Entrance channel effects in medium mass nuclear systems at 25 MeV/nucleon

I Lombardo ,F Amorini ,G Lanzalone ,G Verde ,G Giuliani ,A Pagano ,E De Filippo ,C Agodi ,Jifeng Han ,M Trimarchi ,E Rosato ,L Acosta ,E Geraci ,I Berceanu ,C Maiolino ,E La Guidara ,G Cardella ,L Grassi ,F Rizzo ,G Politi ,P Russotto ,D Loria ,T Minniti ,A Anzalone ,L Auditore ,M B Chatterjee ,A Trifirò ,M Papa ,S Pirrone ,F Porto ,M Vigilante

doi:10.1088/1742-6596/515/1/012013

Abstract

We discuss experimental data concerning 48Ca+48Ca and 42Ca+54Fe reactions at 25 MeV/nucleon obtained by using the 4π multi-detector Chimera. Effects due due to the different neutron to proton ratios (N/Z) of the two systems have been investigated. Charge distributions of forwardly emitted fragments show even-odd staggering whose amplitude is larger for the neutron poor system. Moreover, the neutron excess of the total system influence the evolution of fusion-like sources formed in semi-central collisions. In particular, for the neutron rich system, the relative emission yield of heavy residues is larger, while multi-fragmentation and binary-like events prevail in the neutron poor system.

Highlights

The possibility of performing nuclear reactions between heavy ions with different charge and neuron number allows to investigate effects related to the different entrance channels [1]
Charge distributions of light fragments emitted at forward angles show evenodd staggering effects with a large amplitude in the case of the more neutron poor system, while for the neutron rich system the relative probability of heavy residue emission is favored
Combining the results of the present analysis and of Refs. [6, 26] it seems that the relative yield of events leading to the formation of an heavy residue is larger for the more neutron rich systems, and the present effect can be mainly attributed to the N/Z degree of freedom and not to the mass asymmetry or the total mass of entrance channels

Summary

Introduction

The possibility of performing nuclear reactions between heavy ions with different charge and neuron number allows to investigate effects related to the different entrance channels [1]. Data concerning systems with noticeable differences in N/Z have been increasingly reported in the literature [3, 4] In this way, it was possible to investigate in details the effects played by the isospin degree of freedom on various aspects of reaction dynamics, such as the co-existence of various competitive mechanisms [5, 6], the neutron exchange between reaction partners (isospin diffusion) [7, 8, 9, 10] and the neutron enrichment of low-density regions formed in peripheral collisions (isospin drift) [5, 10, 11]. Charge distributions of light fragments emitted at forward angles show evenodd staggering effects with a large amplitude in the case of the more neutron poor system, while for the neutron rich system the relative probability of heavy residue emission is favored The results of these analysis will be briefly discussed . For the neutron poor system (42Ca+54Fe) a quite large emission of carbon isotopes is seen, while the yields of boron and fluorine isotopes relatively to beryllium are quite similar for the two systems

Semi-central events of reactions: heavy residue emission

Findings

Conclusions