Coupled-channels analysis of the ¹⁶O+²⁰⁸Pb fusion barrier distribution

Analyses using simplified coupled-channels models have been unable to describe the shape of the previously measured fusion barrier distribution for the doubly magic ¹⁶O+²⁰⁸Pb system. This problem was investigated by remeasuring the fission excitation function for ¹⁶O+²⁰⁸Pb with improved accuracy and performing more exact coupled-channels calculations, avoiding the constant-coupling and first-order coupling approximations often used in simplified analyses. Couplings to the single- and 2-phonon states of ²⁰⁸Pb, correctly taking into account the excitation energy and the phonon character of these states, particle transfers, and the effects of varying the diffuseness of the nuclear potential, were all explored. However, in contrast to other recent analyses of precise fusion data, no satisfactory simultaneous description of the shape of the experimental barrier distribution and the fusion cross sections for ¹⁶O+²⁰⁸Pb was obtained.