The dynamics of fission has been studied by solving Euler-Lagrange equations with dissipation generated through one and two body nuclear friction. The average kinetic energies of the fission fragments, prescission neutron multiplicities and the mean energies of the prescission neutrons have been calculated and compared with experimental values and they agree quite well. A single value of friction coefficient has been used to reproduce the experimental data for both symmetric and asymmetric splitting of the fissioning systems over a wide range of masses and excitation energies. It has been observed that a stronger friction is required in the saddle to scission region as compared to that in the ground state to saddle region.

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Prescission neutron multiplicities have been calculated in the framework of a simple, dynamical model of fission. The fission trajectories have been calculated by solving Euler-Lagrange equations with dissipation generated through two-body nuclear viscosity. Systematic study of the relationship between the prescission neutron multiplicities and nuclear viscosity has been made in the range of mass 150-200 and incident energy 4 -13 MeV/nucleon. The values of the viscosity coefficients which are used to predict the observed prescission neutron multiplicities follow a global relation in the region of mass and energy studied.PACS number͑s͒: 25.70.Jj, 24.75.ϩi, 25.70.Gh

The inclusive energy distributions of fragments with Z ≥ 3 emitted from the bombardment of 12 C by 20 Ne beams with incident energies between 145 and 200 MeV have been measured in the angular range θ lab ∼ 10 • -50 • . Damped fragment yields in all cases have been found to be characteristic of emission from fully energy equilibrated composites; for B, C fragments, average Q-values, < Q >, were independent of the centre of mass emission angle (θc.m.), and the angular distributions followed ∼1/sinθc.m. like variation, signifying long life times of the emitting di-nuclear systems. Estimation of total yields of these fragments have been found to be much larger compared to the standard statistical model predictions of the same. This may be indicative of the survival of orbiting like process in 12 C + 20 Ne system at these energies.

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