Pre-equilibrium γ-ray emission induced in the 40Ca+48Ca system at 10 MeV/nucleon and isospin equilibration processes

In the present paper we have studied γ-ray emission in coincidence with charged particles measured in binary processes for the collisions Ca40+Ca48, Ti46 at 10 MeV/nucleon. The comparison between γ-ray yields, obtained under identical conditions on the charged particles detected in coincidence, shows an extra yield of around 15 MeV for the Ca40+Ca48 collision. The analysis of the γ-charged fragment coincidence events, along with the study performed with the dynamical model CoMD-II, explains this effect as the result of a giant dipole resonance emission from the intermediate system, characterized by a high degree of coherence. The performed study aims to establish a link among pre-equilibrium γ-ray emission, initial charge/mass ratio memory effects in the intermediate system for the Ca40+Ca48 system at short time, and the achievement of a substantial charge/mass ratio or isospin equilibration of the primary fragments formed at longer time. Moreover, the presence of a remarkable extra yield in a restricted range of the γ-ray spectra suggests that this equilibration process evolves through a quasiresonant mechanism. © 2005 The American Physical Society.