Quasielastic barrier distributions for the 20Ne+58,60,61Ni systems: Influence of weak channels

Background: Near-barrier fusion can be strongly affected by the coupling between relative motion and internal degrees of freedom of the collision partners. The coupled channels (CC) method is a usual way of describing the reaction dynamics in this energy region. In the standard approach in the CC method only strong reaction channels (collective excitations) are taken into account. However, in some cases this approach fails to describe experimentally obtained barrier height distributions. Purpose: The influence of weak (noncollective) reaction channels on barrier height distributions was studied. Method: The barrier height distributions were determined from quasielastic scattering of Ne-20 on Ni-58,Ni-60,Ni-61 targets. The scattered ions were registered at backward angles (130-150 degrees). Results: In the Ni-58 and Ni-60 cases one observes a structure (two peaks) in the barrier height distribution which is completely smoothed out for Ni-61. Conclusions: The results support the hypothesis that noncollective excitations of the target nuclei, much more numerous in Ni-61 than in Ni-58 and Ni-60, influence the barrier height distribution and are responsible for smoothing out the structure.