Correlated transitions in TKE and mass distributions of fission fragments described by 4-D Langevin equation

TL;DR

This study uses a 4-D Langevin model to analyze fission fragment distributions, revealing correlated transitions in fission modes and symmetric modes across actinides and trans-actinides, explaining empirical twin transitions.

Contribution

First dynamical model explanation of correlated twin fission mode transitions using a consistent shape parameter approach across a wide mass region.

Findings

Symmetric mode transitions from super-long to super short around $^{254}$Es.

Dominant fission modes are mostly asymmetric, with exceptions at specific isotopes.

Twin transitions emerge naturally from 4-D potential energy surface dynamics.

Abstract

We have decomposed to symmetric and asymmetric modes the mass-TKE fission fragment distributions calculated by 4-dimensional Langevin approach and observed how the dominant fission mode and symmetric mode change as functions of $Z^2/\sqrt[3]{A}$ of the fissioning system in the actinides and trans-actinide region. As a result, we found that the symmetric mode makes a sudden transition from super-long to super short fission mode around $^{254}$Es. The dominant fission modes on the other hand, are persistently asymmetric except for $^{258}$Fm, $^{259}$Fm and $^{260}$Md when the dominant fission mode suddenly becomes symmetric although it returns to the asymmetric mode around $^{256}$No. These correlated "twin transitions" have been known empirically by Darleane Hoffman and her group back in 1989, but for the first time we have given a clear explanation in terms of a dynamical model of nuclear fission. More specifically, since we kept the shape model parameters unchanged over the entire mass region, we conclude that the correlated twin transition emerge naturally from the dynamics in 4-D potential energy surface.