New Model Cracks Code of Mercury Fission

Scientists have created a groundbreaking model accurately mirroring the fission process in mercury isotopes, potentially rewriting our understanding of nuclear behavior. This innovative approach provides unprecedented insight into atomic nuclei, challenging existing theories and paving the way for enhanced predictive models.

Unraveling Mercury’s Secrets

An international research team, including scientists from Science Tokyo, has devised a five-dimensional Langevin model. The model can precisely reproduce the fission fragment distributions and kinetic energies of mercury isotopes, like 180Hg and 190Hg, according to the recent research.

The approach uniquely captures the unusual, double-humped mass distribution seen in mercury-180. This finding indicates that nuclear shell effects influence fission dynamics even at higher excitation energies. Earlier models had failed in accurately explaining the process of mercury’s asymmetric fission.

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By demonstrating that these structural effects persist beyond heavy elements like uranium and plutonium, the findings enhance the understanding of nuclear fission processes. In 2024, nuclear energy provided approximately 10% of the world’s electricity, highlighting its continued importance in the global energy mix (World Nuclear Association).

Deeper Dive into Nuclear Fission

The researchers, under the guidance of Associate Professor Chikako Ishizuka at the Institute of Zero-Carbon Energy, Science Tokyo, formulated the five-dimensional Langevin model. This study, published in Physical Review C on May 20, 2025, has been recognized as an Editor’s Suggestion by the journal.

Unlike the well-understood fission of heavy elements, the splitting of lighter nuclei, such as mercury, has remained largely mysterious. Experiments have revealed that mercury-180 undergoes an unexpected asymmetric fission, creating fragments of varying sizes. These surprising results have challenged current theories.

The Langevin model tracks the dynamic shape of the nucleus in real time. This dynamic analysis begins with its initial state of equilibrium and continues to the moment of scission, when it splits into smaller components. Developing accurate models for these lighter elements is critical, because their behavior often diverges from that of well-studied heavy isotopes.

Key Model Enhancements

A soft wall was integrated into the model, located at the edges of the deformation space. This soft wall allowed the model to simulate how the nucleus alters its shape during fission. The researchers also considered how shell effects shift with increasing excitation energy, a factor often oversimplified in earlier models.

The simulation closely matched experimental results for the fragment mass distributions and kinetic energy. For 180Hg, it accurately recreated the observed double-peaked mass pattern. Shell effects were found to remain significant even at higher excitation energies of 40–50 MeV, contradicting previous beliefs.

The researchers also considered multichance fission, where the nucleus releases neutrons before splitting. This had little impact on fragment masses at low energies. However, it strongly affects total kinetic energy, making TKE a useful tool for studying multichance fission.

According to Ishizuka, these findings offer valuable new insights into the fission process. The research confirms the effectiveness of the 5D Langevin approach in accurately predicting key fission observables.