Progress of quantum molecular dynamics model and its applications in heavy ion collisions

In this review article,we first briefty introduce the transport theory and quantum molecular dynamics model applied in the study of the heavy ion collisions from low to intermediate energies.The developments of improved quantum molecular dynamics model(ImQMD)and ultra-relativistic quantum molecular dynamics model(UrQMD),are reviewed.The reaction mechanism and phenomena related to the fusion,multinucleon transrer,fragmentation,collective flow and particle production are reviewed and discussed within the framework of the two models.The constraints on the isospin asymmetric muclear equation of state and in-medium nucleon nucleon cross sections by comparing the heavy ion collision data with transport models calculations in last decades are also discussed,and the uncertainties of these constraints are analyzed as well.Finally,we discuss the future direction of the development of the transport models for improving the understanding of the reaction mechanism,the descriptions of various observables,the constraint on the nuclear equation of state,as well as for the constraint on in-medium nucleon-nucleon cross sections.

Influence of the neck parameter on the fission dynamics within the two-center shell model parametrization

The influence of the neck parameter on the fission dynamics at low excitation energy is studied based on the three-dimensional Langevin approach,in which the nuclear shape is described with the two-center shell model(TCSM)parametrization,and the elongation,mass asymmetry,and fragment deformation are set to be the generalized coordinates of the Langevin equation.We first study the influence of the neck parameter on the scission configuration.We find that there is almost no obvious correlation between the neck parameter and mass asymmetryηat the scission point,indicating that has no evident impact on the fragment mass distribution.The elongation Z_(0)=R_(0) and its correlation with the mass asymmetryηat the scission point are clearly influenced by the neck parameter,which has a strong effect on the total kinetic energy(TKE)distribution of the fragments.The pre-neutron emission fragment mass distributions for 14 MeV n+^(233;235;238)U and^(239)Pu are calculated,and then,based on these results,the post-neutron emission fragment mass distributions are obtained by using the experimental data of prompt neutron emission.The calculated post-neutron emission fragment mass distributions can reproduce the experimental data well.The TKE distributions for 14 MeV n+^(235)U fission are calculated for ε=0.25,0.35,and 0.45,and the results show that the TKE distribution cannot be described very well for the three cases.However,the trend of the calculated TKE distribution withεis just as expected from the scission configuration calculations.The results with ε=0.35 present a better agreement with the experiment data compared with the other two cases.