Strong enhancement of dynamical emission of heavy fragments in the neutron-rich 124Sn+64Ni reaction at 35A MeV

A quantitative comparison is made between the absolute cross sections associated with statistical and dynamical emission of heavy fragments in the 124Sn+64Ni and 112Sn+58Ni collisions experimentally investigated at 35A MeV beam energy using the multidetector CHIMERA. The result shows that the dynamical process is about twice as probable in the neutron-rich 124Sn+64Ni system as in the 112Sn+58Ni neutron-poor one. This unexpected and significant difference indicates that the reaction mechanism is strongly dependent on the entrance-channel isospin (N/Z) content

Time sequence and time scale of intermediate mass fragments emission

Semiperipheral collisions in the 124Sn+64Ni reaction at 35MeV/nucleon were studied using the forward part of the Charged Heavy IonMass and Energy ResolvingArray. Nearly completely determined ternary events involving projectilelike fragments (PLF), targetlike fragments (TLF), and intermediatemass fragments (IMF) were selected. A new method of studying the reaction mechanism, focusing on the analysis of the correlations between relative velocities in the IMF+PLF and IMF+TLF subsystems, is proposed. The relative velocity correlations provide information on the time sequence and time scale of the neck fragmentation processes leading to production of IMFs. It is shown that the majority of light IMFs are produced within 40–80 fm/c after the system starts to reseparate. Heavy IMFs are formed at times of about 120 fm/c or later and can be viewed as resulting from two-step (sequential) neck rupture processes