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.. MeV Ca-40,Ca-48+Be-9 and Ni-58,Ni-64+Be-9 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.