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Physicists get a good look at pear-shaped atomic nuclei

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In schoolbook drawings, nuclei -- the protons and neutrons at the center of atoms -- are often represented as neat, spherical little bunches with nice round electron clouds circling about them.

Many nuclei are, in fact, sphere-shaped, but some are not: Relationships between their constituent parts deform them into bundles shaped more like a football or a discus. And physicists have predicted that in some cases, atomic nuclei could take on even more unusual shapes: pyramids, bananas, pears.

In the past, scientists have gotten glimpses of the strangely shaped nuclei, but have never been able to measure them with any precision. On Wednesday, a team of researchers described how they managed to closely study one of these exotic nucleus shapes: so-called pear-shaped nuclei, also known as "octupole deformed" nuclei, which are created under certain conditions. 

Writing in the journal Nature, the team described how, working at the ISOLDE facility at at CERN, they created short-lived isotopes out of the radioactive elements radon and radium, accelerated them in a beam to about 10% of the speed of light, and crashed them into thin metal foils. The scientists then measured radiation emitted from the nuclei to confirm that both radon and radium nuclei assumed the asymmetrical pear shape, the heavier radium more strongly than radon. 

According to two articles accompanying the study in Nature, as better equipment comes on line scientists are bound to make more measurements of exotic nuclei, including pear-shaped versions of thorium and uranium. According to University of Massachusetts physicist C.J. Lister, that will mean researchers may soon "gain a more profound understanding of how all nuclei really work" and answer broader questions in particle physics. 

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