N/Z effects on nuclear reactions near the multi-fragmentation threshold
Dipartimento di Scienze Fisiche, Università Federico II, Napoli, Italy
2 INFN - Sezione di Napoli, Via Cinthia, 80126, Napoli, Italy
Revised: 25 July 2012
Accepted: 27 July 2012
Published online: 27 August 2012
We investigate effects that can be attributed to the neutron-to-proton ratio (N/Z) degree of freedom by studying nuclear reactions 40, 48Ca + 40, 48Ca and 40Ca + 46Ti at 25 MeV/nucleon. We used the Chimera 4π detector as detection device. Even-odd staggering in Z and N distributions of light fragments have been seen. They can be attributed, in a qualitative way, to the de-excitation phase of pre-fragments. By selecting central events of reaction, where fusion-like sources can be formed, we observe that the emission of heavy residues is more favored in the case of neutron rich entrance channels; this effect could be attributed to the interplay between Coulomb and symmetry terms in the nuclear equation of state, as obtained by comparing experimental data with CoMD-II model calculations. We characterized also thermodynamically hot-fusion-like sources formed in central collisions; in this case, the studied systems show similar apparent temperatures. In semi-peripheral collisions, isospin diffusion effects have been found. From the data analysis it seems that, at this bombarding energy, the neutron-to-proton ratio degree of freedom does not have time to distribute uniformly in the interacting di-nuclear system.
© Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg, 2012