Symmetry energy and the isoscaling properties of the fragments in multifragmentation of 40Ca+58Ni, 40Ar+58Ni, and 40Ar+58Fe reactions

The symmetry energy and the isoscaling properties of the fragments produced in multifragmentation of 40Ar, 40Ca + 58Fe, 58Ni reactions at 25, 33, 45 and 53 MeV/nucleon were investigated within the framework of a statistical multifragmentation model. The isoscaling parameter, ???? from the hot primary and cold secondary fragment yield distributions, was studied as a function of the excitation energy, isospin (neutronto- proton asymmetry), and fragment symmetry energy. Through changing the symmetry energy in the statistical multifragmentation model to describe the experimental data, it is observed that the isoscaling parameter ???? decreases with increasing excitation energy and decreases with decreasing symmetry energy. The parameter ???? is also observed to increase with increasing difference in the isospin of the fragmenting system. The sequential decay of the primary fragments into secondary fragments show very little influence on the isoscaling parameter when studied as a function of excitation energy. However, the symmetry energy has a strong influence on the isospin properties of the hot fragments. The results indicate that the isospin properties of the fragments produced at high excitation energy and reduced density in multifragmentation reactions are sensitive to the symmetry energy, indicating that the properties of hot nuclei at excitation energies, densities, and isospin away from normal ground state nuclei are significantly different than those of normal (cold) nuclei at saturation density.