Fusion hindrance of heavy ions: Role of the neck

Fusion of heavy ions is largely hindered because of the appearance of an inner barrier between the contact point of the two colliding nuclei and the compound nucleus. But there are still quantitative ambiguities on the size of the barrier and on the role of the dissipation. In this paper we stress the importance of the neck of the composite system on the hindrance of the fusion of heavy nuclei. We show that the ''denecking'' process is very quick compared to the other collective degrees of freedom as the relative distance. This behavior of the neck will change the potential seen by the relative distance on the way to fusion and its effective initial value through a dynamical coupling. Both effects contribute to the hindrance of fusion.