This paper summarizes the isoscaling and isospin related studies in asymmetry nuclear reactions by different dynamic and sta tistical models. Isospin dependent quantum molecular dynamics model (IQMD) and lattice gas model (LGM) are used to study the isoscaling properties and isoscaling parameters dependence on incident energies, impact parameters, temperature and other parameters. In the LGM model, the signal of phase transition has been found in free neutron (proton) chemical potential dif ference Δμn or Δμp as a function of temperature, or in free neutron and proton chemical potential difference Δμn-Δμp. Density dependence of symmetry energy coefficient Csym(ρ/ρ0) is also studied in the frame of LGM, with the potential parameters which can reproduce the nuclear ground state property, soft density dependence of symmetry energy is deduced from the sim ulation results. Giant dipole resonance (GDR) induced by isospin asymmetry in entrance channel is also studied via IQMD model, and the dynamic dipole resonance shows isospin sensitivity on the isospin asymmetry of entrance channel and sym metry energy of the nuclear equation of state (EOS). GDR can also be regarded as a possible isospin sensitive signature.
TIAN WenDong1, MA YuGang1, CAI XiangZhou1, FANG DeQing1, WANG HongWei1 & WU HongLi1,2 1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
We present a systematic analysis of two-pion interferometry for the central Au＋Au collisions at √SNN=3, 5, 7, 11, 17, 27, 39, 62, 130 and 200 GeV/c with the help of a multiphase transport （AMPT） model. Emission source-size radius parameters Rlong, Rout, Rside and the chaotic parameter A are extracted and compared with the experimental data. Transverse momentum and azimuthal angle dependencies of the HBT radii are also discussed for central Au＋Au collisions at 200 GeV/c. The results show that the HBT radii in central collisions do not change much above 7 GeV/c. For central collisions at 200 GeV/c, the radii decrease with the increasing of transverse momentum PT but are not sensitive to the azimuthal angle. These results provide a theoretical reference for the energy scan program of the RHIC-STAR experiment.
Shear viscosity (η) is a basic transport coefficient of the medium.In this work,we calculate shear viscosity to entropy density ratio (η/S) of an equilibrated system in intermediate energy heavy ion collisions within the framework of the Boltzmann-Uehling-Uhlenbeck model (BUU) model.After the equilibration of Au + Au system at central collision in a fixed volume is reached,temperature,pressure and energy density are extracted by the phase space information and then η/S is calculated using the Green-Kubo formulas.The results show that η/S drops with the incident energy and its value is not so drastically different from the RHIC results.
How the initial fluctuation affects on the elliptic flow is investigated by investigating the rapidity, transverse 4-velocity, centrality dependencies of elliptic flow for Au+Au at 1 GeV/A with the help of an Isospin Quantum Molecular Dynamics (IQMD). In addition, we compare the flow calculated with respect to participant plane created by the initial geometry in coordinate space with the flow reconstructed by the experimental event-plane method, and compare the flow with the experimental data of the FOPI collaboration. It shows that there exists some discrepancy between the flows reconstructed by the above two methods.
WANG JiaMA YugangZHANG GuoqiangFANG DeqingHAN LixinSHEN Wenqing
Isospin-dependent Quantum Molecular Dynamics model (IQMD) has been applied to investigate the Pygmy Dipole Resonance (PDR) and Giant Dipole Resonance (GDR) in Ni isotopes by Coulomb excitation. By Gaussian fitting to the photon emission spectra, the peak energies and strengths of PDR and GDR are extracted. Their sensitivities to impact parameter, incident energy and the symmetry energy are discussed. By the comparison of energy-weighted sum rule (EWSR) with the data and other calculations for 68 Ni, the parameters of density-dependence of symmetry energy in the IQMD are constrained. In addition, the N/Z dependence of PDR and GDR parameters of Ni isotopes are investigated, and the results that the EWSR increases linearly with the N/Z are obtained.
TAO ChengMA YugangZHANG GuoqiangCAO XiguangFANG DeqingWANG Hongwei
Dynamical dipole mode in heavy-ion collisions has been studied by using an isospin-dependent BoltzmannUehling-Uhlenbeck(IBUU) model. We investigate the dependence of centroid energy and strength of the γspectrum on beam energy, N/Z ratio and mass asymmetry. The calculated yield and angular distribution of theγ-ray produced by dynamical dipole emission are consistent with the experimental data. The results show that the detailed study of dynamical dipole radiation can provide information on the isospin evolution of chargeasymmetric heavy-ion collisions around the normal nuclear density.
By extending the minimum spanning tree(MST)clusterization algorithm for the binding energy cut,the isospin asymmetry dependence of directed flow for isospin sensitive isobar pairs(neutrons-protons,3H-3He) is studied from low towards high incident energies.The modified clusterization method(MSTB) has the advantage to identify the fragments at quite early time.It enhances(reduces) the production of free nucleons(fragments) over MST method.The directed flow of isobaric pair3H-3He is more sensitive towards isospin asymmetry caused by MSTB than isobaric pair n-p.This sensitivity becomes quite strong towards the high incident energy and neutron-rich reaction system.In conclusion,the inclusion of binding energy in clusterization method for the flow studies has been uniquely important for understanding the isospin physics,especially for high density behavior of symmetry energy.
The shear viscosity （7） and entropy density （s） are studied for the central Au＋Au collisions with the help of a microscopic transport model, namely the isospin-dependent quantum molecular dynamic model （IQMD）. Employ the formula given in Ref. [1],η is calculated as a time dependent variable for different incident energies from 40 MeV/u to 120 MeV/u and the energy dependence of η/s of nuclear matter in the most compressed stage in collision process is displayed.
The correlation between neutron-to-proton yield ratio （Rnp） and neutron skin thickness （δnp） in neutron-rich projectile induced reactions is investigated within the framework of the Isospin-Dependent Quantum Molecular Dynamics （IQMD） model. The density distribution of the Droplet model is embedded in the initialization of the neutron and proton densities in the present IQMD model. By adjusting the diffuseness parameter of neutron density in the Droplet model for the projectile, the relationship between the neutron skin thickness and the corresponding Rnp is obtained. The results show strong linear correlation between Rnp and δnp for neutron-rich Ca and Ni isotopes. It is suggested that Rnp may be used as an experimental observable to extract δnp for neutron-rich nuclei, which is very interesting in the study of the nuclear structure of exotic nuclei, the equation of state （EOS） of asymmetric nuclear matter and neutron-rich matter in astrophysics, etc.
Molten salt reactor(MSR) is a potential nuclear power reactor of Generation Ⅳ.The working process of the primary loop of an MSR is studied in this paper.A physical model is established to describe the coupled heat transfer for the MSR core channels,the temperature negative feedback and the neutron characteristics.The simulation code,NDPID,has been developed with the object-oriented method,conducting the neutron diffusion and transient analysis in a parallel way.The simulation data and diagrams of neutron,power,flow rate and temperature can be obtained via graphical user interface.The simulation results can be used for further study on MSRs of larger dimensions and more complicated geometry.
