Influence of additional neutrons on the fusion cross-section beyond the N=8 shell

Fusion enhancement for neutron-rich isotopes of oxygen on carbon nuclei was probed. To measure the fusion cross-section a ${}^{20}$O beam accelerated to E${}_{lab}$/A=2.7 MeV bombarded the active-target detector MuSIC@Indiana with a fill gas of CH${}_4$. Examination of the average fusion cross-section over the interval 12 MeV $\le$E${}_{c\mathrm{.}m\mathrm{.}}$$\le$ 17 MeV for ${}^{16-20}$O + ${}^{12}$C reveals that while even isotopes of oxygen exhibit essentially the same cross-section, the cross-section for odd isotopes can be either enhanced or suppressed relative to the even A members of the isotopic chain. Theoretical models fail to explain the observed experimental results.