QM（苏前敏） Su

Isospin influences on particle emission and critical phenomena in nuclear dissociation

Features of particle emission and critical point behavior are investigated as functions of the isospin of disassembling sources and temperature at a moderate freeze-out density far medium-size Xe isotopes in the framework of the isospin-dependent lattice gas model. Multiplicities of emitted light particles, isotopic, and isobaric ratios of light particles show the strong dependence on the isospin of the dissociation source, but double ratios of light isotope pairs and the critical temperature determined by the extreme values of some critical observables are insensitive to the isospin of the systems. Values of the power law parameter of cluster mass distribution, mean multiplicity of intermediate mass fragments (IMF), information entropy, and Campis second moment also show a minor dependence on the isospin of Xe isotopes at the critical point. In addition, the slopes of the average multiplicities of the neutrons (N-n), protons (N-p), charged particles (N-CP), and IMFs (N-IMF), slopes of the largest fragment mass number (A(max)), and the excitation energy per nucleon of the disassembling source (E*/A) to temperature are investigated as well as variances of the distributions of N-n, N-p, N-CP, N-IMF, A(max), and E*/A. It is found that they can be taken as additional judgements to the critical phenomena. [S0556-2813(99)302108-1].

Excitation energy as a basic variable to control nuclear disassembly

Abstract: Thermodynamical features of Xe system is investigated as functions of temperature and freeze-out density in the frame of lattice gas model. The calculation shows different temperature dependence of physical observables at different freeze-out density. In this case, the critical temperature when the phase transition takes place depends on the freeze-out density. However, a unique critical excitation energy %and the same excitation reveals regardless of freeze-out density when the excitation energy is used as a variable instead of temperature. Moreover, the different behavior of other physical observables with temperature due to different ρf vanishes when excitation energy replaces temperature. It indicates that the excitation energy can be seen as a more basic quantity to control nuclear disassembly.

PROJECTILE FRAGMENTATION OF (36,40)Ar INDUCED REACTIONS

Fragment yields of projectile fragmentation reactions using primary beams of 36,40Ar at 50 MeV/nucleon on 64Ni target have been measured. Fragment yields of different isotopes were obtained for Z ≥ 5 in RIBLL fragment seperator. We compare the extracted yields to the predictions of the empirical parametrization of fragmentation cross-sections(EPAX) and Statistical Abration-Ablation model(SAA) considering the RIBLL separator transmission rate. Isotope yield ratios between these 2 reactions were calculated, isoscaling parameters α and β, their dependence on fragment atomic number Z and neutron number N were calculated.

STUDY OF ISOSCALING PHENOMENA FOR PROJECTILE-LIKE FRAGMENTS

In the framework of a modified statistical abrasion-ablation (SAA) model, the isospin effect and isoscaling behavior in projectile fragmentation have been systematically investigated. The normalized peak differences and reduced isoscaling parameters are found to decrease with (Zproj-Z)/Zproj and have no significant dependence on the size of reaction systems. The linear dependence of α and |β| on or for projectile-like fragments is demonstrated, which is obtained for light fragments from multifragmentation in the grand-canonical limit. Assuming a Fermi-gas behavior, the excitation energy dependence of the symmetry energy coefficients are tentatively extracted from α and β which looks consistent with the experimental data. It is pointed out that the reduced isoscaling parameters can be used as an observable to study the excitation extent of system and asymmetric nuclear equation of state in heavy ion collisions.