Fission dynamics at low excitation energy. 2

TL;DR

This paper investigates low-energy fission of U-236, revealing that shell effects influence fragment mass distribution peaks, while shape fluctuations near scission determine peak widths, offering a new perspective on fission dynamics.

Contribution

It introduces a novel analysis of fission trajectories showing the importance of shape fluctuations and shell effects in fission fragment distributions.

Findings

Mass distribution peaks are shaped by saddle point shell effects.

Width of peaks results from shape fluctuations near scission.

Fission involves shape fluctuations between elongated and compact forms.

Abstract

The mass asymmetry in the fission of U-236 at low excitation energy is clarified by the analysis of the trajectories obtained by solving the Langevin equations for the shape degrees of freedom. It is demonstrated that the position of the peaks in the mass distribution of fission fragments is determined mainly by the saddle point configuration originating from the shell correction energy. The width of the peaks, on the other hand, results from the shape fluctuations close to the scission point caused by the random force in the Langevin equation. We have found out that the fluctuations between elongated and compact shapes are essential for the fission process. According to our results the fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup, but is accompanied by the fluctuations between elongated and compact shapes. This picture presents a new viewpoint of fission dynamics and the splitting mechanism.