Scientist-theorists at the National Centre for Nuclear Research have just published the results of a detailed analysis of the mechanisms of heavy ion fusion reactions, key to the synthesis of new elements. The research, based on an advanced multivariate approach using stochastic dynamics, sheds new light on the process of forming complex atomic nuclei.

Heavy-ion fusion is a process in which two heavy atomic nuclei combine to form a new, heavier nucleus. It is a method used in laboratories to synthesise elements with high atomic numbers, including superheavy elements. Understanding the mechanisms involved in this process is key to optimising the conditions leading to successful synthesis. Recent decades have seen tremendous progress in the synthesis of superheavy nuclei, but the basic reaction mechanisms that lead to their production are still not fully understood by researchers. This is particularly true for the cold fusion reaction mechanisms, especially its intermediate phase, which plays a key role in the success of the whole process.

Dissipative dynamics formalisms such as the Langevin and Fokker-Planck equations have proved to be powerful tools for investigating these challenges. They allow phenomena such as heavy-ion reactions or nuclear fission to be modelled accurately, and also provide insights into experimental observables such as evaporation residue cross sections for deeply inelastic reactions, energy dissipation and mass and charge transfer. Furthermore, they can be successfully applied to the description of quasi-fission, resulting in the precise reconstruction of mass distributions of fission products.

"In our study, we analysed in detail the stages that an atomic system goes through during fusion before a new nucleus is formed" - explain the NCBJ authors. "The Langevin formalism used, which takes into account frictional effects and energy fluctuations, has allowed us to better understand the dynamics of this process. The results show the important role of the damped state in the stabilisation of the nuclear neck, as well as the interplay between the shape and rotation degrees of freedom."

The analyses performed showed excellent agreement with experimental data on spin distribution and fusion evaporation residue cross sections. This provides a solid basis for further research into superheavy element fusion and the exploration of fusion inhibition mechanisms. Understanding these mechanisms can contribute to the development of more efficient strategies for the synthesis of new elements, which is one of the most important challenges in modern nuclear physics.

The results of the study were published in the paper: Y. Jaganathen, M. Kowal and K. Pomorski, Demystifying the fusion mechanism in heavy-ion collisions: A six-dimensional Langevin dissipative dynamics approach, Physics Letters B, 139302, https://doi.org/10.1016/j.physletb.2025.139302