Isoscaling of mass A similar or equal to 40 reconstructed quasiprojectiles from collisions in the Fermi energy regime

摘要

Isoscaling studies of fragments with Z = 1-8 from reconstructed quasiprojectiles of mass A similar or equal to 40 from the Ar-40 + Sn-124. Sn-112 and Ca-40 + Sn-124. Sn-112 reactions at beam energy of 45 MeVucleon 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 behaviour was excellent and the isoscaling parameter alpha 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 Delta (expressing the difference in the isospin asymmetry of the two sources used in the isoscaling). The reduced isoscaling parameter alpha/Delta 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 similar or equal to 80 quasiprojectiles. This decrease of alpha/Delta may point to a decrease of the symmetry energy coefficient with increasing excitation energy.