A. Smerzi

Publications (10)0 Total impact

• Article: Damping of giant monopole resonances within a linearized Landau-Vlasov dynamics

  V. Abrosimov, M. Di Toro, A. Smerzi
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  ABSTRACT: Isoscalar monopole vibrations in spherical nuclei are studied within the Landau-Vlasov dynamics. Energy and strength of the giant monopole resonance (GMR) are well reproduced. The Landau damping of the monopole vibrations is analyzed. It is found that the local Fermi surface corresponding to the GMR is deformed. The collision integral is included within the relaxation time approximation. The found total width is too small to explain the observed one in heavy nuclei. Because the Landau damping is sensitive to the effective nuclear force the missing part of the width can be connected to certain properties of the latter.
  Zeitschrift für Physik A Hadrons and Nuclei 08/1994; 347(3):161-171.
• Article: Giant dipole emission as a probe of the entrance channel dynamics

  V. Baran, M. Colonna, M. Di Toro, A. Guarnera, A. Smerzi
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  ABSTRACT: In this article we focus on specific features associated with the giant dipole γ-ray emission from deformed long-living nuclear systems. Solving numerically the Vlasov equation, we follow the fusion path for entrance channels with different mass asymmetry in low-energy heavy-ion collisions, just above the fusion threshold. We observe the formation of long-living deformed compound nuclei in the more symmetric cases. We show that very important features, such as the energy and the angular correlation of the emitted γ's, are characteristic effects of the emission from such deformed systems. For charge-asymmetric channels we reveal the presence of a new “direct” dipole mode, related to the charge equilibration dynamics. From the interplay between charge and the shape equilibration time scales we can suggest new experiments to study the dipole propagation in excited nuclei.
  Nuclear Physics A.
• Article: The many facets of giant resonances at high excitation energies

  V. Baran, M. Colonna, M. Di Toro, A. Guarnera, V.N. Kondratyev, A. Smerzi
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  ABSTRACT: We show that from a study of collective motions built on highly excited states we can extract important information on open problems in nuclear structure and dynamics: 1.i)Competition between one- and two-body dissipation,2.ii) Effects of correlations and related density fluctuations,3.iii) Transition in the nature of nuclear collective motions: from pure quantum to classical sound waves,4.iv) Pre-equilibrium effects: the “dynamical” dipole in charge asymmetric entrance channels,5.v) Fusion hindrance from dynamical instabilities.We try also to discuss the relevance of new, more exclusive, experiments and of a larger systematics.
  Nuclear Physics A.
• Article: Searching for instabilities in nuclear dynamics

  M. Colonna, M. Di Toro, A. Guarnera, V. Latora, A. Smerzi
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  ABSTRACT: We present a general procedure to identify instability regions which lead to multifragmentation events in heavy ion collisions. The method covers all possible sources of dynamical instabilities. Information on the instability point, like the time when the nuclear system entters the critical region, the most unstable modes and the time constant of the exponential growing of the relative variances, are deduced without any numerical bias. Some hints towards a fully dynamical picture of fragmentation processes are finally suggested.
  Physics Letters B.
• Source

  Available from: M. Di Toro

  Article: Pre-equilibrium effects on properties of hot giant dipole resonances

  Ph. Chomaz, M. Di Toro, A Smerzi
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  ABSTRACT: In this article we analyse how the presence of a pre-equilibrium dipole strength can affect the properties of the giant dipole resonance (GDR) built on hot nuclei. We show that a little amount of GDR phonons still excited when the compound nucleus is formed will substantially modify the γ-decay from the giant resonance region. Also on the basis of microscopic calculations of the reaction dynamics we propose to study the effect of the N over Z ratio in the entrance channel. This analysis could bring independent information on the problem of the GDR disappearing at high excitation energy.
  Nuclear Physics A.
• Article: Quenching of photon decay in hot giant dipole resonances

  A. Smerzi, M. Di Toro, D.M. Brink
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  ABSTRACT: The quenching of photon decays in giant dipole resonances (GDR) at high excitation energy (E∗) is explained as due to the competition between γ-ray and particle emission. This effect is related to a large increase of the GDR width with the temperature of the nucleus in presence of a pre-equilibrium mechanism that also tends to reduce the collective dipole strength. A saturation of the GDR width at high excitation energy cannot account for the experimental data. Limiting temperatures for the observation of GDR γ-decays are deduced. The E∗-dependence of photon yields above the GDR region is also discussed.
  Physics Letters B.
• Article: Neck instabilities in deep inelastic collisions at medium energies

  M. Colonna, M. Di Toro, A. Guarnera, V. Latora, A. Smerzi, Zhong Jiquan
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  ABSTRACT: A novel reaction mechanism for semi-peripheral heavy ion collisions is discussed, due to new features of the nuclear dynamics in the overlapping region. In a very selected beam energy range, between 40 and 70 MeV/u, we see the onset of new neck instabilities coupled to an increasing amount of dynamical fluctuations. Expected consequences are a possibility of intermediate mass fragment emission from the neck region and large variances in the projectile-like and target-like observables.
  Nuclear Physics A.
• Article: Pre-equilibrium and temperature effects on the disappearing of Giant Dipole Resonances in highly excited nuclei

  A. Bonasera, M. Di Toro, A. Smerzi, D.M. Brink
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  ABSTRACT: We show that an increase of the GDR spreading width with excitation energy is expected on the basis of an interplay between one-body and collisional damping. In the Sn region the width reaches the value of the resonance energy at and the probability of giant photon emission becomes very small. Pre-equilibrium effects could however play an important role and new experiments with charge asymmetric entrance channels are suggested.
  Nuclear Physics A. 569:215-223.
• Article: Dynamics of a quantal system

  V.N. Kondratyev, A. Smerzi, A. Bonasera
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  ABSTRACT: The quantum corrections to the Vlasov equation are analysed in the framework of the Wigner representation. The method is applied to multipole vibration of nuclei and subbarrier heavy ion collisions. Using micro- and macroscopic models we demonstrate that quantum terms result in coherence effects for dipole and quadrupole giant resonances. Anomalous behaviour of protons transfer probability due to the Fermi surface deformation is predicted.
  Nuclear Physics A.
• Article: Equilibrium and nonequilibrium fluctuations of the one-body distribution function

  A. Bonasera, M. Colonna, M. Di Toro, F. Gulminelli, A. Smerzi
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  ABSTRACT: A general method to evaluate small-amplitude fluctuations of the semiclassical one-body Wigner function is presented both in the equilibrium and nonequilibrium framework. The correlation function of fluctuations is calculated as a time or ensemble average over the Boltzmann-Nordheim-Vlasov dynamics using the test-particle approach. We show a comparison with an analytical result from fluctuation theory in the equilibrium limit. In realistic heavy-ion collisions we compute mass variances in incomplete fusion reactions and widths of projectile-like fragment distributions in peripheral fragmentation events. In this case, together with fluctuations coming from scattering processes, mean-field fluctuations are automatically included.
  Nuclear Physics A.