (unity in most cases) is needed. NUCLEAR REACTIONS Optical model for nucleus-nucleus, double folding model, nucleon-nucleon effective interactio

Refractive or diffractive interpretation of heavy-ion elastic scattering

A characteristic pattern frequently observed in the angular distribution of heavy-ion elastic scattering at moderate energies above the Coulomb barrier has been attributed either to a Fresnel diffraction or to a rainbow effect. We propose a comparison between the strong absorption radius Rsa and the rainbow radius Rr at different energies, which may have some relevance on deciding whether the absorptive or the refractive interpretation is to be preferred. Despite the difficulties in the exact determination of these two distances, an analytical expression for their energy dependence is found empirically by analyzing data of fifteen pairs of heavy ions. According to this criterion the center-of-mass energy, above which refraction prevails over absorption, is proportional to Z1Z2. NUCLEAR SCATTERING Optical and diffraction models, rainbow refraction of heavy ions

Analytical expressions for the dispersive contributions to the nucleon-nucleus optical potential

Analytical solutions of dispersion relations in the nucleon-nucleus optical model have been found for both volume and surface potentials. For the energy dependence a standard Brown-Rho function has been assumed for both the volume and surface imaginary contributions multiplied in this later case by a decreasing exponential function. The solutions are valid for any even value of the powers appearing in these functional forms.Junta de Andalucía y CICYT FPA2001-0144-C05-03 FPA2001-4960-EUnión Europea KIW-CT-2000-0010

Critical radii for alpha-particle elastic scattering

The critical radii obtained from analyses of the elastic scattering of alpha-particles by a range of nuclei are found to be closely connected with the nuclear matter distributions obtained by summing the squares of single-particle wavefunctions. This provides a method of calculating the details of the optical potentials from the structure of the target nucleus

Polarization effects due to coupling of elastic to compound states

From a compound nucleus level-density-dependent imaginary potential an energy-and angular-momentum-dependent polarization potential is obtained by using the dispersion relation. The effect of coupling in this way the compound nucleus states to the elastic channel is to introduce a strongly attractive real polarization potential at small separation of the centers of mass of the colliding nuclei. The effective potential at distances around the strong absorption radii of the systems 16O+24Mg, 28Si, 40Ca at different energies above the barrier is very slightly modified. Thus, the elastic and fusion cross sections of these reactions are hardly affected by the polarization potential