Dependent Quantum Molecular Dynamics Model Research Articles

Azimuthal-sensitive three-dimensional HBT radius in Au–Au collisions at $$E_{beam} = 1.23A$$ GeV by the IQMD model

We used an Isospin dependent Quantum Molecular Dynamics (IQMD) model to simulate Au + Au collisions at beam energy $$E_{beam}$$ = 1.23A GeV, which corresponds to center of mass energy $$\sqrt{s_{NN}} = 2.4$$ GeV. Firstly, we obtained reasonable rapidity and transverse mass spectra of $$\pi ^-$$ and $$\pi ^+$$ as well as “apparent” temperature parameters in comparison with the HADES data. Then by calculating three-dimensional Hanbury Brown and Twiss (HBT) radius of same charged pion-pairs, we obtained the square difference of outward radius and sideward radius, i.e. $$R_{out}^{2}-R_{side}^{2}$$ , as well as the freeze-out volume ( $$V_{fo}$$ ), which were basically consistent with the trend of HADES experimental results. The azimuthal dependence of the HBT radii was also calculated by a matrix method, and corrected by the rotation matrix. In addition, the eccentricities of the xy- and zy- planes of pion-pair emissions were also extracted for different pair transverse momentum and collision centrality, which show that the xy-eccentricity increases with pair transverse momentum as well as centrality but not for zy-eccentricity, indicating a more asymmetric transverse emission of particle-pairs with higher transverse momentum in off-central collisions.

Prediction of the cross-sections of isotopes produced in deuteron-induced spallation of long-lived fission products * * Supported by the National Natural Science Foundation of China (11875328)

The spallation cross-section data for the long-lived fission products (LLFPs) are scarce but required for the design of accelerator driven systems. In this paper, the isospin dependent quantum molecular dynamics model and the statistical code GEMINI are applied to simulate deuteron-induced spallation in the energy region of GeV/nucleon. By comparing the calculations with the experimental data, the applicability of the model is verified. The model is then applied to simulate the spallation of 90Sr, 93Zr, 107Pd, and 137Cs induced by deuterons at 200, 500 and 1000 MeV/nucleon. The cross-sections of isotopes, the cross-sections of long-lived nuclei, and the reaction energy are presented. Using the above observables, the feasibility of LLFP transmutation by spallation is discussed.

Memory loss in central heavy-ion collisions at intermediate energy

Using isospin dependent quantum molecular dynamics model (IQMD) a comprehensive interpretation regarding the memory loss in nuclear stopping has been conducted. It is observed that with the increase in energy more nucleons lose their memory and participate in nuclear stopping. We have performed the systematic study of the mass dependence of memory loss and its linear correlation with the allowed collisions. Our study serves as a baseline for the understanding of the memory loss in nuclear stopping.

Heavy-ion collision dynamics: Correlation with elliptic flow and nuclear stopping

A comprehensive interpretation regarding the collision dynamics in heavy-ion collisions, using isospin dependent quantum molecular dynamics model (IQMD) has been conducted. Our study serves as a baseline for the collision dynamics and its correlation with elliptic flow and nuclear stopping. In the physical interpretation of nucleus–nucleus collisions, ‘centrality’ of the collisions, play significant role. Elliptic flow and nuclear stopping shows strong correlation with the number of nucleons participating in collision dynamics.

Investigation of nuclear stopping observable in heavy ion collisions

Detailed analysis has been made on nuclear stopping using various observable. Transport model, isospin dependent quantum molecular dynamics model (IQMD) has been used to study stopping over the whole mass range at incident energies between 10 MeV/nucleon and 1000 MeV/nucleon. Our study proves that ratio of width of transverse to longitudinal rapidity distribution i.e., <varxz> is the most suitable parameter to study nuclear stopping. Also, it has been observed that light mass fragments (LMF's) emitted from participant region can be used as barometer to study nuclear stopping.

