Quantum molecular dynamics simulation formultifragmentation resulting from an expandingnuclear matter

Quantum molecular dynamics (QMD) is used to investigate multifragmentation resulting from an expanding nuclear matter. Equation of state, the structure of nuclear matter and symmetric nu-clear matter is discussed. Also, the dependence of the fragment mass distribution on the initial temperature (Tinit) and the radial flow velocity (h) is studied. When h is large, the distribution shows exponential shape, whereas for small h, it obeys the exponentially falling distribution with mass number. The cluster formation in an expanding system is found to be different from the one in a thermally equilibrated system. The used Hamiltonian has a classical kinetic energy term and an effective potential term composed of four parts.

Hot Nuclei Multifragmentation and Cascade Partition Method

The conditional moment correlation and distribution are calculated by a self-similarity cascadepartition method.The results calculated are in agreernent with the experimental data of 3.7 and 14.6GeV/u 28Si fragmentation in nuclear emulsion.

Collision Dynamics and Multifragmentation Process in Heavy Ion Collisions

-By using the improved quantum molecular dynamics(IQMD),we have stu-died the influences of items such as the nucleon-nucleon(N-N)collision cross sectionwith or without the medium effect,the momentum dependent interactions(MDI),theequation of state(EOS)and the aggregating method for fragments on the multifrag-mentation process of heavy ion collisions with different beam energies.It is found thatmultifragmentation distribution patterns,the collective flows of fragments and singleparticles,the collision number,and the nuclear matter density all depend strongly on theN-N cross section,the momentum dependent interactions and the nuclear equation ofstate;especially,these dependences are associated with beam energies.However,thefragment multiplicity distribution patterns depend very weakly on the equation of state.

From Sequential Processes to Multifragmentation in Proton Reactions with Gold

The distribution of relative angles between the intermediate mass fragments has been measured and analyzed for thermal multifragmentation in p + Au collisions at 2.1, 3.6 and 8.1 GeV. The analysis has been done on an event by event basis. The multibody Coulomb trajectory calculations of all charged particles have been performed starting with the initial break-up conditions given by the combined model with the revised intranuclear cascade (INC) followed by the statistical multifragmentation model. The measured correlation function was compared with the calculated one to find the actual time scale of the intermediate mass fragment (IMF) emission. It found transition from sequential evaporation for p(2.1 GeV) + Au to simultaneous multibody decay of a hot and expanded nuclear system in case of p(8.1 GeV) + Au.

SCALING PROPERTIES OF NUCLEAR MULTIFRAGMENTATION

Under given conditions, for instance, by heavy-ion collisions at intermediate and high energies, nuclei can break into several pieces. This new reaction mechanism is called nuclear multifragmentation. In analogy with a macroscopic system where a critical phenomenon takes place, nuclear multifragmentation also shows .the scaling properties. However, these properties can only be described partly by the restructured aggregation

Isospin dependence of nuclear multifragmentation in statistical model

The evolution of nuclear disintegration mechanisms with increasing excitation energy, from compound nucleus to multifragmentation, has been studied by using the Statistical Multifragmentation Model （SMM） within a micro-canonical ensemble. We discuss the observable characteristics as functions of excitation energy in multifragmentation, concentrating on the isospin dependence of the model in its decaying mechanism and break-up fragment configuration by comparing the A0 = 200, Z0 = 78 and A0 = 200, Z0 = 100 systems. The calculations indicate that the neutron-rich system （Z0 = 78） translates to a fission-like process from evaporation later than the symmetric nucleus at a lower excitation energy, but gets a larger average multiplicity as the excitation energy increases above 1.0 MeV/u.

The Time Evolution of Radial Collective Flow in Reaction of ^(197)Au with ^(197)Au at 150 MeV/u

Dynamical time evolution for central collision of 197 Au on 197Au at 150 MeV/u is in-vestigated by using Isospin-dependent Quantum Molecular Dynamics （IQMD） calculation. Thepreequilibrium emission, its influence and the time evolution of radial collective flow are dis-cussed in detail.

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.

Multiplicities of forward-backward particles in ^(16)O-emulsion interactions at 4.5 AGeV/c

An exclusive study of the characteristics of interactions accompanied by backward emission（θlab 90°） of shower and grey particles in collisions of a 4.5 AGeV/c ^16O beam with emulsion nuclei is carried out. The experimental multiplicity distributions of different particles emitted in the forward（θlab 〈 90°） and backward hemispheres due to the interactions with the two emulsion components（CNO,AgBr） are presented and analyzed. The correlations between the different emitted particles are also investigated. The results indicate that there are signatures for a collective mechanism,which plays a role in the production of particles in the backward hemisphere. Hence,the backward multiplicity distribution of the emitted shower and grey particles at 4.5 AGeV/c incident momentum can be represented by a decay exponential law formula independent of the projectile size. The exponent of the power was found to increase with decreasing target size. The experimental data favor the idea that the backward particles were emitted due to the decay of the system in the latter stages of the reactions.