Energy dissipation and suppression of capture cross sections in heavy ion reactions

Background: At energies above the capture barrier, coupled-channels (CC) calculations with a standard nuclear potential diffuseness (0.65 fm) increasingly overestimate experimental cross section as charge product (${Z}_{1}{Z}_{2}$) of colliding nuclei increases. It has been suggested this may be linked to energy dissipation outside barrier.Purpose: We investigate quantitatively role in suppressing heavy ion fusion reactions.Method: The yields sequential fission, including that resulting from deep inelastic collisions, and fission following were determined simultaneously for collisions $^{18}\mathrm{O}, ^{30}\mathrm{Si}, ^{34}\mathrm{S}$, $^{40}\mathrm{Ca}+^{232}\mathrm{Th}$ at range around respective barriers.Results: ratio CC sections was found decrease increasing ${Z}_{1}{Z}_{2}$. Conversely, capture-fission increased sum agrees quite well sections.Conclusions: sections, their comparison calculations, give consistent picture increase density overlap barrier ${Z}_{1}{Z}_{2}$ is correlated dissipative processes. These compete strongly reaction For $^{40}\mathrm{Ca}$ reaction, total yield exceeds expectations model indicating processes occur both trajectories would have led also more peripheral trajectories.