Isoscaling of mass A≃40 reconstructed quasiprojectiles from collisions in the Fermi energy regime

Isoscaling studies of fragments with Z=1-8 from reconstructed quasiprojectiles of mass A≃40 from the Ar40+Sn124, 112Sn and Ca40+Sn124, 112Sn reactions at beam energy of 45 MeV/nucleon were performed. After initial efforts to obtain isoscaling with the “traditional” approach of using pairs of systems differing in their isospin asymmetry (or neutron-to-proton ratio N/Z), “intra-system” isoscaling for each of these four systems was obtained using fragment sources restricted in two narrow N/Z regions (one neutron-rich and one neutron-poor). The observed isoscaling behavior was excellent and the isoscaling parameter α was found to decrease with increasing excitation energy. Corrections due to undetected neutrons were also taken into account in the source N/Z determination by using the theoretical models DIT (Deep Inelastic Transfer) and SMM (Statistical Multifragmentation Model) along with a software replica of the experimental setup. These corrections were applied to the determination of the parameter Δ (expressing the difference in the isospin asymmetry of the two sources used in the isoscaling). The reduced isoscaling parameter α/Δ was obtained and found to decrease as the excitation energy of the quasiprojectile source increases, in good agreement with recent work on reconstructed mass A≃80 quasiprojectiles. This decrease of α/Δ may point to a decrease of the symmetry energy coefficient with increasing excitation energy.