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[en] The density dependence of the symmetry energy in the equation of state of isospin asymmetric nuclear matter is studied using the isoscaling of the fragment yields and the antisymmetrized molecular dynamic calculation. It is observed that the experimental data at low densities are consistent with the form of symmetry energy, E_sym≅31.6(ρ/ρ_circle)^0.69, in close agreement with those predicted by the results of variational many-body calculation. A comparison of the present result with those reported recently using the NSCL-MSU data suggests that the heavy ion studies favor a dependence of the form, E_sym≅31.6(ρ/ρ_circle)^γ, where γ=0.6-1.05. This constrains the form of the density dependence of the symmetry energy at higher densities, ruling out an extremely 'stiff' and 'soft' dependences

[en] The symmetry energy is an important quantity in the equation of state of isospin asymmetric nuclear matter. This currently unknown quantity is key to understanding the structure of systems as diverse as the neutron-rich nuclei and neutron stars. At TAMU, we have carried out studies, aimed at understanding the symmetry energy, in a variety of reactions such as, the multifragmentation of 40Ar, 40Ca + 58Fe, 58Ni and 58Ni, 58Fe + 58Ni, 58Fe reactions at 25 - 53 AMeV, and deep-inelastic reactions of 86Kr + 124,112Sn, 64,58Ni (25 AMeV), 64Ni + 64,58Ni, 112,124Sn, 232Th, 208Pb (25 AMeV) and 136Xe + 64,58Ni, 112,124Sn, 232Th, 197Au (20 AMeV). Here we present an overview of some of the results obtained from these studies. The results are analyzed within the framework of statistical and dynamical models, and have important implications for future experiments using beams of neutron-rich nuclei

[en] The density dependence of the symmetry energy in the equation of state of isospin asymmetric nuclear matter is of significant importance for studying the structure of systems as diverse as the neutron-rich nuclei and the neutron stars. A number of reactions using the dynamical and the statistical models of multifragmentation, and the experimental isoscaling observable, are studied to extract information on the density dependence of the symmetry energy. It is observed that the dynamical and the statistical model calculations give consistent results assuming the sequential decay effect in dynamical model to be small. A comparison with several other independent studies is also made to obtain important constraints on the form of the density dependence of the symmetry energy. The comparison rules out an extremely 'stiff' and 'soft' forms of the density dependence of the symmetry energy with important implications for astrophysical and nuclear physics studies

[en] We have investigated the disassembly of light nuclear systems with charge 12-15 to extract the power-law parameters of the fragmenting nuclear system. Excited nuclei were produced in semiperipheral reactions ²⁸Si+^112,124Sn at 30 and 50 MeV/nucleon and the residual cold fragments were detected by the multidetector array for charged particles FAUST. We have studied the power-law parameter τ as a function of the excitation energy of quasiprojectiles. We observe a systematic occurrence of the minimum of τ with respect to the excitation energy accompanied by the maximum of the second moment of the charge distribution in the same region of excitation energy. The main features observed in the characteristics of mass and charge distributions for multifragmentation of heavier systems, such as power-law behavior of charge distribution, are thus observed also for very light systems. Moreover, behavior of the charge distribution with respect to the N/Z degree of freedom has been shown

[en] Current advances in technology have enabled dramatic improvements to the performance of multi-detector arrays within the last 10 years. FAUST is a forward array of 68 Si-CsI(Tl) detector telescopes that has been in use since 1996. To take full advantage of current technology, FAUST has undergone an overhaul installing new preamplifiers from Zepto Systems and modifications to allow for Dual-Axis Dual-Lateral position sensitive detectors to be installed. A new calibration software package has also been developed utilizing a novel linearization algorithm. The combination of these upgrades has led to isotopic identification for elements in the Z = 1-13 range and has greatly increased the angular resolution of the array.

[en] The evolution of the symmetry energy coefficient of the binding energy of hot fragments with increasing excitation is explored in multifragmentation processes following heavy-ion collisions below the Fermi energy. In this work, high-resolution mass spectrometric data on isotopic distributions of projectile-like fragments are systematically compared to calculations involving the statistical multifragmentation model (SMM). Within the SMM picture, the present study suggests a gradual decrease of the symmetry energy coefficient of the hot primary fragments from 25 MeV at the compound nucleus regime towards 15 MeV in the multifragmentation regime. The isotopic distributions of the hot primary fragments are found to be very wide and extend towards the neutron drip line. These findings are expected to have important implications in the modeling of the composition and the evolution of hot and dense astrophysical environments, such as those of core-collapse supernova

[en] Nuclear fragment yield data has been analyzed using the Landau free energy description to investigate the critical phenomena in the fragmentation of quasiprojectile in the reactions ^78,86Kr+^58,64Ni at beam energy of 35 MeV/nucleon. The data on mirror nuclei yield ratio for A=3 and 7 showed an exponential dependence on the isospin asymmetry of the quasiprojectile as predicted by the Landau free energy approach. The slope parameter, obtained from linear fit to the plots of the logarithm of mirror nuclei yield ratios as a function of isospin asymmetry of the fragmenting source provided a reasonable estimate of the nuclear symmetry energy, and showed a systematic decrease with increasing excitation energy of the quasiprojectile.

[en] Assuming a schematic form of the nucleon effective mass as a function of nuclear excitation energy and mass, we provide a simple explanation for understanding the experimentally observed mass dependence of the nuclear caloric curve. It is observed that the excitation energy at which the caloric curve enters into a plateau region could be sensitive to the nuclear mass evolution of the effective nucleon mass

[en] In this work, the isoscaling for the ⁴⁰Ca+^112,124Sn reactions at the beam energy of 45 MeV/A was investigated as a function of the excitation energy of reconstructed quasi-projectiles. The excitation energy dependence of the isoscaling parameter obtained from the intra-system isoscaling was investigated and is expected to provide information for the determination of the symmetry energy coefficient of highly excited nuclei.