Isospin nonequilibrium in heavy-ion collisions at intermediate energies

Li, Bao-An; Yennello, S. J.

doi:10.1103/physrevc.52.r1746

Cited by 57 publications

(62 citation statements)

References 9 publications

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“…While it is important to develop practically implementable quantum transport theories, applications of the semi-classical transport models have enabled us to learn a great deal of interesting physics from heavy-ion reactions, especially the EOS of symmetric nuclear matter. With the development of radioactive ion beam physics, several rather comprehensive isospin-dependent, but mostly semi-classical transport models [23,25,26,29,30,50,56,57], have been successfully developed in recent years to describe nuclear reactions induced by neutron-rich nuclei at intermediate and high energies.…”

Section: Introductionmentioning

confidence: 99%

Recent progress and new challenges in isospin physics with heavy-ion reactions

2008

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The ultimate goal of studying isospin physics via heavy-ion reactions with neutron-rich, stable and/or radioactive nuclei is to explore the isospin dependence of in-medium nuclear effective interactions and the equation of state of neutron-rich nuclear matter, particularly the isospin-dependent term in the equation of state, i.e., the density dependence of the symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of the nuclear symmetry energy has been the main focus of the intermediate-energy heavy-ion physics community during the last decade, and significant progress has been achieved both experimentally and theoretically. In particular, a number of phenomena or observables have been identified as sensitive probes to the density dependence of the nuclear symmetry energy. Experimental studies have confirmed some of these interesting isospin-dependent effects and allowed us to constrain relatively stringently the symmetry energy at sub-saturation densities. The impacts of this constrained density dependence of the symmetry energy on the properties of neutron stars have also been studied, and they were found to be very useful for the astrophysical community. With new opportunities provided by the various radioactive beam facilities being constructed around the world, the study of isospin physics is expected to remain one of the forefront research areas in nuclear physics. In this report, we review the major progress achieved during the last decade in isospin physics with heavy ion reactions and discuss future challenges to the most important issues in this field.Key words: Equation of state of asymmetric nuclear matter, Nuclear symmetry energy, Heavy-ion reactions with neutron-rich nuclei, Neutron skin thickness of heavy nuclei, Neutron stars Constraining the Skyrme effective interactions and the neutron skin thickness of heavy nuclei using terrestrial nuclear laboratory data 216 8

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Section: Introductionmentioning

confidence: 99%

Recent progress and new challenges in isospin physics with heavy-ion reactions

2008

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“…A fast redistribution of neutrons and protons takes place between the interacting projectile and target during the interaction time and is responsible for the process of N/Z (or isospin) equilibration. At medium energies, relevant work [30][31][32][33][34][35] indicated that essentially above the Fermi energy isospin equilibrium is not reached even for the most damped collisions. In these studies, isotopic or isobaric yield ratios of selected light or intermediatemass fragments were used to probe isospin equilibration in semi-peripheral to near-central collisions.…”

Section: Introductionmentioning

confidence: 99%

“…More sophisticated microscopic approaches have also been adopted including semiclassical mean-field transport models of Boltzmann-type such as BUU (BoltzmannUehling-Ulenbeck) [9,31,48,49], BNV (BoltzmannNordheim-Vlasov) [11,50], SMF (Stochastic Mean Field) [11,51] and the fully quantal TDHF (time-dependent Hartree-Fock) approach [52][53][54]. Furthermore, N-body approaches of Quantum Molecular Dynamics (QMD) type [55] have been applied such as the Constrained Molecular Dynamics (CoMD) model [56,57] employed in this work.…”

Section: Introductionmentioning

confidence: 99%

Isoscaling of heavy projectile residues andN/Zequilibration in peripheral heavy-ion collisions below the Fermi energy

et al. 2014

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The isoscaling of heavy projectile residues from peripheral heavy-ion reactions at 15-25 MeV/nucleon is employed to obtain information on the process of N/Z equilibration. Recent mass spectrometric data of projectile residues from the reactions of 86 Kr (15 MeV/nucleon) with 64,58 Ni and 124,112 Sn were first analyzed. The isotopically resolved yield distributions of the fragments in the range Z=26-39 were employed for the isoscaling analysis. The yield ratios R21(N,Z) of the fragments from each pair of systems exhibit isoscaling (i.e. an exponential dependence on the fragment neutron number N for each atomic number Z) with the isoscaling parameter α increasing with decreasing (or increasing) Z away from the projectile. This variation is related to the evolution toward N/Z equilibration with increasing energy dissipation estimated from the residue velocities. In parallel to the new heavy-residue isoscaling data of 86 Kr at 15 MeV/nucleon, our previous data at 25 MeV/nucleon for the reactions 86 Kr+ 124,112 Sn and 64 Ni+ 64,58 Ni, 64 Ni+ 124,112 Sn, as well as our data at 15 MeV/nucleon of the lighter system 40 Ar+ 64,58 Ni were analyzed in a similar way. Calculations with the stochastic nucleon-exchange model DIT (Deep Inelastic Transfer) and the microscopic many-body model CoMD (Constrained Molecular Dynamics) provided an overall fair description of data and valuable guidance for their interpretation. Interestingly, the data of the 86 Kr+Ni,Sn reactions at 15 MeV/nucleon show a retardation of the process of N/Z equilibration which, as suggested by the CoMD calculations, is indicative of the collective character of the process. This retardation is not present in the investigated systems at 25 MeV/nucleon (and the light 40 Ar+Ni systems at 15 MeV/nucleon), whose behavior is found to be consistent with stochastic nucleon exchange.

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“…1. Moreover, in contrast to the case at 30 MeV/A, the reaction time at 400 MeV/A is much too short compared to the time necessary for the system to reach the global isospin equilibrium [32,33]. A good quantitative measure of the isospin transport is the neutron to proton ratio at mid-rapidity.…”

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Observable effects of symmetry energy in heavy-ion collisions at intermediate energies

2004

Phys. Rev. C

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Within an isospin-dependent transport model for nuclear reactions induced by neutron-rich nuclei, we perform a comparative study of 100 Sn + 124 Sn and 100 Zn+ 124 Sn reactions at beam energies of 30 MeV/A and 400 MeV/A to identify optimal experimental conditions and observables for investigating the equation of state (EOS) of neutron-rich matter at RIA. Several observables known to be sensitive to the density-dependence of the symmetry energy are examined as a function of impact parameter for both reaction systems. In particular, the strength of isospin transport/diffusion is studied by using rapidity distributions of free nucleons and their isospin asymmetries. An approximate isospin equilibrium is established even for peripheral collisions with a very soft symmetry energy at 30 MeV/A. At 400 MeV/A, however, a strong isospin translucency is observed even in most central collisions with either soft or stiff symmetry energies. Origins of these observations and their implications to determining the EOS of neutron-rich matter at the Rare Isotope Accelerator (RIA) are discussed.

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Isospin nonequilibrium in heavy-ion collisions at intermediate energies

Cited by 57 publications

References 9 publications

Recent progress and new challenges in isospin physics with heavy-ion reactions

Recent progress and new challenges in isospin physics with heavy-ion reactions

Isoscaling of heavy projectile residues andN/Zequilibration in peripheral heavy-ion collisions below the Fermi energy

Observable effects of symmetry energy in heavy-ion collisions at intermediate energies

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