[Show abstract][Hide abstract] ABSTRACT: In this proceeding we report on alpha particle emission through the nuclear break-up in the reaction 40Ca on a 40Ca target at 50A MeV. It is observed that alpha particles are emitted to the continuum with very specific angular distribution during the reaction. The alpha particle properties seem to be compatible with an alpha cluster in the daughter nucleus that is perturbed by the short range nuclear attraction of the collision partner and emitted as described by a time-dependent theory. This mechanism offers new possibilities to study alpha particle properties in the nuclear medium.
International Journal of Modern Physics E 05/2012; 20(04). · 0.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study pairing vibrations in 18,20,22O and 42,44,46Ca nuclei solving the time-dependent Hartree-Fock-Bogoliubov equation in coordinate space with spherical symmetry. We use the SLy4 Skyrme functional in the particle-hole part of the energy density functional and a local, density-dependent pairing functional in its particle-particle (hole-hole) part. Pairing vibrations are excited by a two-neutrons transfer operator. The Fourier analysis of the time-dependent response of the expectation value of this operator in the linear regime is used to extract strength functions. The presence of the giant pairing vibration is discussed.
International Journal of Modern Physics E 01/2012; 18(10). · 0.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We discuss pairing vibrations in the context of Time-Dependent Energy-Density-Functional formalism. The focus is put on the pairing part of the energy functional. We found that the density-dependence of the pairing functional impacts 2-nucleons transfer strengths.
Modern Physics Letters A 11/2011; 25(21n23). · 1.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this Rapid Communication, we report on α-particle emission through the nuclear breakup in the reaction 40Ca on a 40Ca target at 50 A MeV. It is observed that, similar to nucleons, α particles can be emitted to the continuum with very specific angular distribution during the reaction. The α-particle properties seem to be compatible with an α cluster in the daughter nucleus that is perturbed and is emitted by the short-range nuclear attraction of the collision partner. A time-dependent theory that describes the α-particle wave-function evolution is able to qualitatively reproduce the observed angular distribution. This mechanism offers new possibilities for studying α-particle properties in the nuclear medium.
Physical Review C 09/2010; 82(3). · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new Fermionic Molecular Dynamics (FMD) model based on a Skyrme functional is proposed in this paper. After introducing the basic formalism, an application to nuclear thermodynamics is presented.
[Show abstract][Hide abstract] ABSTRACT: We study the couplings between collective vibrations such as the isovector giant dipole and isoscalar giant quadrupole resonances in tin isotopes in the framework of the time-dependent Hartree-Fock theory with a Skyrme energy density functional. These couplings are a source of anharmonicity in the multiphonon spectrum. In particular, the residual interaction is known to couple the isovector giant dipole resonance with the isoscalar giant quadrupole resonance built on top of it, inducing a nonlinear evolution of the quadrupole moment after a dipole boost. This coupling also affects the dipole motion in a nucleus with a static or dynamical deformation induced by a quadrupole constraint or boost, respectively. Three methods associated with these different manifestations of the coupling are proposed to extract the corresponding matrix elements of the residual interaction. Numerical applications of the different methods to 132Sn are in good agreement with each other. Finally, several tin isotopes are considered to investigate the role of isospin and mass number on this coupling. A simple 1/A dependence of the residual matrix elements is found with no noticeable contribution from the isospin. This result is interpreted within the Goldhaber-Teller model.
Physical Review C 09/2009; 80(6). · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study the pygmy resonances in Sn isotopes within a microscopic multiphonon approach which has been successfully applied to heavy ion reactions in recent years. In the energy region of the pygmy resonances there are a few low lying multiphonon states. The question is whether they may contribute to the observed peak. Calculations show that the inelastic cross sections in the relevant energy region have a conisderable increase depending on the isotope and on the kind of Skyrme force used.
Journal of Physics Conference Series 06/2009; 168(1):012014.
[Show abstract][Hide abstract] ABSTRACT: We study, within a semiclassical coupled-channels approach, the possible effects of anharmonicities and non linearities on the excitation of the so-called pygmy resonances in several Sn isotopes and using two different Skyrme interactions. In the energy region of the pygmy resonances, there are a few low-lying multiphonon states. The question is whether they may contribute to the observed peak. Calculations show that the inelastic cross sections in the relevant energy region have an increase that varies from 3% to 21% depending on the isotope and on the kind of Skyrme force used. At the same time, we have studied the nature of the pygmy resonance state by means of a new criterion to establish whether this state can be considered as a collective one.
Physical Review C 05/2009; 79(5). · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present various properties of nuclear and compact-star matter, comparing the predictions from two kinds of phenomenological approaches: relativistic models (with both constant and density-dependent couplings) and nonrelativistic Skyrme-type interactions. We mainly focus on the liquid-gas instabilities that occur at subsaturation densities, leading to the decomposition of the homogeneous matter into a clusterized phase. Such study is related to the description of neutron-star crust (at zero temperature) and supernova dynamics (at finite temperature).
Physical Review C 11/2008; 78(5). · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The nuclear-matter liquid–gas phase transition induces instabilities against finite-size density fluctuations. This has implications for both heavy-ion-collision and compact-star physics. In this paper, we study the clusterization properties of nuclear matter in a scenario of spinodal decomposition, comparing three different approaches: the quantal RPA, its semi-classical limit (Vlasov method), and a hydrodynamical framework. The predictions related to clusterization are qualitatively in good agreement varying the approach and the nuclear interaction. Nevertheless, it is shown that (i) the quantum effects reduce the instability zone, and disfavor short-wavelength fluctuations; (ii) large differences appear between the two semi-classical approaches, which correspond respectively to a collisionless (Vlasov) and local equilibrium description (hydrodynamics); (iii) the isospin-distillation effect is stronger in the local equilibrium framework; (iv) important variations between the predicted time-scales of cluster formation appear near the borders of the instability region.
