Sub-barrier fusion ofAl27+70,72,73,74,76Ge: Evidence for shape transition and structure effects

Abstract

Fusion excitation functions were obtained for $^{27}\mathrm{Al}$${+}^{70,72,73,74,76}$Ge at energies from about 6 MeV below to 7 MeV above the Coulomb barrier. One-dimensional barrier penetration model calculations with one free parameter yield parameters in good agreement with the systematics for fusion above the barrier. Large low-energy enhancements are observed whose trend suggests the presence of a structural change between $^{70,72}\mathrm{Ge}$ and $^{73,74,76}\mathrm{Ge}$. Within the context of simple model calculations, this trend is explained as arising from the odd-A structure of $^{73}\mathrm{Ge}$ on one hand, and from a spherical (or oblate) to prolate shape transition between $^{70,72,73}\mathrm{Ge}$ and $^{74,76}\mathrm{Ge}$, on the other hand.