Sub-barrier fusion of 37 Cl + 7 0 , 7 2 , 7 3 , 7 4 , 7 6 Ge

Fusion excitation functions were obtained for ${}^{37}\mathrm{Cl}{+}^{70,72,73,74,76}\mathrm{Ge}$ at energies from about 6 MeV below to 7 MeV above the Coulomb barrier. The barrier parameters extracted from the data agree within 3% with those obtained from the systematics for fusion above the barrier. Low-energy enhancements are observed, whose behavior is explained within the context of simple model calculations by assigning appropriate degrees of freedom to the respective reaction partners. These degrees of freedom reflect the shape transition between spherical ${}^{70,72,73}\mathrm{Ge}$ and prolate-deformed ${}^{74,76}\mathrm{Ge},$ and show also remarkable effects of the odd-$A$ structure of ${}^{73}\mathrm{Ge}.$ The results are consistent with those of similar analysis of different data sets where the same targets were used. The possible effects of double identical-phonon states for spherical nuclei, hexadecapole deformations for deformed ones, and nucleon transfer are also examined. An analysis of the barrier distributions is made, which indicates consistency with the assumed degrees of freedom.