Dynamical dipole mode in heavy-ion fusion reactions

C Parascandolo,E De Filippo,A Del Zoppo,C Mazzocchi,A Guglielmetti,M Trimarchi,U Emanuele,F Farinon,G Inglima,C Signorini,C Agodi,R Coniglione,M Mazzocco,R Alba,M La Commara,B Martin,C Maiolino,D Pierroutsakou,A Boiano,M Sandoli,M Romoli ,A Trifirò ,Riccardo Silvestri ,D Santonocito

doi:10.1016/j.nuclphysa.2009.12.039

Abstract

The dynamical dipole mode, excited in charge asymmetric heavy-ion collisions, was investigated in the mass region of the 192Pb compound nucleus, formed by using the 40,48Ca + 152,144Sm reactions at ∼11 MeV/nucleon. Preliminary results of this measurement, concerning both fusion-evaporation and fission events are presented. As a fast cooling mechanism on the fusion path, the dynamical dipole mode could be useful for the synthesis of super heavy elements through “hot” fusion reactions.

Highlights

The “Dynamical Dipole mode" (DD throughout the text), or pre-equilibrium Giant Dipole Resonance, is a collective oscillation of protons against neutrons with a dipole spatial pattern inside the atomic nucleus
The DD radiation is characterized by the following characteristics: i) a centroid energy lower than that of the compound nucleus GDR in the same mass region indicating a high deformation of the emitting source [3, 4] ii) an anisotropic angular distribution with respect to the beam axis since the oscillation is confined in the reaction plane [6] and iii) a γ yield that should depend on both the reaction dynamics and the symmetry term of the nuclear matter Equation Of State [4]
These events are characterized by emission of pre-equilibrium light particles that reduces the compound nucleus average mass, average charge and average excitation energy and cannot be discarded in the time of flight (TOF) spectrum of the reaction products because they have overlapping velocity distributions with those of the complete fusion events [23]

Summary

Introduction

The “Dynamical Dipole mode" (DD throughout the text), or pre-equilibrium Giant Dipole Resonance, is a collective oscillation of protons against neutrons with a dipole spatial pattern inside the atomic nucleus It is a pre-equilibrium phenomenon, being excited along the fusion path of nuclei with a different ratio of neutrons and protons and decaying through emission of prompt γ-rays [1,2,3,4,5]. On the other hand few experimental results exist reporting on the DD γ multiplicity and on its angular distribution, that can be directly compared with calculations These elements called for more experimental efforts to disentagle the influence of each reaction parameter on the DD features and to provide severe constraints to the theoretical models. In order to understand the behavior of the DD in heavier systems than those studied before and to test its usefulness in super-heavy element production, we decided to study the DD in a composite system in the mass region A=190 [17]

The experiment

Analysis and Results

Fusion–evaporation results

Fission: preliminary results

Conclusion