Abstract
Fusion cross sections have been measured in the 40 Ca + 58 Ni and 40 Ca + 64 Ni systems at energies around and below the Coulomb barrier. The 40 Ca beam was delivered by the XTU Tandem accelerator of the Laboratori Nazionali di Legnaro and evaporation residues were measured at very forward angles with the LNL electrostatic beam deflector. Coupled-channels calculations were performed which highlight possible strong effects of neutron transfers on the fusion below the barrier in the 40 Ca + 64 Ni system. Microscopic time-dependent Hartree-Fock calculations have also been performed for both systems. Preliminary results are shown.
Highlights
The fusion process accounts for the major part of the reaction cross section in collisions of heavy ions at above the barrier beam energies
In the symmetric 40Ca + 40Ca and 48Ca + 48Ca systems, all nucleon transfer channels have negative Q values. To put it in a nutshell, strong couplings to octupole vibrational states are observed in the fusion of the Ca+Ca systems at Coulomb barrier (CB) and below, fusion hindrance is measured at very deep sub-barrier energies in the asymmetric 40Ca + 48Ca collision as well as effects of neutron transfer channels
The same type of calculation including couplings to the relevant states, was performed for 40Ca + 64Ni. This is shown by the red solid line of Fig. 1. This underestimates the cross sections at sub-barrier energies and it was found that good reproduction of the data is obtained if a 2n transfer channel is included in the CC calculations in some schematical way
Summary
The fusion process accounts for the major part of the reaction cross section in collisions of heavy ions at above the barrier beam energies. In the 40,48Ca+40,48Ca cases, a fusion hindrance was reported at deep sub-barrier energies for 40Ca + 48Ca. The effect is different for 40Ca + 40Ca and 40Ca + 48Ca, because of the coupling to the strong 3− state in the soft 40Ca nucleus with regard to the 48Ca stiff nucleus. Besides including all couplings to low-lying excited states of the target and projectile in the CC calculations, it has been shown that it is necessary to take into account transfer channel effects to best describe the 40Ca + 48Ca data.
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