Nuclei of Atoms Can Be Pear-Shaped, Says Physicist

In chemistry and physics textbooks, the core, or nucleus, of atoms is almost always depicted as spherical in shape. In reality, atomic nuclei can be in a variety of shapes, such as flattened or stretched spheres. In fact, new research has found “strong circumstantial evidence” for an even more exotic, asymmetrical form: a pear-shaped nucleus.

“Although the existence of pear-shaped nuclei has been predicted for a long time, many of those anticipated to be the best candidates do not occur as stable nuclei in nature, so they have to be synthesized in a nuclear reaction before study,” wrote physics Prof. Christopher J. “Kim” Lister in a commentary published in the May 9 issue of the journal Nature.

Lister, who is co-director of UMass Lowell’s Radiation Laboratory, was invited to give his expert opinion on the recent confirmation of the elusive pear-shaped nuclei made by an international team of physicists working at the CERN lab in Geneva, Switzerland. The team’s findings, along with Lister’s comments and those from a researcher from University College London, were featured as the cover story for that issue of Nature.

By firing accelerated beams of heavy, radioactive ions at a thick piece of uranium carbide, researchers from the University of Liverpool in the U.K. and other countries studied short-lived, unstable isotopes of radon and radium and found clear, tell-tale radiation signatures of a pear shape in the radium-224 nucleus.

The results of the experiments have significant implications both for the understanding of the nuclear structure as well as for investigations beyond the standard model of particle physics.

“With new accelerators being built around the world with the aim of producing beams of exotic isotopes, and ever more sensitive detectors for measuring electromagnetic radiation patterns, we can expect more of this ‘isotope tailoring,’ ” noted Lister in the Nature article. “By picking out special and interesting features for study, these methods will allow us to gain a more profound understanding of how all nuclei really work.”

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