The Symmetry Energy from the Neutron-Rich Nucleus Produced in the Intermediate-Energy ^40,48Ca and ^58,64Ni Projectile Fragmentation

In the framework of a modified Fisher model, using the isobaric yield ratio method, we investigate the fragments produced in the 140 A MeV ^40,48Ca+⁹Be and ^58,64Ni+⁹Be projectile fragmentation reactions. Using different approximation methods, a_sym/T (the ratio of symmetry?energy coefficient to temperature) of symmetric and neutron-rich fragments are extracted. It is found that a_sym/T of fragments depend on the reference nucleus and the neutron excess of fragments. The a_sym/T of the isobar decreases when the neutron?excess of the isobar increases, while for a fragment with the same neutron-excess, a_sym/T increases as the mass of the fragment increases but saturate when the mass of the fragment becomes larger.