New Picture of Atomic Nucleus Emerges

March 5, 2012

by Jared Sagoff

When most of us think of an atom, we think of tiny electrons whizzing around a stationary, dense nucleus composed of protons and neutrons, collectively known as nucleons. A collaboration between the U.S. Department of Energy’s Argonne and Thomas Jefferson National Laboratories has demonstrated just how different reality is from our simple picture, showing that a quarter of the nucleons in a dense nucleus exceed 25 percent of the speed of light, turning the picture of a static nucleus on its head.

“We normally picture a nucleus as this fixed arrangement of particles, when in reality there’s a lot going on at the subatomic level that we just can’t see with a microscope,” said Argonne physicist John Arrington.
Arrington and his colleagues used one of the Jefferson Lab’s large magnetic spectrometers to look at the behavior of nucleons in some light atoms – deuterium, helium, beryllium and carbon. Physicists had long believed that “short-range correlations” -- the interactions within nuclei that produced high-momentum nucleons – would largely reflect the density of the atom’s nucleus, as they did in heavier nuclei.

This hypothesis largely held true, except in the case of beryllium.

Visit Argonne National Laboratory online for full announcement.