Pear-Shaped Atomic Nuclei Offer Window into Nature’s Symmetries
- MM24 News Desk
- 56 minutes ago
- 2 min read
The collinear resonance ionisation spectroscopy (CRIS) apparatus at the ISOLDE facility. (Image: CERN)
A new study at CERN’s ISOLDE facility has brought fresh insight into one of the most intriguing shapes in nuclear physics — the pear-shaped nucleus. The discovery, recently published in Science, sheds new light on how such asymmetric nuclei could help scientists probe the deepest symmetries of the universe.
Most atomic nuclei are perfectly round or shaped like elongated rugby balls. Yet a select few take on a rare pear-like form, heavier at one end than the other. This imbalance, while subtle, may hold the key to uncovering phenomena beyond the Standard Model of particle physics — the framework that currently describes all known particles and forces.
At ISOLDE, researchers from an international collaboration studied a molecule containing one such nucleus: radium monofluoride (²²⁵Ra¹⁹F). This is the same facility where pear-shaped nuclei were first identified, making it an ideal place to delve deeper into their unusual properties.
Using a blend of advanced theory and high-precision experiments, the team uncovered new details about the molecule’s energy-level structure — the quantum “rungs” that define how its electrons and nucleus interact. These energy levels, and the extremely fine splittings between them, are exquisitely sensitive to potential new forces or particles that may lie beyond current physics.
“Molecules like ²²⁵Ra¹⁹F are remarkable tools,” explained lead researcher Shane Wilkins. “They amplify the subtle effects of symmetry violations, allowing us to search for signs of new physics that remain invisible elsewhere.”
But studying such exotic systems is far from simple. The ²²⁵Ra nucleus is radioactive, giving the molecule a fleeting lifespan of just 20 days. Researchers must create these molecules in the lab and study them quickly before they decay. Moreover, interpreting the data requires cutting-edge quantum calculations to understand how the pear-shaped nucleus affects its surrounding electrons.
The ISOLDE team achieved this through meticulous measurements of the molecule’s hyperfine structure — the ultra-fine splitting of energy levels caused by the interaction between the nucleus and the magnetic field of its electrons. Using the collinear resonance ionisation spectroscopy (CRIS) apparatus, they directed three synchronized laser pulses onto the molecules, teasing out precise information about these interactions.
The results revealed how the asymmetric spread of magnetism within the ²²⁵Ra nucleus subtly shifts the molecule’s energy levels — a phenomenon previously observed in atoms but never before in a molecule.
“This is the first time we’ve observed such magnetic effects from a pear-shaped nucleus within a molecular system,” said Wilkins. “It’s a crucial step toward using these molecules to test the fundamental symmetries of nature and search for physics beyond the Standard Model.”
By deepening our understanding of these delicate quantum interactions, the study not only strengthens future experimental designs but also paves the way for uncovering hidden patterns in the laws that govern the universe.
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