Fusion hindrance for a positive Q-value system

An excitation function for the fusion reaction $^{28}\mathrm{Si}$ $+$ $^{30}\mathrm{Si}$ ($Q=14.3\mathrm{MeV}$) has been measured down to $40\ensuremath{\mu}b$. Deviations from the behavior predicted by the optical model and standard coupled-channels calculations have been observed in this system. The fusion cross sections can be reproduced by a shallow potential model well, which was originally developed to explain the hindrance of heavy-ion fusion for systems with negative $Q$-values.