DATE2025.06.02 #Press Releases

The Shape of Atomic Nuclei Is "Almond-Shaped"

— Overturning the Conventional Picture to Reveal the True Shape After 70 Years —

Summary

A research group led by Dr. Takaharu Otsuka, Visiting Chief Scientist at the RIKEN Nishina Center for Accelerator-Based Science (Professor Emeritus at the University of Tokyo), Dr. Yusuke Tsunoda, Project Researcher at the Center for Nuclear Study, School of Science, The University of Tokyo, and Associate Professor Noritaka Shimizu of the Center for Computational Sciences, University of Tsukuba, has presented a new theoretical picture for the shape and rotation of atomic nuclei based on quantum theory.

This achievement challenges the conventional view of nuclear shapes and rotations that has been accepted for about 70 years, and it may ultimately lead to revisions in textbook descriptions.

Most atomic nuclei are not spherical but rather deformed into ellipsoidal shapes. Until now, it has been believed that nuclei with large deviations from spherical symmetry exhibit axially symmetric, rugby-ball-like deformations, with one circular cross-section.

In this study, the researchers, grounded in quantum theory and the nature of nuclear forces, have elucidated the shapes behavior of atomic nuclei. They theoretically demonstrated that many atomic nuclei exhibit triaxial asymmetric deformation—an “almond-shaped” ellipsoid in which all three principal axes have different lengths and no cross-section is circular. Simulations performed on the supercomputer Fugaku confirmed that the results are in accordance with this almond-shaped picture and match existing experimental data.

This research represents a major shift from the long-held understanding of nuclear deformation and is expected to contribute to future investigations, such as the search for stable superheavy elements.

The study was published in the academic journal European Physical Journal A on June 2 (Japan time).

Figure: Conventional rugby ball-shaped nucleus (b) and almond-shaped nucleus (c) of this research result

Related Links

RIKEN, University of Tsukuba

Journals

Journal name	European Physical Journal A
Title of paper	Prevailing Triaxial Shapes in Atomic Nuclei and a Quantum Theory of Rotation of Composite Objects