Fusion hindrance in reactions with very heavy ions: Border between normal and hindered fusion

Abstract

The fusion hindrance in heavy-ion collisions is studied in the framework of the two-center liquid drop model. It appears that the neck and the radial degrees of freedom might both be hampered by an inner potential barrier on their path between the contact configuration to the compound nucleus. Heavy-ion reactions with and without the two kinds of fusion hindrance are classified through systematic calculations. It is found that the number of reactions without radial fusion hindrance is much smaller than that without neck fusion hindrance, and for both kinds of fusion hindrance the number of reactions without fusion hindrance at small mass-asymmetry parameter $\ensuremath{\alpha}$ is smaller than that at large $\ensuremath{\alpha}$. In the formation of a given compound nucleus, if a reaction with ${\ensuremath{\alpha}}_{c}$ is not hindered, then other reactions with $\ensuremath{\alpha}>{\ensuremath{\alpha}}_{c}$ are also not hindered, as is well known experimentally.