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. Als...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.展开更多
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 <sup>28<...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 <sup>28</sup>Si fragmentation in nuclear emulsion.展开更多
-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 interact...-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.展开更多
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 ...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.展开更多
The experimental data concerning the58Ni+48Ca reaction at Elab(Ni)=25A MeV,collected by using the CHIMERA 4π device,have been analyzed in order to investigate the competition among different reaction mechanisms for c...The experimental data concerning the58Ni+48Ca reaction at Elab(Ni)=25A MeV,collected by using the CHIMERA 4π device,have been analyzed in order to investigate the competition among different reaction mechanisms for central collisions in the Fermi energy domain.As a main criterion for centrality selection we have chosen the flow angle(flow) method,making an event-by-event analysis that considers the shape of events,as it is determined by the eigenvectors of the experimental kinetic-energy tensor.For the selected central events(flow >60°) some global variables,good to characterize the pattern of central collisions have been constructed.The main features of the reaction products were explored by using different constraints on some of the relevant observables,like mass and velocity distributions and their correlations.Much emphasis was devoted,for central collisions,to the competition between fusion-evaporation processes with subsequent identification of a heavy residue and a possible multifragmentation mechanism of a well defined(if any) transient nuclear system.Dynamical evolution of the system and pre-equilibrium emission were taken into account by simulating the reactions in the framework of transport theories.Different approaches have been envisaged(dynamical stochastic BNV calculations + sequential SIMON code,QMD,CoMD,etc.).Preliminary comparison of the experimental data with BNV calculations shows reasonable agreement with the assumption of sequential multifragmentation emission in the mass region of IMFs close to the heavy residues.Possible deviations from sequential processes were found for those IMFs in the region of masses intermediate between the mass of heavy residues and the mass of light IMFs.Further simulations are in progress.The experimental analysis will be enriched also by information obtained inspecting the IMF-IMF correlation function,in order to elucidated the nature of space-time decay property of the emitting source associated with events having the largest IMF multiplicity.展开更多
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 ...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展开更多
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 mi...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.展开更多
Dynamical time evolution for central collision of <sup>197</sup> Au on <sup>197</sup>Au at 150 MeV/u is in-vestigated by using Isospin-dependent Quantum Molecular Dynamics （IQMD） calculation....Dynamical time evolution for central collision of <sup>197</sup> Au on <sup>197</sup>Au 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.展开更多
The heavy-ion phase-space exploration (HIPSE) model is used to discuss the origin of the nuclear spin in intermediate energy heavy-ion collision (HIC).The spin of maximal projectile-like fragment is found to depend st...The heavy-ion phase-space exploration (HIPSE) model is used to discuss the origin of the nuclear spin in intermediate energy heavy-ion collision (HIC).The spin of maximal projectile-like fragment is found to depend strongly on impact parameter of a reaction system,while it relates weakly to the collision violence.Some interesting multi-fragmentation phenomena related to the spin are shown.We also found that the excitation energy in the de-excitation stage plays a robust role at the de-excitation stage in HIC.展开更多
New theoretical calculations are performed to investigate the Coulomb proximity and angular momentum effects on multifragmentation picture for84Kr+112,124 Sn collisions at an incident beam energy of 35 Me V/nucleon.Ch...New theoretical calculations are performed to investigate the Coulomb proximity and angular momentum effects on multifragmentation picture for84Kr+112,124 Sn collisions at an incident beam energy of 35 Me V/nucleon.Charge and isotopic distributions and the mean neutron-to-proton ratios of the fragments are reproduced within the microcanonical Markov chain calculations on the basis of Statistical Multifragmentation Model. It is shown that the Coulomb interactions and angular momentum effects are very important to reproduce isotopic composition of nuclear fragments in peripheral heavy-ion collisions at Fermi energies. Our results imply that it is possible to investigate in laboratories the modification of structure parameters of fragments, such as the symmetry energy coefficient, at subnuclear densities in dense environment of other species.展开更多
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 improv...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.展开更多
文摘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.
文摘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 <sup>28</sup>Si fragmentation in nuclear emulsion.
基金The project supported by National Natural Science Foundation of ChinaScience Foundation of Academia Sinica.
文摘-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.
文摘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.