Influence of isospin dependent nuclear charge radii on fragmentation in heavy ion collisions

Abstract We study the initialization effects via nuclear charge radii on fragmentation for the whole mass range of periodic table by taking isospin asymmetric nuclear reactions using Isospin dependent Quantum Molecular Dynamics (IQMD) model. Calculations are performed for three different isospin dependent nuclear charge radii parameterizations as well as for liquid drop model (LDM) radius. Our study reveals that there is a significant role of nuclear charge radii on fragmentation in heavy ion collisions at intermediate energies. The influence on fragmentation due to initialization via nuclear charge radii is more for heavier colliding nuclei compared to lighter colliding nuclei and this influence further reduces with increase in incident energy for lighter colliding nuclei and remains nearly constant for heavier colliding nuclei. Moreover, isospin dependent radius is more suitable to reproduce experimental findings of INDRA Collaboration.

Analyzing the role of isospin content and colliding geometry on the transition energy for symmetric colliding nuclei

We explore the effect of isospin content (N/Z) and colliding geometry on the transition energy throughout the mass range between 72 and 394 for isotopes, isobars and isotones. The analysis has been performed within the framework of the isospin dependent quantum molecular dynamics model for symmetric colliding nuclei. Our findings indicate that the impact parameter dependence of transition energy follows a power law behavior. Moreover, the percentage change in the transition energy with and without symmetry energy (or with an isospin independent nucleon–nucleon cross-section) is higher for the lighter colliding nuclei. Further, the N/Z dependence of the transition energy for lighter nuclei can act as a good probe to constrain the density dependence of symmetry energy at a supra-saturation density. Our findings are in good agreement with the experimental measurements of the Identification de Noyaux et Detection avec Resolutions Accrues, Michigan State University and Gesellschaft für Schwerionenforschung collaborations.

Role of model ingredients on the directed flow and its disappearance using isospin dependent quantum molecular dynamics model

We study the effect of different equations of state, momentum dependence of nuclear forces and in-medium nucleon-nucleon cross-sections on the directed flow and its disappearance. Our findings reveal that soft momentum-dependent equation of state along with reduced cross-section shows good agreement with the experimentally observed mass dependence of balance energy.

Sensitivity of the transition energy towards mass asymmetry of the colliding nuclei

We investigate the role of the mass asymmetry on the transition energy by studying asymmetric reactions using the isospin dependent quantum molecular dynamics (IQMD) model. Substantial and the uniform e ect of the asymmetry of the reaction has been observed on the transition energy. Moreover, isospin e ects shows a small influence on the mass asymmetry ( ) dependence of transition energy.

Effect of momentum dependent interactions and nucleonic cross-section on directed flow [formula omitted

The descriptive analysis for the effect of momentum dependent interactions and nucleonic cross-section (isospin dependent and isospin-independent) on the neutron–proton directed flow (v1), within the framework of the isospin dependent quantum molecular dynamics model is presented. Our study shows that, the directed flow of both neutrons and protons is affected by the momentum dependence of nuclear equation of state and the isospin dependence of nucleon–nucleon cross-section. A soft momentum dependent (SM) equation of state is found to be more compatible with the experimental data.

PHASE SPACE ANALYSIS ON ORIGIN OF ANISOTROPIC FLOW

Using the isospin dependent quantum molecular dynamics model, we study the phase space distribution of the nucleons coming from participant matter that are contributing in flow. The distribution of nucleons and fragments is not symmetric around the beam axis. Our study shows that the nucleon which suffer maximum number of collisions are contributing in anisotropic flow.

Effect of isospin-dependent cross-section on fragment production in the collision of charge asymmetric nuclei

To understand the role of isospin effects on fragmentation due to the collisions of charge asymmetric nuclei, we have performed a complete systematical study using isospin dependent quantum molecular dynamics model. Here simulations have been carried out for $^{124}X_{n}+ ^{124}X_{n}$, where n varies from 47 to 59 and for $^{40}Y_{m}+ ^{40}Y_{m}$, where m varies from 14 to 23. Our study shows that isospin dependent cross-section shows its influence on fragmentation in the collision of neutron rich nuclei.

Anisotropic distribution of nucleon participating in elliptical flow

Using the isospin dependent quantum molecular dynamics model, we study the effect of charge asymmetry and isospin dependent cross-section on dNd(〈cos2ϕ〉) and dNptdpt. Simulations have been carried out for the reactions of Xm124+Xm124, where m=(47,50 and 59) and S1640+S1640. Our study shows that these parameters depend strongly on the isospin of cross-section and charge asymmetry. The distribution of free nucleons is symmetric but the distribution of nucleons constituting the light mass fragments, which are contributing in elliptical flow, is not symmetric around the beam axis.

