Magazine article Science News

Deformed Nuclei Spit out Protons

Magazine article Science News

Deformed Nuclei Spit out Protons

Article excerpt

A rare type of radioactive decay can signal the shape of an atom's nucleus.

By determining the rate at which the unstable nuclei of two elements emit protons, researchers have for the first time obtained experimental evidence that these particular nuclei look more like flattened globes than true spheres.

"We haven't actually measured the deformation, but our results show these nuclei to be highly deformed," says Cary N. Davids of Argonne (Ill.) National Laboratory. Davids and an international team of researchers describe their findings in the March 2 Physical Review Letters.

"It's a new example of proton radioactivity and, more than that, an excellent example of the ability to deduce something about the shape of a nucleus from the properties of the decay," says Richard F. Casten of Yale University.

Atomic nuclei are made up of protons and neutrons. Normally, neutrons help prevent the electrostatic repulsion between the positively charged protons from splitting the nucleus apart.

Many nuclei are unstable, however, because they contain too many protons for the number of neutrons present. Such proton-rich nuclei sometimes become more stable by spontaneously ejecting a proton.

In proton radioactivity, a proton deep inside the nucleus penetrates an outer surface shell of protons. To get through the barrier, it takes advantage of a quantum effect known as tunneling.

During the last few years, Davids and his colleagues have been smashing stable nuclei together to create unstable, proton-rich nuclei and looking for evidence of proton radioactivity among these short-lived isotopes. …

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