[Show abstract][Hide abstract] ABSTRACT: We address nuclear liquid-gas instablitities in the mean-field framework, using a Skyrme-like density functional. These instabilities lead to the clusterization of nuclear and compact-star matter at sub-saturation density. In this contribution, we study the extension of the spinodal region, how it affects star matter at beta-equilibrium and how it is affected by the choice of different Skyrme forces. The dynamics of cluster formation is also characterized, comparing a semi-classical approach to a quantal one.
[Show abstract][Hide abstract] ABSTRACT: We present a new method to introduce phase-space fluctuations in transport theories, corresponding to a full implementation of the Boltzmann–Langevin equation for fermionic systems. It is based on the procedure originally developed by Bauer et al. for transport codes employing the test particle method. In the new procedure, the Pauli principle is carefully checked, leading to a good reproduction of the correct fluctuations in the “continuum limit” (h→0). Accurate tests are carried out in one and two dimensional idealized systems, and finally results for a full 3D application are shown. We stress the reliability of this method, which can be easily plugged into existing transport codes using test particles, and its general applicability to systems characterized by instabilities, like for instance multifragmentation processes.
[Show abstract][Hide abstract] ABSTRACT: We discuss fragmentation mechanisms and isospin transport occurring in central collisions between neutron rich systems at Fermi energies. In particular, isospin effects are analyzed looking at the correlations between fragment isotopic content and kinematical properties. Simulations are based on an approximate solution of the Boltzmann-Langevin (BL) equation. An attempt to solve the complete BL equation, by introducing full fluctuations in phase space is also discussed.
[Show abstract][Hide abstract] ABSTRACT: (abridged) In this paper, we present the issues we consider as essential as
far as the statistical mechanics of finite systems is concerned. In particular,
we emphasis our present understanding of phase transitions in the framework of
information theory. Information theory provides a thermodynamically-consistent
treatment of finite, open, transient and expanding systems which are difficult
problems in approaches using standard statistical ensembles. As an example, we
analyze is the problem of boundary conditions, which in the framework of
information theory must also be treated statistically. We recall that out of
the thermodynamical limit the different ensembles are not equivalent and in
particular they may lead to dramatically different equation of states, in the
region of a first order phase transition. We recall the recent progresses
achieved in the understanding of first-order phase transition in finite
systems: the equivalence between the Yang-Lee theorem and the occurrence of
bimodalities in the intensive ensemble and the presence of inverted curvatures
of the thermodynamic potential of the associated extensive ensemble.
[Show abstract][Hide abstract] ABSTRACT: The equilibration of macroscopic degrees of freedom during the fusion of heavy nuclei, such as the charge and the shape, are studied in the time-dependent Hartree-Fock theory. The preequilibrium giant dipole resonance (GDR) is used to probe the fusion path. It is shown that such an isovector collective state is excited in N/Z asymmetric fusion and to a lesser extent in mass asymmetric systems. The characteristics of this GDR, such as its deformation, rotation, and vibration, are governed by the structure of the fused system in its preequilibrium phase. In particular, we show that a loweringq of the preequilibrium GDR energy is expected as compared to the statistical one. Revisiting experimental data, we extract evidence of this lowering for the first time. We also quantify the fusion-evaporation enhancement resulting from γ-ray emission from the preequilibrium GDR. This cooling mechanism along the fusion path may be suitable for synthesizing in the future superheavy elements using radioactive beams with strong N/Z asymmetries in the entrance channel.
Physical Review C 08/2007; 76(2). · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An imaginary potential associated with the inelastic excitation of the nuclei is computed in a multiphonon excitation model based on the random phase approximation. The surface properties of this potential are found to be dominated by giant-resonance degrees of freedom.
[Show abstract][Hide abstract] ABSTRACT: In the present work we take the non relativistic limit of relativistic models and compare the obtained functionals with the usual Skyrme parametrization. Relativistic models with both constant couplings and with density dependent couplings are considered. While some models present very good results already at the lowest order in the density, models with non-linear terms only reproduce the energy functional if higher order terms are taken into account in the expansion.
[Show abstract][Hide abstract] ABSTRACT: By constructing an Ising analogue of compact-star matter at subsaturation density we explored the effect of Coulomb frustration on the nuclear liquid-gas phase transition. Our conclusion is twofold. First, the range of temperatures where inhomogeneous phases form expands with increasing Coulomb-field strength. Second, within the approximation of uniform electron distribution, the limiting point upon which the phase-coexistence region ends does not exhibit any critical behavior. Possible astrophysics consequences and thermodynamical connections are discussed.
[Show abstract][Hide abstract] ABSTRACT: Because of the presence of a liquid-gas phase transition in nuclear matter, compact-star matter can present a region of instability against the formation of clusters. We investigate this phase separation in a matter composed of neutrons, protons and electrons, within a Skyrme–Lyon mean-field approach. Matter instability and phase properties are characterized through the study of the free-energy curvature. The effect of β-equilibrium is also analyzed in detail, and we show that the opacity to neutrinos has an influence on the presence of clusterized matter in finite-temperature proto-neutron stars.