Role of the continuum in reactions with weakly bound systems: A comparative study between the time evolution of a break-up wave function and its coupled-channel approximation

We exploit a model describing the breakup of weakly bound nuclei that can be used as a laboratory for testing different prescriptions that have been advanced in the literature to take into account the nearby presence of continuum states. In the model, we follow the evolution of a single-particle wave function in one dimension, initially bound by a Woods-Saxon type potential and then perturbed by a time- and position-dependent external field. Proper choices of this potential can simulate the effect of the interaction between reaction partners in a nuclear collision. These processes generate inelastic excitation probabilities that-distributed over the bound and continuum states of the system-lead to either a partial or a total fragmentation of the final wave function.Ministerio de Educación y Ciencia (España) y FEDER FIS2008-04189 FPA2006-13807-C02-01Programa Consolider Ingenio CSD2007-0042INFNJunta de Andalucía P07-FQM-02894 FQM16

Investigating the nucleus-nucleus potential at very short distances

Recent progress in experimental techniques have made possible accurate measurements of fusion cross sections far below the Coulomb barrier, revealing an unexpected behavior of these quantities as a function of the bombarding energy. Besides providing a plausible cause for the observed energy dependence we profit from the nature of this explanation and the high sensitivity of the experimental data to show how one can use these measurements to investigate the radial dependence of the nuclear ion-ion potential at extremely close distances

Treatment of continuum in nuclear reactions involving weakly bound systems. A simple model to test different prescriptions describing the coupling to continuum states.

We exploit a model describing the break-up of weakly-bound nuclei that can be used as a laboratory for testing different prescriptions that have been advanced in the literature to take into account the near-by presence of continuum states. In the model we follow the evolution of a single particle wave function in one dimension, initially bound by a Woods-Saxon type potential and then perturbed by a time- and position-dependent external field. Proper choices of this potential can simulate the effect of the interaction between reaction partners in a nuclear collision. These processes generate inelastic excitation probabilities that - distributed over the bound and continuum states of the system - lead to either a partial or a total fragmentation of the final wave function. The comparison with the exact calculations shows that standard coupled channel descriptions based on discretization of the continuum can be accurate only when a proper choice is made of the number of discrete states, of the energy mesh and of the energy cutoff. This may imply, even in simplified cases. the use of a rather large (and unpracticable) number of channels. The use of a more restricted number of channels may lead to misleading results

Macroscopic pairing vibrational model, self-consistent pairing coupling constant, and the fifth term of von Weizs ̈ acker’s semiempirical formula

The implementation of a number-conserving formalism for pair-addition and pair-removal modes has impaired the possibility of developing an intuitive and self-consistent picture for collective pairing modes. In this paper, we show how a relaxation of this constraint leads to a unified model with true predictive poweFEDER y Ministerio de Educación y Ciencia FIS2005-01105 FPA2005-0446

Relativistic Coulomb excitation of the giant dipole resonance in nuclei: A straightforward approach

We investigate alternatives to the standard formalism used for the study of relativistic Coulomb excitation of the giant dipole resonance in nuclei. The idea is to obtain reasonable results for the probabilities of excitation and cross sections to the one-phonon and two-phonon levels avoiding the substantial complexity of the treatments exploited so far. This is achieved for the relevant range of partial waves up to bombarding energies of at least 5 GeV per nucleon. The transfer of energy to the center of mass of the excited nuclei is also investigated

Relativistic Coulomb excitation of the giant dipole resonance in nuclei: How to calculate transition probabilities without invoking the Liénard-Wiechert relativistic scalar and vector potentials

The conclusions extracted from a recent study of the excitation of giant dipole resonances in nuclei at relativistic bombarding energies open the way for a further simplification of the problem. It consists in the elimination of the relativistic scalar and vector electromagnetic potentials and the familiar numerical difficulties associated with their presence in the calculation scheme. The inherent advantage of a reformulation of the problem of relativistic Coulomb excitation of giant dipole resonances along these lines is discussed.Ministerio de Educación y Ciencia IS2005-01105 FPA2005-0446

Semiclassical calculation of heavy-ion scattering in the chaotic regime

The semiclassical approach has proven to be a most valuable tool for the construction of the scattering matrix and accurate evaluation of cross sections in a large variety of heavy-ion collision problems. In its familiar implementation, however, its use is restricted to what is now known as the "regular regime", as it makes use of classical reaction functions that must be continuous and interpolable. In this paper we identify what version of the semiclassical formalisms may be especially suitable for extension into the chaotic regime that develops at energies close to the Coulomb barrier. We also show the crucial role of the absorptive part of the ion-ion potential to retain the usefulness of the semiclassical methods under conditions of irregularity.Ministerio de Educación y Ciencia FIS2005-01105 FPA2005-0446

Metrics Development for UML Tools evaluation

The Unified Modelling Language (UML) has become a defacto standard for software development practitioners. There are several tools that help the use of UML. Users of those tools must evaluate and compare different versions of the tools they intend to use or are using to assess the possibility of changing or acquiring one. There are several ways to perform this evaluation from the simple rule-of-thumb to numeric or quantitative methods. We present an ongoing project that evaluates UML tools using the Logic Scoring of Preference (LSP) method. This method is very briefly presented and also some of the ongoing work in building a model directed to UML tool evaluation is explained.Eje: Ingeniería en SoftwareRed de Universidades con Carreras en Informática (RedUNCI

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

Selective nuclear transparency induced by chaotic scattering

We investigate the effects of nuclear absorption on the population of intrinsic vibrational states in scattering processes involving heavy ions. It is found that at the classical level the removal of flux assumes a qualitatively different form in the regular or chaotic regimes. Specifically, it is shown how certain reaction channels turn out to be—in the latter case—relatively insensitive to the strength of the absorptive potential. This realization has a counterpart at the quantum level where, at the chaotic layer, conditions of selective transparency in the nuclear system are enforced.DFG Bo 1109/1CONYCET Pid. 3233/92EU Network Contract CHRX-CT92-0075Comisión Interministerial de Ciencia y Tecnología PB95-0533-