Observation of sub-barrier fusion enhancement due to negative hexadecapole deformations?

Abstract

Fusion excitation functions for 16O on 176,180Hf and 182,184,186W have been measured over an energy range spanning the fusion barrier. Contrary to expectation, the sub-barrier cross sections are systematically lower for the nuclei with larger quadrupole deformations, beta 2. These cross sections are also significantly higher than those calculated using a model which takes beta 2 deformations into account; similar comparisons for other reactions, including 16O on 152,154Sm, show no such enhancement. The authors suggest that fusion enhancement due to the negative hexadecapole deformations of the Hf and W nuclei may have been observed for the first time.