By Dr. (Hons.) Piyush Chakraborty
D.Litt. in Astrophysics | D.Sc. (Honoris Causa) | Pursuing PhD, Kennedy University, USA
New Delhi: A detailed study of rapidly rotating atomic nuclei has offered fresh insight into the complex behaviour of rare-earth nuclei under extreme rotational conditions. The research, published in the International Journal of Nuclear Structure Physics in 2024, examines how the internal structure, shape and pairing of nucleons change as these nuclei are pushed to high angular momentum.
The study examines seven rare-earth nuclei and uses the Cranked Shell Model to understand what happens inside a nucleus when it rotates at very high speed. The researchers compared their calculations with available gamma-ray spectroscopy data.
One of the central features examined is band crossing, which can appear as a sudden change, or “backbending”, in the rotational behaviour of a nucleus. As a nucleus rotates faster, pairs of neutrons can change their alignment with the rotational axis, producing a noticeable change in angular momentum.
According to the study, the first major band crossing is associated with the alignment of a pair of high-angular-momentum i₁₃/₂ neutrons. The calculated crossing frequencies were reported to be within about ±0.02 MeV of experimental values across the seven nuclei studied.
The study also highlights the Coriolis anti-pairing effect, through which increasing rotational frequency weakens pairing correlations between nucleons. The researchers found a significant reduction in the neutron pairing gap around the band-crossing region.
Another finding is that nuclear shape can change as rotational speed increases. The calculations indicate a transition from predominantly prolate shapes at lower spin towards more triaxial configurations at higher spin.
The research also compares the standard Cranked Shell Model with a particle-number-conserving approach, with the cross-check supporting the calculated quasiparticle configurations and band-crossing behaviour.
The findings may also contribute to nuclear astrophysics, particularly models of nuclear level densities relevant to neutron-capture processes involved in the formation of heavy elements. The paper additionally discusses long-lived nuclear isomeric states, including ¹⁷⁸Hf.
Overall, the study adds to the understanding of how particle motion, nuclear pairing, shape changes and collective rotation interact inside rare-earth nuclei, while highlighting the importance of further experimental studies of nuclei under extreme rotational conditions.
