A new milestone in nuclear physics has been achieved with the direct observation of three different deformations in the atomic nucleus of lead-190 (190Pb). These deformations, associated with three distinct shapes–spherical, oblate (resembling a tomato), and prolate (similar to a watermelon)–exist simultaneously near the ground state. The findings, published in Communications Physics in January 2025, were made possible by complementary experimental techniques and call for better theoretical models.
While the coexistence of different shapes in atomic nucleus has been known for over six decades, the measurement of three coexisting deformations has remained elusive. The research team, led by scientists from the University of Jyväskylä (Finland) and the University of Liverpool (UK), used advanced techniques to identify γ rays emitted in the relaxation of nuclear states, directly linking them to specific shape configurations. These measurements confirmed the prolate nature of one excited band, reassigned the lowest-lying band to an oblate shape (challenging earlier studies that suggested a spherical configuration), and identified a candidate for the first spherical excited state.
190Pb is one of the most intriguing nuclei we have studied, says Adrian Montes Plaza , dual-doctorate researcher at the University of Liverpool and the University of Jyväskylä, who analysed the data. Not only does it showcase multiple coexisting shapes, but our findings also suggest it could serve as a textbook example of nuclear states with wave functions significantly mixing contributions from each of these shapes.
Revealing the mysteries of 190Pb
The experiments were conducted at the Accelerator Laboratory of the University of Jyväskylä, where three advanced techniques were used to study the properties of 190Pb. The first measured γ rays and conversion electrons emitted immediately after its synthesis at the production target.
The second focused on γ rays emitted following the de-excitation of a metastable state. The third technique determined the lifetimes of excited nuclear states exploiting the Doppler effect, providing crucial insights into the collectivity of different configurations.
Combining multiple experimental techniques is proving to be a powerful approach for exploring rare nuclear phenomena, explains Senior Researcher Janne Pakarinen, the corresponding author. Each method provides complementary information, allowing us to build a better picture of the configuration mixing in 190Pb.
Theoretical advances through rare nuclei
The study also highlights the importance of rare nuclei like 190Pb in advancing theoretical models. Shape coexistence presents a significant challenge for nuclear theory to accurately describe complex quantum phenomena. The results from 190Pb provide an important benchmark for state-of-the-art models, offering new constraints to refine our understanding of the nuclear interaction.
Communications Physics
Experimental study
Not applicable
Direct measurement of three different deformations near the ground state in an atomic nucleus
3-Jan-2025