Abstract
Early data of sub-barrier fusion teached us that cross sections may strongly depend on the structure of colliding nuclei and on couplings to transfer channels. The influence of transfer is clearly indicated in the excitation functions of different nickel isotopes and various Ca+Zr systems. Fusion barrier distributions often yield the fingerprint of the relevant inelastic and transfer couplings. At lower energies, far below the barrier the slope of the excitation function keeps increasing in many cases, so that the cross sections are strongly over-predicted by standard coupled-channels (CC) calculations; this was named a hindrance effect.Furthermore, light heavy-ion systems show cross section oscillations above the Coulomb barrier. Recent experiments have been performed on the fusion of 28,30 Si+ 28,30 Si systems where all phenomena cited above show up. In particular regular oscillations that have been revealed above the barrier for 28 Si+ 28 Si and have been interpreted as the consequence of the strong channel couplings and/or the oblate deformation of 28 Si.
Highlights
Data of sub-barrier fusion teached us that cross sections may strongly depend on the structure of colliding nuclei and on couplings to transfer channels
The fusion excitation functions have been plotted in a appropriate reduced energy scale to take into account the different Coulomb barriers and the high energy octupole vibrations of 40Ca and 48Ca [5, 6]
In the energy region far below the Coulomb barrier fusion cross sections result from a balance between the enhancement produced by couplings which are dominant at energies close to the barrier, and the more recently observed hindrance phenomenon [8]
Summary
Data of sub-barrier fusion teached us that cross sections may strongly depend on the structure of colliding nuclei and on couplings to transfer channels. The effect of coupling to transfer channels was revealed in several cases, and one of the most significant evidences was observed in the trend of the Ca + Zr systems which show very different behaviours as reported in Fig. 2 (left panel).
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