It is demonstrated experimentally that the reaction systems on the different side of Businaro-Gallone critical mass asymmetry (␣ BG ) have different characteristics in fusion-fission reactions. Fragment anisotropies resulting from the reactions with the entrance-channel mass asymmetry ␣Ͼ␣ BG are well described by the saddlepoint transition-state model. However, the measured fragment anisotropies for the systems with ␣Ͻ␣ BG are obviously greater than the predictions of this model at subbarrier and near-barrier energies and gradually tend to coincide with the theoretical expectations as the bombarding energy increasing over fusion barrier. These observations have led us to a suggestion of preequilibrium fission for low angular momentum. The predictions of such a preequilibrium fission model are compared with the available experimental data and it is shown that they can satisfactorily reproduce the observed trends as a function of the bombarding energy for the reaction systems studied. ͓S0556-2813͑96͒00507-9͔PACS number͑s͒: 25.70.Jj

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Excitation functions have been measured for quasielastic and elastic scattering of 16 Oϩ 152 Sm around the Coulomb barrier at three backward angles with high precision in small energy steps. The barrier distributions have been extracted from the quasielastic and elastic scattering excitation functions and compared with experimental barrier distributions obtained from the existing fusion excitation function and spin distributions for the same reaction system, and from the quasielastic and elastic scattering excitation functions for the neighboring isotope 154 Sm. The agreement is rather good. The results show clearly that the asymmetric barrier distributions are due to the effects of static deformations on the target nucleus. This is the first attempt to compare quantitatively the experimental barrier distributions with the fusion barrier distributions extracted from the spin distributions for the same system. ͓S0556-2813͑98͒50903-X͔ PACS number͑s͒: 25.70. Bc, 25.45.Hi, 25.70.Jj

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