Magazine article Science News

Explosive Expansion of Atomic Nuclei

Magazine article Science News

Explosive Expansion of Atomic Nuclei

Article excerpt

In its normal state, an atomic nucleus behaves much like a drop of water. Its neutrons and protons hang together as if they were components of a liquid.

Now, researchers have confirmed experimentally that heating up an atomic nucleus to temperatures far hotter than the sun's interior causes the nucleus to expand by nearly 50 percent in diameter. Only then does the nucleus disintegrate into many pieces.

"This is the first direct evidence for the expansion of nuclear matter," says nuclear chemist Victor E. Viola of Indiana University at Bloomington.

Knowledge of how nuclei expand and contract under different conditions furnishes insights into such astrophysical processes as the collapse of ordinary stellar material into a neutron star--a giant nucleus, in effect, with a mass comparable to that of the sun but a diameter of only 10 kilometers.

Viola reported these findings last week at an American Chemical Society meeting in Anaheim, Calif. The results also will be published in an upcoming issue of Physical Review Letters.

Theorists have long found it useful to model an atomic nucleus as a drop of liquid. On this basis, they have suggested that a nucleus could, under certain circumstances, change from a liquid to a more loosely bound gaseous state. Some theorists have also predicted that intense heating could cause a nucleus to expand considerably.

"The model that I have been developing and working with suggests that the expansion happens first, and then at low density the nucleus tends to break apart," says physicist William A. Friedman of the University of Wisconsin--Madison, who consulted with Viola's team.

As a complement to the theoretical work, experimentalists have typically studied the characteristics of nuclear matter by smashing together large, heavy nuclei and sifting through the debris for clues. …

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