Fission process of low excited nuclei with Langevin approach

TL;DR

This paper uses a Langevin dynamical model to accurately reproduce the asymmetric fission fragment mass distributions of U and Pu isotopes at low excitation energies, highlighting the importance of shell effects and dissipation.

Contribution

It demonstrates, for the first time, that the Langevin approach can reproduce experimental mass distributions without parameter adjustment, emphasizing the role of shell effects and dissipation.

Findings

Reproduced asymmetric mass distributions without parameter tuning.

Shell effects dominate the potential energy landscape.

Dissipation influences fluctuations and pre-scission neutron multiplicities.

Abstract

Fragment mass distributions from the fission of U and Pu isotopes at low excitation energies are studied using a dynamical model based on the fluctuation-dissipation theorem formulated as Langevin equations. The present calculations reproduced the overall trend of the asymmetric mass distribution without parameter adjustment for the first time using the Langevin approach. The Langevin trajectories show a complicated time evolution on the potential surface, which causes the time delay of fission, showing that dynamical treatment is vital. It was found that the shell effect of the potential energy landscape has a dominant role in determining the mass distribution, although it is rather insensitive to the strength of dissipation. Nevertheless, it is essential to include the effect of dissipation, since it has a crucial role in giving "fluctuation" to Langevin trajectories as well as for explaining the multiplicities of pre-scission neutrons as the excitation energy increases. Therefore, the present approach can serve as a basis for more refined analysis.