Anomalous anisotropies of fission fragment angular distributions in sub-barrier fusion-fission reaction

Fission cross sections and angular distributions have been measured for the 19F+232Th reaction at energies ranging from 0.8 to 1.1 of Coulomb barrier. For the first time it has been observed that the anisotropies as a function of the center-of-mass energy show a bump around 84 MeV, while the excitation function varies monotonically. The excitation function can be reproduced in the framework of the coupled channels theory. However, the models fail to account for the experimental anisotropies, especially of the bump. (orig.)