Fusion Hindrance and Quadrupole Collectivity in Collisions of A≃50 Nuclei: The Case of48Ti +58Fe

A M Stefanini,N Toniolo,F Haas,C Parascandolo,S Courtin,G Montagnoli,L Corradi,D Torresi,D Bourgin,F Scarlassara,E Fioretto,M Mazzocco,J Grebosz,T Mijatović,D Montanari,E Strano,S Szilner,A Goasduff

doi:10.1051/epjconf/20158600057

Abstract

The fusion excitation function of 48 Ti + 58 Fe has been measured in a wide energy range around the Coulomb barrier, covering 6 orders of magnitude of the cross sections. We present here the preliminary re- sults of this experiment, and a full comparison with the near-by system 58 Ni + 54 Fe where evidence of fusion hindrance shows up at relatively high cross sections. The sub-barrier cross sections of 48 Ti + 58 Fe are much larger than those of 58 Ni + 54 Fe. Significant differences are also observed in the logarithmic derivatives, astro- physical S-factors and fusion barrier distributions. The influence of low-energy nuclear structure on all these trends is pointed out and commented. Coupled-channels calculations using a Woods-Saxon potential are able to reproduce the experimental results for 48 Ti + 58 Fe. The logarithmic derivative of the excitation function is very nicely fit, and no evidence of hindrance is observed down to around 1 μb. The fusion barrier distribution is rather wide, flat and structureless. It is only in qualitative agreement with the calculated distribution.

Highlights

In the collision of two heavy ions at energies near and below the Coulomb barrier, couplings of the relative motion of the two nuclei to their low-energy surface vibrations and/or stable deformations [1, 2] determine the cross sections
The lower energy limit of such distributions, it has been shown in recent years [6, 7] that fusion excitation functions show a sharp decrease with decreasing energy, well below the expectations based on standard coupled-channels (CC) calculations
The fusion excitation function has been presented, and a significant irregularity of its logarithmic slope has been observed below the Coulomb barrier, but no evidence of hindrance shows up in the measured energy range

Summary

Introduction

In the collision of two heavy ions at energies near and below the Coulomb barrier, couplings of the relative motion of the two nuclei to their low-energy surface vibrations and/or stable deformations [1, 2] determine the cross sections. Multi-phonon excitations have been shown [3] to become dominant for medium-heavy nuclei and produce complex fusion barrier distributions, possibly with discrete structures [4, 5]. The lower energy limit of such distributions, it has been shown in recent years [6, 7] that fusion excitation functions show a sharp decrease with decreasing energy, well below the expectations based on standard coupled-channels (CC) calculations.

Results

Conclusion