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[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 multifragmentation of quasiprojectiles was studied in the reactions of a ²⁸Si beam with ¹¹²Sn and ¹²⁴Sn targets at projectile energies of 30 and 50 MeV/nucleon. The quasiprojectile observables were reconstructed using isotopically identified charged particles with Z_f≤5 detected at forward angles. The nucleon exchange between projectile and target was investigated using the isospin and the excitation energy of the reconstructed quasiprojectile. For events with total reconstructed charge equal to the charge of the beam (Z_tot=14), the influence of the beam energy and target isospin on the neutron transfer was studied in detail. Simulations were carried out employing a model of deep inelastic transfer, a statistical model of multifragmentation, and a software replica of the FAUST detector array. The concept of deep inelastic transfer provides a good description of the production of highly excited quasiprojectiles. The isospin and excitation energy of the quasiprojectile were described with good overall agreement. The fragment multiplicity, charge and isospin were reproduced satisfactorily. The range of contributing impact parameters was determined using a backtracing procedure

[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] We have created quasiprojectiles of varying isospin via peripheral reactions of ²⁸Si+¹¹²Sn and ¹²⁴Sn at 30 and 50 MeV/nucleon. The quasiprojectiles have been reconstructed from completely isotopically identified fragments. The difference in N/Z of the reconstructed quasiprojectiles allows the investigation of the disassembly as a function of the isospin of the fragmenting system. The isobaric yield ratio ³H/³He depends strongly on N/Z ratio of quasiprojectiles. The dependences of mean fragment multiplicity and mean N/Z ratio of the fragments on N/Z ratio of the quasiprojectile are different for light charged particles and intermediate mass fragments. Observation of a different N/Z ratio of light charged particles and intermediate mass fragments is consistent with an inhomogeneous distribution of isospin in the fragmenting system

[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] Interest in the influence of the neutron-to-proton (N/Z) ratio on multifragmenting nuclei has demanded an improvement in the capabilities of multi-detector arrays as well as the companion analysis methods. The particle identification method used in the NIMROD-ISiS 4π array is described. Performance of the detectors and the analysis method are presented for the reaction of ⁸⁶Kr+⁶⁴Ni at 35 MeV/u.

[en] The enhancement in the production of even-Z nuclei observed in nuclear fission has also been observed in fragments produced from heavy ion collisions. Beams of ⁴⁰Ar, ⁴⁰Cl, and ⁴⁰Ca at 25 MeV/nucleon were impinged on ⁵⁸Fe and ⁵⁸Ni targets. The resulting fragments were detected using the MSU 4π detector array, which had additional silicon detectors for better isotopic resolution. Comparison of the ratios of yields for each element showed enhancement of even-Z fragment production. The enhancement was more pronounced for reactions with a greater difference in the N/Z of the compound system. However, this effect was less for systems that were more neutron rich. The average N/Z for fragments also displayed an odd-even effect with a lower average N/Z for the even-Z fragments. This is related to the greater availability of neutron-poor isotopes for even-Z nuclei

[en] Heating of nuclear matter with 8 GeV/c bar p and π^- beams has been investigated in an experiment conducted at BNL AGS accelerator. All charged particles from protons to Z ≅ 16 were detected using the Indiana Silicon Sphere 4π array. Significant enhancement of energy deposition in high multiplicity events is observed for antiprotons compared to other hadron beams. The experimental trends are qualitatively consistent with predictions from an intranuclear cascade code

[en] Multifragmentation studies induced by GeV light-ion beams permit investigation of the influence of intrinsic thermal properties of hot nuclear matter, with minimal interference from the compression/decompression cycle and rotational instabilities. We summarize recent results obtained with ³He, proton and pion beams up to 15 GeV/c and present the initial results from a recent experiment with 8 GeV/c antiproton and pion beams. The results are compared with INC simulations coupled to EES and SMM models and the caloric curve for the ³He data will also be discussed