Fusion barriers,empirical and theoretical: Evidence for dynamic deformation in subbarrier fusion

Semiempirical fusion barriers have been obtained by analysis of 87 excitation functions for complete fusion. These barriers are used as a test for several theoretical potentials. For most of the reactions at energies below the operational s-wave fusion barrier, the cross sections are greater than expected from considerations of simple barrier penetration alone. We ascribe this to dynamic effects, such as neck formation which may be expected as precursors of fusion. The effects of static deformation do not appear to be sufficient to explain the discrepancies.