New pre-scission neutron multiplicity (v~") data for Li-, ' 0-, and Ne-induced fission are presented, spanning a fissility range from 0.60 to 0.85. Fission time scales have been deduced for two extreme assumptions regarding the mean excitation energy during fission. It is found for fusion-fission reactions that the fission time scale is independent of fissility, within a factor 1.5. A comparison of time scales deduced from v~"measurements for fast-fission with quasifission timescales deduced from the rotation angle of the composite system allows a minimum fusion-fission time scale of 30X10 ' s to be determined. For the most fissile system, fast-fission (fission without barrier) is shown to be up to three times faster than fusion-fission. Using a model to interpret the fusion-fission time scales, it is concluded that motion in the fission direction is strongly overdamped. This means that the dynamics of fission are dominated by a slow di6'usion towards scission, and not by the potential energy surface. It is shown that such a picture can explain the observed lack of dependence of the fission time scale on fissility.

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Preand post-scission neutron multiplicities for the reaction ' Tm(' Ar, f) at E~,b =205 MeV were measured in coincidence with fission fragments of di6'erent masses and total kinetic energies. The mass and total kinetic energy dependence of the total neutron multiplicity as well as the width of the out-of-plane fission fragment correlation angle are well described by evaporation calculations. An average time before scission of several 10 s is deduced from the average pre-scission neutron multiplicity. The mass dependence of the post-scission neutron multiplicity is consistent with an energy division at scission proportional to the mass of the fragments. For the first time clear evidence for an increase in pre-scission neutrons with increasing total kinetic energy values has been observed. Possible interpretations of this unexpected behavior are discussed.

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