Fusion dynamics around the Coulomb barrier

Abstract

We perform exact coupled-channels calculations, taking into account properly the effects of Coulomb coupling and the finite excitation energy of collective excitations in the colliding nuclei, for three Fm formation reactions, ${}^{37}$Cl + ${}^{209}$Bi, ${}^{45}$Sc + ${}^{197}$Au, and ${}^{59}$Co + ${}^{181}$Ta. For the ${}^{37}$Cl + ${}^{209}$Bi and ${}^{45}$Sc + ${}^{197}$Au reactions, those calculations well reproduce the experimental total fission cross sections, and a part of the extra-push phenomena can be explained in terms of the Coulomb excitations to multi-phonon states. On the other hand, for the heaviest system, the deep-inelastic collisions become much more significant, and the fission cross sections are strongly overestimated. We also discuss the surprisingly large surface diffuseness parameters required to fit recent high-precision fusion data for medium-heavy systems, in connection with the fusion supression observed in massive systems.

Comments: 10 pages, 6 ps figures. Uses aipxfm.sty. A talk given at the Tours Symposium on Nuclear Physics V, August 26 - 29, 2003, Tours, France