Rutgers Physicists Tackle Plutonium Complexities

In a paper appearing in the April 11 issue of the journal Nature, Rutgers' Sergej Y. Savrasov, a postdoctoral associate; Gabriel Kotliar, professor of physics; and Elihu Abrahams, director of the Center for Materials Theory, present a novel electronic structure method for predicting stability changes in plutonium, potentially a landmark achievement in solid-state physics.

Plutonium is regarded even by scientists as a complex and mysterious element, rarely occurring in nature, and made artificially for the first time in 1940. "Just as water has phases – liquid, solid and gaseous – so does plutonium," explained Kotliar. "In plutonium, there are many more solid phases, ranging from a dense and unstable alpha phase to a much more extended and stable delta phase. The potential decomposition into the unstable phase over time is a matter of concern in old, stored nuclear warheads, where this could ultimately result in changes in the mass that could lead to a chain reaction.

"While the search for answers about plutonium phases generally has been through experimental methods, we employed analytical and computer calculations to predict changes in the structure of the solid states of plutonium," said Kotliar. "We felt a strong need for theoretical methods that are accurate. This element is far too toxic for extensive experimental procedures in the laboratory, and the use of theoretical methods is mandatory if we are to deal with problems over long time scales. Experimental methods do not work for predicting changes 100 years into the future."

In developing its new method, the team employed Rutgers' High-Performance Computing Cluster, a computational grid comprising more than 80 computer processors configured as a distributed resource, and a Department of Energy supercomputer. The researchers can now predict volume and stability changes in plutonium while gaining insights into where and when the transition between the alpha and delta phases occurs and under what conditions.

"We are dealing with an extremely delicate balance between the two phases, and which one wins and when this happens is information that is necessary to assure the safe storage of this important material," added Kotliar.