Gh Liu

Hard-photon flow and photon-photon correlation in intermediate-energy heavy-ion collisions

Hard photons emitted from energetic heavy-ion collisions are very interesting since they do not experience nuclear interaction, and therefore they are useful to explore properties of nuclear matter. We investigated hard-photon production and its properties in intermediate-energy heavy-ion collisions with the help of the Blotzmann-Uehling-Ulenbeck model. Two components of hard photons are discussed: direct and thermal. The positive directed flow parameter and negative elliptic flow parameter of direct photons are demonstrated and they are anticorrelated to the flows of free protons. The dependencies of hard-photon production and anisotropic parameters on impact parameter, beam energy, nuclear equation of state, and symmetry energy are also discussed. Furthermore, we investigated the two-photon momentum correlation function, from which the space-time structure information of the photon source could be extracted, as well as the two-photon azimuthal correlation, which could provide another good method to determine the elliptic flow parameter v(2) of direct hard photons.

Scaling of anisotropy flows in intermediate energy heavy ion collisions

Anisotropic flows ( v 1 , v 2 and v 4 ) of light nuclear clusters are studied by a nucleonic transport model in intermediate energy heavy ion collisions. The number-of-nucleon scalings of the directed flow ( v 1 ) and elliptic flow ( v 2 ) are demonstrated for light nuclear clusters. Moreover, the ratios of v 4 / v 2 2 of nuclear clusters show a constant value of 1/2 regardless of the transverse momentum. The above phenomena can be understood by the coalescence mechanism in nucleonic level and are worthy to be explored in experiments.

Azimuthal asymmetry of direct photons in intermediate energy heavy-ion collisions

Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter F and elliptic asymmetry coefficient v(2), for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive F and negative v(2) of direct photons are illustrated and they seem to be anti-correlated to the corresponding free protons flow. (c) 2008 Elsevier B.V. All rights reserved.

Nucleon-nucleon momentum correlation function for light nuclei

Nucleon-nucleon momentum correlation function have been presented for nuclear reactions with neutron-rich or proton-rich projectiles using a nuclear transport theory, namely Isospin-Dependent Quantum Molecular Dynamics model. The relationship between the binding energy of projectiles and the strength of proton-neutron correlation function at small relative momentum has been explored, while proton-proton correlation function shows its sensitivity to the proton density distribution. Those results show that nucleon-nucleon correlation function is useful to reflect some features of the neutron- or proton-halo nuclei and therefore provide a potential tool for the studies of radioactive beam physics.

DYNAMICAL AND SEQUENTIAL DECAY EFFECTS ON ISOSCALING AND DENSITY DEPENDENCE OF THE SYMMETRY ENERGY

Isoscaling properties of the primary and final products are studied via isospin dependent quantum molecular dynamics (IQMD) model and the followed sequential decay model GEMINI, respectively. Both primary and final products isoscaling parameter α keeps no significant change for light fragments, but increases with the mass for intermediate and heavy products. The dynamical effect on isoscaling is reflected on the α decreasing a little with the evolution time of the system, and opposite trend for the heavy products. The secondary decay effect on isoscaling is reflected on the increasing of the α value for the final products which experienced secondary decay process. Furthermore the density dependence of the symmetry energy has also been explored for the primary and secondary products, the symmetry energy coefficient can be expressed by the form of Csym(ρ) ~ C0(ρ/ρ0)γ, C0 and γ extracted from the primary products are consistent with the input parameters, but C0 and γ extracted from the final products deviate the input values. In the paper we also suggest that it might be more reasonable to describe the density dependence of the symmetry energy coefficient by the Csym(ρ/ρ0) ≈ C1(ρ/ρ0)γsoft + C2(ρ/ρ0)γstiff with γsoft ≤ 1, γstiff ≥ 1 and C1, C2 constant parameters.

THE ORIENTATIONAL-AVERAGE EFFECTS OF HEAVY-ION COLLISIONS INDUCED BY DEFORMED NUCLEI AT INTERMEDIATE ENERGY

The deformed projectiles and targets are expected to play different roles in heavy-ion collisions (HICs) at intermediate energy compared with spherical ones. With an isospin dependent quantum molecular dynamics (IDQMD) model, in despite of averaging all the orientations of axisymmetric deformed 24Mg + 24Mg collisions, it is still found that NN collision number, nuclear stopping power (R) and multiplicity of fragments have considerable differences compared with spherical 24Mg + 24Mg collisions.

PROJECTILE FRAGMENTATION OF (36,40)Ar INDUCED REACTIONS

Fragment yields of projectile fragmentation reactions using primary beams of 36,40Ar at 50 MeV/nucleon on 64Ni target have been measured. Fragment yields of different isotopes were obtained for Z ≥ 5 in RIBLL fragment seperator. We compare the extracted yields to the predictions of the empirical parametrization of fragmentation cross-sections(EPAX) and Statistical Abration-Ablation model(SAA) considering the RIBLL separator transmission rate. Isotope yield ratios between these 2 reactions were calculated, isoscaling parameters α and β, their dependence on fragment atomic number Z and neutron number N were calculated.

PROJECTILE FRAGMENTATION OF36,40Ar INDUCED REACTIONS

Fragment yields for Z ≥ 5 from projectile fragmentation using primary beams of 36,40Ar at 50 MeV/nucleon on 64Ni target have been measured in RIBLL fragment separator. We compare the fragment cross sections with the predictions of the empirical EPAX parametrization of fragmentation cross-sections and Statistical Abration-Ablation model (SAA) by considering the RIBLL separator transmission rate. Isotope yield ratios between these two reactions were calculated and isoscaling parameters α and β are extracted, their dependences on fragment atomic number Z and neutron number N were presented.

Measurements of reaction cross section and fragment momentum distribution for N=10 proton-rich isotones

The longitudinal momentum (p//) distributions of fragments after one-proton removal and reaction cross sections (σR) for several N = 10 isotones at intermediate energy (~ 70A MeV) have been measured simultaneously at the RIken Projectile fragment Separator (RIPS). p// was measured using a direct time-of-flight (TOF) technique, while σR was determined using a transmission method. An enhanced σR is observed for 23Al comparing with its neighbors. The p// distribution for 22Mg fragments from 23Al one-proton removal reaction has been obtained for the first time. The experimental data are discussed within a Few Body Glauber (FBG) framework. Analysis of p// indicates a dominant d-wave component in the ground state of 23Al. This agrees with recent experimental results. We also suggest the possibility of an enlarged 22Mg core for proton-rich nucleus 23Al.