STRONG DEPENDENCE OF SUBBARRIER FUSION ON THE NUCLEAR HEXADECAPOLE DEFORMATION

Fusion cross-sections sigma for the reaction W-186 + O-16 have been me asured with high precision at small energy intervals, for energies E s panning the barrier region. The distribution of fusion barriers, deriv ed from the curvature of Esigma, has the shape expected classically fr om a target nucleus with a negative hexadecapole deformation. Comparis on with the previously measured distribution for Sm-154 + O-16 demonst rates the strong sensitivity of fusion to the hexadecapole deformation . The magnitudes of the deformation parameters for W-186, extracted us ing a purely geometrical description, are different from those determi ned from non-fusion measurements. This is interpreted as reflecting th e sensitivity of the excitation function to small additional couplings .