Fusion-Fission versus Quasifission: Effect of Nuclear Orientation

Fission fragment angular distributions and cross sections have been measured for the reaction of ¹⁶O+²³⁸U at energies around the Coulomb barrier. Full momentum transfer events were selected using the folding angle technique. The fission fragment anisotropies rise rapidly as the beam energy decreases through the barrier region. This is interpreted as showing that collisions with the tips of the deformed target nucleus lead to quasifission, collisions with the sides to fusion-fission.