Eur. Phys. J. Plus (2012) 127: 88
https://doi.org/10.1140/epjp/i2012-12088-8

Regular Article

N/Z effects on nuclear reactions near the multi-fragmentation threshold

¹ Dipartimento di Scienze Fisiche, Università Federico II, Napoli, Italy
² INFN - Sezione di Napoli, Via Cinthia, 80126, Napoli, Italy

^* e-mail: ivlombardo@na.infn.it
^** e-mail: ilombardo@lns.infn.it

Received: 24 May 2012
Revised: 25 July 2012
Accepted: 27 July 2012
Published online: 27 August 2012

Abstract

We investigate effects that can be attributed to the neutron-to-proton ratio (N/Z) degree of freedom by studying nuclear reactions ^{40, 48}Ca + ^{40, 48}Ca 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.