Nuclear descent from the fission barrier in the presence of long--range memory effects

Abstract

We have investigated the peculiarities of nuclear descent from a parabolic fission barrier within a generalized Langevin equation with power--law $f(t-t^{\prime })=(|t-t^{\prime }|/\tau {)}^{-\alpha }$ memory function. We have observed much stronger slowing down of the nuclear descent in the presence of long--range memory effects, caused by the power--law memory function at $0<\alpha <1$, than in the presence of short--range memory effects, generated by exponential $f(t-t^{\prime })=\exp (-|t-t^{\prime }|/\tau )$ memory function. At a specific value of the exponent $\alpha =1/2$ of the power--law memory function, it turned out possible to find analytically the trajectory of the descent and demonstrate that the long--range memory effects give rise to complex time oscillations of nuclear shape, becoming more frequent and damped with the correlation time $\tau$. We have found fairly long ($>10^{-20}\mathrm{s}$) times of the descent of ${}^{236}\mathrm{U}$ at the values of the correlation time $\tau \sim [10^{-24}÷10^{-23}]\mathrm{s}$.