Fission rate of excited nuclei at variable friction in the energy diffusion regime (original) (raw)
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Dissipative dynamics of nuclear fission is a well confirmed phenomenon described either by a Kramers-modified statistical model or by a dynamical model employing the Langevin equation. Though dynamical models as well as statistical models incorporating fission delay are found to explain the measured fission observables in many studies, it nonetheless shows conflicting results for shell closed nuclei in the mass region 200. Analysis of recent data for neutron shell closed nuclei in excitation energy range 40−80 MeV failed to arrive at a satisfactory description of the data and attributed the mismatch to shell effects and/or entrance channel effects, without reaching a definite conclusion. In the present work we show that a well established stochastic dynamical code simultaneously reproduces the available data of pre-scission neutron multiplicities, fission and evaporation residue excitation functions for neutron shell closed nuclei 210 Po and 212 Rn and their isotopes 206 Po and 214,216 Rn without the need for including any extra shell or entrance channel effects. The calculations are performed by using a phenomenological universal friction form factor with no ad-hoc adjustment of model parameters. However, we note significant deviation, beyond experimental errors, in some cases of Fr isotopes.
Nuclear Physics A, 1984
Nuclear fission is described as a transport process over the fission barrier. The fission width is obtained from the time dependent probability flow over the saddle point. Its relation tith the Bohr-Wheeler formula is discussed in the case where asymptotically in time a quasistationary flow exists. Inthe converse situation the whole fission process becomes a transient phenomenon. In both cases the duration time T of the transient process is defined and semi-quantitative analytical estimates are derived and compared with direct numerical evaluations. It is shown that the effect of the finiteness of T has direct consequences on the neutron multiplicities resulting from a cascade de-excitation of a compound nucleus in a situation where the current would reach asymptotically a quasistationary regime at all steps of the de-excitation chain. With respect to predictions of the statistical model, enhancement of these multiplicities by factors 2 to 5 are obtained in the excitation energy range 100 to 200 MeV depending on the value of the nuclear friction 8.
Dynamical study of fission process and estimation of prescission neutron multiplicity
Physical Review C, 1998
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.