Scientists at the Bogoliubov Laboratory of Theoretical Physics, together with colleagues from research centres in the Czech Republic, Germany, Slovakia, Japan, and the United Kingdom, identified candidates for toroidal dipole excitations in the nickel-58 nucleus for the first time. The results, published in Physical Review Letters, open up new opportunities for experimental study of atomic nucleus structure and vortex excitations’ influence on heavy element nucleosynthesis.

a) schematic 3D view of currents on the surface of a torus; b) 2D cut in the x-z plane; c) theoretical prediction of the current distribution of the toroidal electric dipole mode in a nucleus

Dipole toroidal modes are a unique set of excitations that are predicted to occur in various physical systems, ranging from atomic nuclei to metamaterials. Their distinctive feature is a toroidal distribution of currents, which forms vortex-like structures similar to smoke rings. Despite the theoretical predictions made about 50 years ago, the experimental detection of these exotic modes in nuclei remains challenging due to the lack of methods for their unambiguous identification.

The key result of the researchers’ work was the detection of signatures of the toroidal mode during electron scattering under large backward angles, which confirmed their unique properties. The toroidal mode represents a new class of electric dipole excitations, along with the known non-vortex isovector and isoscalar fluctuations of protons and neutrons. The study of these modes is critically important for understanding the structure of heavy neutron-excess nuclei, in which they can influence dipole force distribution and nucleosynthesis processes.

In 2025, a new experiment is planned at the S-DALINAC Electronic Linear Accelerator at the Institute of Nuclear Physics of the Technical University of Darmstadt (IKP TU Darmstadt, Germany) to test the hypothesis of the connection of low-energy dipole resonances with toroidal excitations in neutron-excess nuclei. The data obtained may lead to a revision of a number of modern structure models.

Read more about the results of the study in the article entitled “Nickel-58 nucleus may host elusive toroidal dipole excitations” on the Phys.org. Among the authors are employees of the BLTP JINR Nuclear Structure Sector: Doctor Physics and Mathematics Valentin Nesterenko and his postgraduate student from Kazakhstan Petr Vishnevskiy.