Seminaire "Fusion hindrance in light- and heavy-systems" Giovanna Montagnoli

jeudi 20 sept. 2018, 10:45 → 12:00 Europe/Paris

Mondrian

The phenomenon of hindrance in sub-barrier heavy-ion fusion will be introduced and several experimental evidences show that it is a general phenomenon. It is recognized in many cases by the trend of the logarithmic slope of excitation function  and of the S factor at low energies. The comparison with standard Coupled-Channels calculations is a more quantitative evidence for its existence.

Hindrance is observed in light systems, independent of the sign of the fusion Q-value, with different features. In the case of the 12C+ 30Si system the hindrance effect is small but it is clearly recognized.  Near-by cases show evidence for systematic behaviors. The consequences for the dynamics of stellar evolution have to be clarified  by further experimental and theoretical work.

Possible  interpretations of hindrance will be shortly illustrated, including a recent suggestion on the possible influence of Pauli blocking in the fusion dynamics.

Indeed in many  heavier systems the hindrance effect has been recognized with different features depending on the various couplings to the inelastic and transfer channels. When transfer channels with positive Q-value are available, their effect is often important at low energies where it can compete with hindrance.

The case of 40Ca+96Zr will be shown as a typical example of this behavior, where the hindrance effect does not show up. We are scheduling an experiment on the “classical” case of 58Ni+64Ni to check that  the availability of several Q> 0 states following transfer effectively counterbalances the hindrance phenomenon.