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Physicists solve plutonium puzzle
|Wednesday, 11 April 2001 23:52
Physicists solve plutonium puzzle NEW BRUNSWICK, N.J., April 11 (UPI) -- Physicists at Rutgers University claim they have devised the first reliable method to predict the way plutonium will behave in long-term nuclear waste storage. In a paper appearing in the April 12 issue of the journal Nature, Sergej Savrasov, Gabriel Kotliar, and Elihu Abrahams present a computerized method that simulates the configuration of plutonium atoms at various temperatures and pressures. The method places plutonium atoms in different positions on a three-dimensional lattice array under varying conditions. Using this simulation, the researchers say they can predict under what conditions plutonium atoms will assume their most stable spatial configurations. "We devised this computer method to model plutonium because the Coulomb interactions between the electrons are so strong, other methods won't work," said Sergej Savrasov, one of the paper's authors. "The original theory underlying our method was developed about ten years ago by Gabriel Kotliar," Savrasov told United Press International from his office at the Rutgers University Center for Materials Theory. Plutonium is highly toxic and rarely occurs in nature, Savrasov explained, making direct observation of the element all the more difficult. He told UPI his team is also interested in applying their computer simulation to other materials that elude traditional study. "In the past, we've seen computer simulations like this one applied to hypothetical materials," Savrasov explained. "We now hope to apply this method to realistic materials -- not only plutonium, but also certain types of high-temperature superconductors." Savrasov sees real-world applications for his team's technique in the design and storage of nuclear waste. "We are trying to tell a person who is going to store plutonium waste under what conditions it can best be kept stable over the very long term," Savrasov said. Jim Amonette, a senior research scientist at the DOE department of environmental dynamics and simulation, told UPI such a technique may indeed work. "We do a lot of modeling here and I do know enough to say that such a model could be very useful," Amonette said from his Hanford, Washington office. However, Dhan Rai, a plutonium specialist with Battelle Pacific Northwest Laboratories at Washington's Hanford nuclear site, said problems with the storage containers themselves often overshadow problems with plutonium. "We have found instances where the metal containers are unstable," Rai told UPI. Plutonium is stored in a dry state in such containers which, Rai explained, are susceptible to moisture, oxidation, heat, and pressure. Andrew Millis, a Rutgers physics professor who is not involved in the plutonium simulation, told UPI he sees much farther reaching applications for the technique. "Before Kotliar's method, we were not able to accurately describe the behavior of many-body systems at temperatures above absolute zero or when atoms in excited states were involved," Millis told UPI. "Kotliar's method is also superior when describing strong electron-electron interactions between atoms." Millis termed Kotliar and his team's simulation a brilliant supplement to the so-called "density functional method," which was developed in 1964 and won the Nobel Prize for its creators in 1999. "The density functional method worked well when you wanted to describe atoms in ground, or lowest energy states, or at absolute zero temperature," Millis said. "It was not a good method for nonzero temperatures or atoms in higher, excited energy states." Millis believes Kotliar and his team have reached the culmination of twenty years research in solid state physics with this new computer simulation, which has also allowed researchers to calculate the transition temperature of iron for the first time. "The transition temperature of iron is the point at which it stops being magnetic," Millis explained. "I want to emphasize that modeling plutonium is only the beginning for this method. It is a major breakthrough on many fronts." (Reported by UPI Science Correspondent Mike Martin in Columbia, Mo.) -- Copyright 2001 by United Press International. All rights reserved. --
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