Influence of charge asymmetry and isospin-dependent cross section on nuclear stopping

Using the isospin dependent quantum molecular dynamics model, we study the effect of charge asymmetry and isospin dependent cross-section on nuclear stopping and multiplicity of free nucleons and LMF's. Simulations were carried out for the reactions $^{124}X_{m}+^{124}X_{m}$, where m varies from 47 to 59 and for $^{40}Y_{n}+^{40}Y_{n}$, where n varies from 14 to 23. Our study shows that nuclear stopping as well as the production of LMF's depend strongly on the isospin of the cross-section.

Isospin and symmetry energy study in nuclear EOS

This paper summarizes the isoscaling and isospin related studies in asymmetry nuclear reactions by different dynamic and statistical 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 difference Delta mu(n) or Delta mu(p) as a function of temperature, or in free neutron and proton chemical potential difference Delta mu(n)-Delta mu(p). Density dependence of symmetry energy coefficient C-sym(rho/rho(0)) 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 simulation 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 symmetry energy of the nuclear equation of state (EOS). GDR can also be regarded as a possible isospin sensitive signature.

Multifragmentation around the transition energy in intermediate-energy heavy-ion collisions

Fragmentation of light charged particles is studied for various systems at different incident energies between 50 and 1000 MeV/nucleon. We analyze fragment production at incident energies above, below and at transition energies using the isospin dependent quantum molecular dynamics(IQMD) model. The trends observed for the fragment production and rapidity distributions depend upon the incident energy, size of the fragments, composite mass of the reacting system as well as on the impact parameter of the reaction. The free nucleons and light charged particles show continous homogeneous changes irrespective of the transition energies indicating that there is no relation between the transition energy and production of the free as well as light charged particles.

Dynamics of strangeness production in heavy-ion collisions near threshold energies

Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the dynamics of strangeness (K$^{0,+}$, $\Lambda$ and $\Sigma^{-,0,+}$) production in heavy-ion collisions near threshold energies is investigated systematically, in which the strange particles are considered to be mainly produced by the inelastic collisions of baryon-baryon and pion-baryon. The collisions in the region of supra-saturation densities of the dense baryonic matter formed in heavy-ion collisions dominate the yields of strangeness production. The total multiplicities as functions of incident energies and collision centralities are calculated with the Skyrme parameter SLy6. The excitation function of strangeness production is analyzed and also compared with the KaoS data for the K$^{+}$ production in the reactions $^{12}$C+$^{12}$C and $^{197}$Au+$^{197}$Au.

Effects of the entrance channel mass asymmetry in fusion reactions

The symmetric and asymmetric fusion reaction systems forming the same compound nuclei 26Al, 30Si, 38Ar and 170Hf are investigated with the frame of improved isospin dependent quantum molecular dynamics model. The entrance channel mass asymmetry dependence of compound nucleus formation is found by analyzing the shell correction energies, the Coulomb barriers and the fusion cross sections. The calculated fusion cross sections agree quantitatively with the experimental data. The results indicate that compound nucleus formation is favorable for the systems with larger mass asymmetry because of the smaller Coulomb contribution to the fusion barrier.

PROBING THE SYMMETRY ENERGY AT SUPRA-SATURATION DENSITIES FROM PION EMISSION IN HEAVY-ION COLLISIONS

Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the emission of pion in heavy-ion collisions in the region 1 A GeV as a probe of nuclear symmetry energy at supra-saturation densities is investigated systematically, in which the pion is considered to be mainly produced by the decay of resonances Δ(1232) and N *(1440). The π-/π+ yields are calculated for selected Skyrme parameters SkP, SLy6, Ska and SIII, and also for the cases of different stiffness of symmetry energy with the parameter SLy6. Preliminary results compared with the measured data by the FOPI collaboration favor a hard symmetry energy of the potential term proportional to (ρ/ρ0)γs with γs = 2.

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 24 Mg + 24 Mg collisions, it is still found that NN collision number, nuclear stopping power (R) and multiplicity of fragments have considerable differences compared with spherical 24 Mg + 24 Mg collisions.