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Titan Helps ­npuzzle Decades-Old Plutonium Perplexities

Comparison of the predicted S(q,?) for d-Pu (right) with the experimental observations (left).

Rutgers University researchers have calculated the electronic and magnetic structure of plutonium.

Credit: Oak Ridge National Laboratory

Rutgers University researchers used an allocation by the U.S. Department of Energy's Office of Advanced Scientific Computing Research Leadership Computing Challenge and nearly 10 million Titan supercomputer core hours to calculate the electronic and magnetic structure of plutonium.

The researchers relied on a combination of density functional theory (DFT) calculations and the dynamical mean field theory (DMFT) technique.

The research found plutonium is in a constant state of flux, at small but finite energies, which is why it has been nearly impossible to detect for more than 70 years.

"DFT+DMFT correctly predicted the energy needed to excite the spin excitations within numerical and experimental errors," an accomplishment that could have only been achieved on a machine as massively parallel as Titan, according to Rutgers professor Gabriel Kotliar.

Meanwhile, Los Alamos National Laboratory (LANL) researchers used neutron-scattering experiments to obtain physical confirmation that plutonium's dynamical magnetism was not just a theory. The researchers determined the fluctuations carry varying numbers of electrons in plutonium's outer valence shell, which explained why abnormal changes occur in the differing phases of plutonium's volume. The results provide "a natural explanation for plutonium's complex properties and in particular the large sensitivity of its volume to small changes in temperature or pressure," says LANL researcher Marc Janoschek.

From Oak Ridge National Laboratory
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