Insight into the effects of shell structure on the fusion of mid-mass nuclei using isotopic chains of K and Ar nuclei on a Si target

The effects of neutron shell closures on fusion are investigated through measurement of the fusion excitation functions for ^36,44Ar/^39,41,45,47K + ²⁸Si.  At above barrier energies, differences in the measured cross-sections are understood by creating a reduced excitation function which accounts for the size and barriers of the fusing systems.  At energies below the Coulomb barrier, however, large enhancement of the cross-section for open-shell projectiles over the closed-shell projectiles is observed.   Coupled channel calculations using Dirac-Hartree-Bogoliubov (DHB) densities provide a good description for the closed-shell nuclei but fail to describe the open-shell nuclei.  The influence of the target nucleus is explored through comparison of this data to measured cross-sections for the same projectiles on an ¹⁶O target.