Recent experimental results for the fusion of the proton-halo system ${}^8\text{B}+{}^{58}\text{Ni}$ are discussed. A strong enhancement is observed both below and above the barrier. This is qualitatively different from the usual sub-barrier enhancement observed for many heavy-ion systems. Arguments are given that relate the enhancement to a static halo effect directly associated to the extended size of the proton-halo state. A simple single-barrier model is proposed which describes the fusion cross sections in terms of a maximum angular momentum for fusion, $L_f$. It is shown that a linear energy dependence for $L_f$ gives a surprisingly good description of the experimental fusion excitation function not only for ${}^8\text{B}+{}^{58}\text{Ni}$ but also for the neutron-halo systems ${}^6\text{He}+{(}^{209}\text{Bi},{}^{64}\text{Zn})$. The model is also applied to several weakly bound systems.

• Received 9 December 2011

DOI:https://doi.org/10.1103/PhysRevC.85.014603