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Physicists solve plutonium puzzle

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Wednesday, 11 April 2001 23:52 (ET)

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

"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

 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

(Reported by UPI Science Correspondent Mike Martin in Columbia, Mo.)

Copyright 2001 by United Press International.
All rights reserved.

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