The Isospin Effect In Heavy Ion Collisions At Intemediate Energy And The Studies On The Equation Of State

The current studies on heavy-ion collisions at intermediate energy are of broad scientific interest. One of the main motivation for these studies is to extract information of the Equation of State (EoS) of nuclear matter, especially the density dependence of the symmetry energy term. The symmetry energy term in the EoS are very important for understanding many intersting astrophysical phenomena. But it is also a subject with large uncertainties, especially its density dependence form of the symmetry energy. Therefor, to acquire more accurate knowledge of the symmetry energy term in the EoS becomes one of the main goals in nuclear physics at present, and has driven a lot of theoretical and experimental efforts.We have developed a new version of Improved Quantum Molecular Dynamical model (ImQMD) for studing these problems. The main improvments are as follows: l).In order to study the dynamical effects of the density dependence of the symmetry potential on heavy-ion collisions by means of transport theory, we verify the symmetry energy with the nolinear form of the density dependence of the bulk symmetry potential energy in the potential energy density functional. 2). In collision term, isospin dependent nucleon-nulceon scattering cross sections and the isospin dependent Pauli blocking effect are used in our model. 3). we introduced a self-consistent isoscalar and isovector potential based on the Skyrme energy density functional in our microscopic transport model, and the momentum dependence interaction is also take into accout. 4). new treament of the Pauli blocking in collision part are adopted, and a phenomenological density dependent in-medium nucleon-nucleon cross sections are used.Based on new version of ImQMD model, the peripherial heavy-ion collisions of ^112,124Sn +⁸⁶ Kr at Eb=25AMeV are studied in order to seek those obsevables that are sensitive to the symmetry potential. For peripheral heavy-ion collisions, that nucleons, light charged particles, and very few intermediate mass fragments are emitted mainly in the compressed neck region. The density of PLF^*/TLF^* is always around the normal density and it means that thereis no compression happening for PLF"/TLF*. Our study shows that the N/Z ratio of emitted nucleons, isotope distributions of light charged particles calculated with soft symmetry potential are more neutron rich than that with stiff symmetry, and the heavy residue isotope distributions show an opposite trends, i.e., the stiff symmetry potential produce more neutron rich isotope than the soft symmetry potential for the conservation of the N/Z ratio of the reaction system. Our results show that the slope of the average N/Z ratio of emitted nucleons vs impact parameters for these reactions is sensitive to the density dependence of the symmetry energy. The N/Z ratio increase with impact parameters and the increase slope with stiff symmetry potential is about twice as large as those with soft symmetry potential. The ratio of Y(3H)/Y(3He) in central collisions are also depend on the symmetry potential stiffness, the ratio of Y(3H)/Y(sHe) calculated with soft symmetry potential are larger than that with stiff symmetry potential. The difference between the calculated results calculated with stiff and soft symmetry potential is enhanced for neutron rich reaction systems. We also analysis the isoscaling law of the light charged particles and heavy residues. Our results show that the Isoscaling parameters a values of the light charged particles and heavy residues depend on the symmetry potential. The a values of light charged particles and heavy residues calculated with soft symmetry potential are larger than that with the stiff symmetry potential.We have further studied the dynamical effect of the different Equation of State on heavy ion collisions with our new version of the ImQMD model. We find that charge distributions of products in heavy ion collisions calculated with Skyrme force -Skp parameters (corresponding the soft EoS) are in good agreement with the experiments at incident energies ranging from the Fermi energy to 400AMeV. We pay main attention on studing the influence of different: EoS on the collective flow in HICs. For the stiffcr equation of state can generate larger pressure than the softer EoS, so. the directed and elliptical flow calculated with the stiff EoS are stronger than that with the soft EoS at higher incident energy above the transition energy EiTans. The excitation functions ofelliptical flow alsoshow an isospin effect that neutron rich reaction systems can generate more negative values of v-i- We systematically studied the elliptical flow excitation function for several reaction systems, and the results show the system size dependence of the directed flow and elliptical flow. The influence of the momentum dependent interaction and the in-medium nucleon-nucleon cross section o*nn are also checked, and we find they are very important for correctly describing the excitation function of elliptical flow. We have also studied the influence of different EoS on the yield of light charge particles, the yield of 3H and 3/7e are also depend on the stiffness of the Equation of State. The yield of 3H and 3He calculated with the stiffer equation of state (SIII) are obviously lower than that with the softer EoS(Skp, Skm*, Sly7).