Advancing fission dynamics understanding in mercury isotopes with 5D Langevin model

Advancing fission dynamics understanding in mercury isotopes with 5D Langevin model
by Clarence Oxford
Los Angeles CA (SPX) Jun 21, 2025

A novel five-dimensional Langevin model developed by researchers from Science Tokyo and international collaborators has accurately simulated fission fragment distributions and kinetic energies in mercury isotopes 180Hg and 190Hg. This model successfully captures the anomalous double-peaked mass distribution in 180Hg and highlights the role of nuclear shell effects at elevated excitation energies.

Unlike extensively studied uranium and plutonium fission, lighter sub-lead nuclei such as mercury exhibit unexpected behaviors. Experimental observations of 180Hg revealed asymmetric fission products, challenging existing theoretical frameworks. To address this, Associate Professor Chikako Ishizuka from the Institute of Zero-Carbon Energy led a research effort to refine predictive tools for sub-lead nuclear fission.

The resulting 5D Langevin approach, published in Physical Review C and designated an Editor's Suggestion, dynamically tracks the nuclear shape evolution through deformation space up to the scission point. The research team included Dr. F. A. Ivanyuk (Institute for Nuclear Research, Ukraine), Professor C. Schmitt (University of Strasbourg, France), and Satoshi Chiba (NAT Co., Ltd., Japan).

This dynamic model goes beyond traditional static methods by incorporating both macroscopic motion and microscopic shell effects. A key enhancement is the introduction of a "soft wall" boundary, improving simulation accuracy of nuclear deformation paths. The model's realism is further strengthened by its capacity to adapt shell effects at higher excitation energies-up to 50 MeV-where earlier models presumed they would vanish.

Model predictions aligned closely with experimental data for both fission fragment masses and total kinetic energies. Specifically for 180Hg, the model reproduced the double-humped distribution observed experimentally, offering a deeper look into the mechanics of asymmetric fission. It also handled multichance fission, showing that while pre-fission neutron emission minimally alters mass distributions, it notably affects kinetic energy outputs.

"Our calculations confirm that the 5D Langevin approach is a reliable tool for theoretical predictions of fission process observables," said Ishizuka, emphasizing the model's applicability to medium-mass nuclei where traditional models fall short.

Research Report:Shell effects and multichance fission in the sub-lead region