Symmetry energy and the isoscaling properties of the fragments produced in ⁴⁰Ar, ⁴⁰Ca+⁵⁸Fe, ⁵⁸Ni reactions at 25, 33, 45, and 53 MeV/nucleon

The symmetry energy and the isoscaling properties of the fragments produced in the multifragmentation of ⁴⁰Ar, ⁴⁰Ca+⁵⁸Fe, ⁵⁸Ni reactions at 25, 33, 45, and 53 MeV/nucleon were investigated within the framework of statistical multifragmentation model. The isoscaling parameters α, from the primary (hot) and secondary (cold) fragment yield distributions, were studied as a function of excitation energy, isospin (neutron-to-proton asymmetry), and fragment symmetry energy. It is observed that the isoscaling parameter α decreases with increasing excitation energy and decreasing symmetry energy. The parameter α 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, when studied as a function of excitation energy and isospin of the fragmenting system, show very little influence on the isoscaling parameter. The symmetry energy, however, has a strong influence on the isospin properties of the hot fragments. The experimentally observed scaling parameters can be explained by symmetry energy that is significantly lower than that for the ground-state nuclei near saturation density. The results indicate that the properties of hot nuclei at excitation energies, densities, and isospin away from the normal ground-state nuclei could be significantly different.