Fusion Hindrance and Quasi-Fission in ^<48>Ca Induced Reactions

概要

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Fusion-fission and fusion-evaporation cross sections have been measured in a large energy range for the ^<48>Ca+^<168>Er,^<154>Sm reactions. The comparison of the reduced evaporation data for such reactions and for collisions induced by light projectiles leading to the same compound nuclei ^<216>Ra^* and ^<202>Pb^* puts in evidence a fusion hindrance, which is particularly large for the first composite system. This fusion suppression is consistent with a noticeable contribution coming from quasi-fission events observed in the mass-energy distribution of fission fragments. The asymmetric shape of the quasi-fission component has been explained in terms of shell effects in the exit channel, favouring the population of closed shell fission fragments. The comparison of ^<48>Ca+^<154>Sm with preliminary data on ^<48>Ca+^<144>Sm seems to suggest that the target deformation plays a role in the onset of the quasi-fission mechanism.
2004-07-30