Global Increase of Near- and Below-Barrier Fusion for Heavier Systems

Twenty excitation functions for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$-, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$-, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$-, and ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$-induced fusion were deduced from measured neutron production cross sections. A global increase of the near-barrier fusion is observed as reactant masses increase, which by far cannot be accounted for by one-dimensional barrier penetration models. Static properties such as deformation introduce only small modifications to this tendency, whereas the mean curvature radius provides a good scaling to this phenomenon, thus indicating shape distortions or neck formation.