[en] Within a quantum molecular dynamics model we calculate the largest Lyapunov exponent (LLE), the density fluctuation, and the mass distribution of fragments for a series of nuclear systems at different initial temperatures. The LLE peaks are found at the temperature ('critical temperature') where the density fluctuation reaches a maximal value and the mass distribution fragments is fitted best by the Fisher's power law from which the critical exponents for mass and charge distribution are obtained. The time-dependent behavior of the LLE and density fluctuation is studied. The authors find that the time scale of the density fluctuation is much longer than that of inverse LLE, which means that chaotic motion can be developed well during the process of fragment formation. The finite-size effect on 'critical temperature' for nuclear systems ranging from calcium to superheavy nuclei is also studied. (authors)

[en] Based on the quantum molecular dynamics model, the dynamical behaviors of the Liquid-gas phase transition in nuclei are investigated. In order to explore the characters of the Liquid-gas phase transition in the vicinity of the 'critical point', the Maximum Lyapunov exponent (MLE) is employed and the method of calculation of the MLE is developed. The dependence of the mass distribution of fragments, density fluctuation and the MLE on temperature has been studied for nuclear systems ¹²⁴Sn and ²⁰⁸Pb. As the main results, the authors have found that for heavy nuclear systems the MLE and the density fluctuation reach the maximum values at the same temperature, in which the maximum liquid-gas coexistence region is also found from the mass distribution of fragments

[en] An investigation on the equation of state of the isospin asymmetric, hot, dense matter of nucleons and deltas is performed based on the relativistic mean field theory. The QHD-II-type effective Lagrangian extending to the delta degree of freedom is adopted. Our results show that the equation of state is softened due to the inclusion of the delta degree of freedom. The baryon resonance isomer may occur depending on the delta-meson coupling. The results show that the densities for appearing the baryon resonance isomer, the densities for starting softening the equation of state and the extent of the softening depend not only on the temperature, the coupling strengths but also the isospin asymmetry of the baryon matter. (authors)

[en] The elliptic flow for Z ≤ 2 particles in heavy ion collisions at energies from several tens to several hundreds MeV per nucleon is investigated by means of transport model,i.e. a new version of the Improved Quantum Molecular Dynamics model (ImQMD05), and compared with experiment results. By applying different Skyrme interactions in transport calculations we have studied the influence of nuclear equation of state(EOS) on the elliptic flow. We find a soft equation of state is required for elliptic flow in intermediate energy heavy ion collisions. The density and energy dependence of in-medium nucleon-nucleon cross sections(NNCS) are studied through the elliptic flow and the nuclear stopping in intermediate energy heavy ion collisions. At low energies, the behavior of in-medium NNCS is similar with phenomenological expression as well as the effective mass scaling, but at higher energies in-medium NNCS are enhanced compared with free ones

[en] An investigation on the equation of state of the isospin asymmetric, hot, dense matter of nucleons and deltas is performed based on the relativistic mean Geld theory. The QHD-Ⅱ-type effective Lagrangian extending to the delta degree of freedom is adopted. Our results show that the equation of state is softened due to the inclusion of the delta degree of freedom. The baryon resonance isomer may occur depending on the delta-meson coupling. The results show that the densities for appearing the baryon resonance isomer, the densities for starting softening the equation of state and the extent of the softening depend not only on the temperature, the coupling strengths but also the isospin asymmetry of the baryon matter. (authors)

[en] Some aspects of quantum chaos in a finite system had been studied based on the analysis of statistical behaviors of quantum spectra in heavy and superheavy nuclei. The dependence of the transition from order to chaos on nuclear deformation and nuclear rotation had been described. The influence of pairing effect on the statistical properties of spectra is also discussed. Some important experiment phenomena in nuclear physics had been understood from the point of view of interplay between order and chaos

[en] Based on the Improved Quantum Molecular Dynamics model (ImQMD), the difference of central collision in experiment and theory for low-intermediate energy heavy ion collisions is investigated. By analyzing the two kinds of central collisions, we find there is 50% difference on the charge distribution, and also on its average kinetic energy for heavier fragments, especially at the beam energy of 50 MeV/u. While, for the coalescence invariant neutron proton yield ratio, the calculations show there are about 5% ∼ 15% difference. Our results evidence that the impact parameter smearing effects must be considered for tightly constraining the nuclear equation of state and the in-medium nucleon-nucleon cross sections by heavy ion collision. (authors)

[en] The isospin effect in central and peripheral heavy-ion collisions at intermediate energies is studied by means of improved quantum molecular dynamics and isospin dependent quantum molecular model. It is shown that the influence of the density dependence of the symmetry potential on the average N/Z ratio of the products in central and peripheral reactions exhibits different character due to the different mechanism of particle emission. The authors find that the average N/Z ratio of emitted nucleons in neutron-rich heavy ion collisions is sensitive to the symmetry potential for both central and peripheral cases. Furthermore, for peripheral neutron-rich heavy ion collisions, the N/Z ratio of intermediate mass fragments is also sensitive to the density dependence of the symmetry potential, which provides us with a useful probe to the symmetry potential. (author)

[en] Nuclear symmetry energy plays an important role in the properties of nuclei and neutron stars. Since theoretical predictions of the density dependence of symmetry energy S(ρ) from microscopic nucleon-nucleon interactions show large uncertainties, especially in the region of suprasaturation density, constraining the density dependence of symmetry energy has become one of the main goals in nuclear physics and has stimulated many theoretical and experimental studies. In this paper, we have reviewed the ImQMD05 code and its description on charge distribution, collective flow and nuclear-nuclear stopping. By comparing ImQMD05 prediction with data, the isoscalar part of nucleonic mean field, the energy and density dependence of in-medium NN cross sectoin in the ImQMD05 were determined. In order to extracting the symmetry energy information by comparing the ImQMD05 calculations with the data for ^112,124Sn +^112,124 Sn at E_beam=50 MeV/u, the influence of symmetry potential and in-medium NN cross section on the isospin sensitive observables of intermediate-energy heavy-ion collisions was investigated. Focusing on the region above the Fermi energy, our results show that the symmetry potential plays a more important role in the experimental observables, such as double neutron to proton ratio and the isospin transport ratio Ri, than that the in-medium nucleon-nucleon cross section does. Since the copious production of intermediate mass fragments is a distinguishing feature of intermediate-energy heavy-ion collisions, we also examined the influence of cluster emission on the isospin transport ratio using different isospin tracers. The values of the isospin transport ratios with the tracer defined by the isospin asymmetry of the heaviest fragments with Z≥20 in the projectile region is greater than those obtained from projectile residues (emitting source). This phenomenon can be tested experimentally. By comparing the ImQMD05 predictions with the data for three observables, the self-consistent constraints on the symmetry energy at subsaturation density were obtained. (authors)

[en] we present the symmetry energies for nuclear matter at finite temperature calculated by means of the thermodynamics with Skyrme energy density functional. We also present the ImQMD05 model analysis of the experimental data for the double n/p ratio and the isospin diffusion data for ^112,124Sn+^112,124Sn and the consistent constraint on the density dependence of the potential symmetry energy is obtained.