Asish K. Dhara

A Dynamical study of fission process and estimation of prescission neutron multiplicity

The dynamics of fission has been studied by solving Euler-Lagrange equation 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.

Enhancement of signal-to-noise ratio

It is shown that the ratio of signal-to-noise ratio at the output to that at the input can be made larger than unity when a nonlinear system is subjected to a weak periodic perturbation and a harmonic noise. This theoretical result is in conformity with the experimental observation published recently by R. Liet al.

Coherent stochastic resonance in the case of two absorbing boundaries.

The coherent stochastic resonance is observed and studied with a multistep periodic signal in a continuous medium having two absorbing boundaries. The general features of this process are exhibited. The universal features at the resonance point are demonstrated. The kinetic behaviors around the resonance point are also presented.

Coherent Stochastic Resonance in One Dimensional Diffusion with One Reflecting and One Absorbing Boundaries

It is shown that the single-step periodic signal (periodic telegraph signal) can not produce coherent stochastic resonance for diffusion on a segment with one absorbing and one reflecting end points while the multi-step periodic signal does. The general features of this process are exihibited. The resonant frequency is found to decrease and the mean first passage time at resonant frequency increases linearly, as we increase the length of the medium. The cycle variable is shown to be the proper argument to express the first passage probability at resonance. A formula for first passage probability at resonance is derived in terms of two universal functions, which clearly isolates its dependence on the length of the medium.

New Characterization of Stochastic Resonance in Bistable Square Potential Well

The features of first passage time density function is analysed theoretically in a symmetric double square well system modulated periodically with a signal of arbitrary amplitude and frequency. Resonance is demonstrated as a maximum synchronization between periodic signal and noise. Resonance is characterized as a linear relation between noise strength at resonance and frequency. This characterization is shown to hold good for amplitude lesser or greater than the depth of the unmodulated potential well. The mean first passage time of the process at resonance is also shown to decrease linearly with the strength of the noise for high amplitude of the signal while it increases linearly with inverse of the noise strength for low amplitude.

Synchronization Under Periodic Modulation of Symmetric Double Square Wells in a Bistable Stochastic System

The features of the first-passage-time density function are analyzed theoretically in terms of synchronization between noise and periodic signal in a symmetric double-square-well system. Resonance is demonstrated as a maximum synchronization between them. To have the maximum cooperation between signal and noise, it is shown that the noise strength at resonance should increase linearly with the frequency of the signal. The time scale of the process at resonance is also shown to increase linearly with the period of the signal.

Dissipative dynamics of fission in the framework of asymptotic expansion of Fokker-Planck equation

Abstract: The dynamics of fission has been formulated by generalising the asymptotic expansion of the Fokker-Planck equation in terms of the strength of the fluctuations where the diffusion coefficients depend on the stochastic variables explicitly. The prescission neutron multiplicities and mean kinetic energies of the evaporated neutrons have been calculated and compared with the respective experimental data over a wide range of excitation energy and compound nuclear mass. The mean and the variance of the total kinetic energies of the fission fragments have been calculated and compared with the experimental values.