In a new research paper appearing in Nature, a group of scientists have discovered that the spin dependence of the nuclear force between nucleons disappears as the nucleons come close to one another within a nucleus.

The new paper is authored by a large host of scientists using the Jefferson Lan’s Continuous Electron Beam Accelerator Facility’s Large Acceptance Spectrometer detector in Newport News. Among the authors is David Jenkins, professor emeritus in residence with the Department of Physics.

“The nucleus of an atom is a system of nucleons that interact with each other, similar to billiard balls in a box, colliding with one another as they move about the box,” Jenkins said. “When a ball tries to escape the box, the attractive nuclear force pulls it back. Further study revealed that the nucleons have spin, making them look like spinning tops as they move within the nucleus. In studying the nature of the force between two nucleons, scientists found that the force can depend on their relative spin.”

Using an electron beam on the detector, electrons were scattered on carbon, aluminum, iron, and lead to look for interactions with the ejection of one or two nucleons. The experiment, Jenkins said, found a change in the nature of the nuclear force as the nucleon’s separation distance decreases.  

The experiment’s impact is far-reaching.

“The results will contribute to our knowledge of neutron stars,” Jenkins added. “Neutron stars are formed by a supernova explosion of a massive star, followed by a gravitational collapse to form a system with the density of an atomic nucleus. Knowing how the constituents of the neutron star interact, the paper will contribute to our understanding of the formation and evolution of the universe.”