文摘The experimental data concerning the58Ni+48Ca reaction at Elab(Ni)=25A MeV,collected by using the CHIMERA 4π device,have been analyzed in order to investigate the competition among different reaction mechanisms for central collisions in the Fermi energy domain.As a main criterion for centrality selection we have chosen the flow angle(flow) method,making an event-by-event analysis that considers the shape of events,as it is determined by the eigenvectors of the experimental kinetic-energy tensor.For the selected central events(flow >60°) some global variables,good to characterize the pattern of central collisions have been constructed.The main features of the reaction products were explored by using different constraints on some of the relevant observables,like mass and velocity distributions and their correlations.Much emphasis was devoted,for central collisions,to the competition between fusion-evaporation processes with subsequent identification of a heavy residue and a possible multifragmentation mechanism of a well defined(if any) transient nuclear system.Dynamical evolution of the system and pre-equilibrium emission were taken into account by simulating the reactions in the framework of transport theories.Different approaches have been envisaged(dynamical stochastic BNV calculations + sequential SIMON code,QMD,CoMD,etc.).Preliminary comparison of the experimental data with BNV calculations shows reasonable agreement with the assumption of sequential multifragmentation emission in the mass region of IMFs close to the heavy residues.Possible deviations from sequential processes were found for those IMFs in the region of masses intermediate between the mass of heavy residues and the mass of light IMFs.Further simulations are in progress.The experimental analysis will be enriched also by information obtained inspecting the IMF-IMF correlation function,in order to elucidated the nature of space-time decay property of the emitting source associated with events having the largest IMF multiplicity.
文摘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
基金Supported by Natural Science Foundation of China (10975064, 10905041, 11005171)General Programs of Social Science Research Fund of Ministry of Education of China (10YJAZH137)
文摘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.
文摘Dynamical time evolution for central collision of <sup>197</sup> Au on <sup>197</sup>Au 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.
基金Partially supported by NSFC of China under contract No.11035009,No.10979074,No.10875160,No.10805067 and No.10975174the 973-Program under contract No.2007CB815004+1 种基金the Shanghai Development Foundation for Science and Technology under contract No.09JC1416800the Knowledge Innovation Project of CAS under Grant No.KJCX2-EW-N01
文摘The heavy-ion phase-space exploration (HIPSE) model is used to discuss the origin of the nuclear spin in intermediate energy heavy-ion collision (HIC).The spin of maximal projectile-like fragment is found to depend strongly on impact parameter of a reaction system,while it relates weakly to the collision violence.Some interesting multi-fragmentation phenomena related to the spin are shown.We also found that the excitation energy in the de-excitation stage plays a robust role at the de-excitation stage in HIC.
基金Supported by Turkish Scientific and Technical Research Council(No.113F058)Scientific Research Coordination of Selcuk University(BAP)(No.SU-2014/14701490)Helmholtz International Center for FAIR(LOEWE program)
文摘New theoretical calculations are performed to investigate the Coulomb proximity and angular momentum effects on multifragmentation picture for84Kr+112,124 Sn collisions at an incident beam energy of 35 Me V/nucleon.Charge and isotopic distributions and the mean neutron-to-proton ratios of the fragments are reproduced within the microcanonical Markov chain calculations on the basis of Statistical Multifragmentation Model. It is shown that the Coulomb interactions and angular momentum effects are very important to reproduce isotopic composition of nuclear fragments in peripheral heavy-ion collisions at Fermi energies. Our results imply that it is possible to investigate in laboratories the modification of structure parameters of fragments, such as the symmetry energy coefficient, at subnuclear densities in dense environment of other species.
基金Yingxun Zhang acknowledges the supports in part by the National Natural Science Foundation of China(Grant Nos.11875323,11875125,11475262,10675172,11075215,11475262,11790323,11790324,11790325,and 11961141003)the National Key R&D Program of China(Grant No.2018YFA0404404)+15 种基金the Continuous Basic Scientific Research Project(No.WDJC-2019-13)Ning Wang acknowledges the supports in part by the National Natural Science Foundation of China(Nos.U1867212 and 11422548)the Guangxi Natural Science Foundation(Nos.2015G XNSFDA139004,2017G XNSFG A198001)Qingfeng Li acknowledges the supports in part by the National Natural Science Foundation of China(Nos.11875125,11847315,11375062,11505057,11947410,and 11747312)the Zhejiang Provincial Natural Science Foundation of China(No.LY18A050002)the“Ten-Thousand Talent Program”of Zhejiang ProvinceJunlong Tian acknowledges the supports in part by the National Science Foundation of China(Nos.11961131010 and 11475004)Li Ou acknowledges the supports in part by the National Natural Science Foundation of China(No.11965004)the Natural Science Foundation of Guangxi Province(No.2016GXNSFFA380001)Foundation of Guangxi Innovative Team and Distinguished Scholar in Institutions of Higher EducationMin Liu acknowledges the supports in part by the National Natural Science Foundation of China(No.11875323)Kai Zhao acknowledges the supports in part by the National Natural Science Foundation of China(Nos.11675266,11005155,11475262,11275052,11375062,11547312,and 11275068)the National Key Basic Research Developm ent Program of China(Nos.2007CB209900 and 2013CB834404)Xizhen Wu acknowledges the supports in part by the National Natural Science Foundation of China(Nos.10235020,10979023,11005155,11365004,11475004,and 11675266)Zhuxia Li acknowledges the supports in part by the National Natural Science Foundation of China(Nos.19975073,10175093,10175089,10235030,11275052,11375062,11475262,11475004,11875323,and 11875125)the National Key Basic Research Development Program of China(Nos.G20000774 and 2007CB209900).
文摘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.
