Scientists Finally Demystify Plutonium's 'Missing' Magnetism


Plutonium's magnetism has long been theorized by scientists, but they had not been able to observe this. Two national laboratories of the Department of Energy have, however, finally confirmed the existence of this magnetism.

Using neutron scattering, scientists from the Oak Ridge and Los Alamos national laboratories of DOE were able to make the first direct measurement of the distinct characteristic of plutonium's fluctuating magnetism.

For their study published in Science Advances on July 10, Marc Janoschek, from the Los Alamos National Laboratory, and colleagues said that plutonium, which was first synthesized in 1940 and is characterized by an unstable nucleus that allows it to go through fission, is not devoid of magnetism.

Although it does not lack magnetism, the chemical element, which is used in nuclear weapons and nuclear fuels, has magnetism that is in a constant state of flux, which makes it very difficult to detect.

Based on neutron measurements, the researchers found that the fluctuations have a different number of electrons in the outer valence shell of plutonium. Such fluctuation could help explain why plutonium is not magnetic. The sticking power of magnets is derived from unpaired electrons, but the number of the electrons in the outer shell of plutonium keeps changing, so unpaired electrons do not line up in a magnetic field.

"Think of the one extreme where the electrons are completely localized around the plutonium ion, which leads to a magnetic moment," Janoschek said. "But then the electrons go to the other extreme where they become delocalized and are no longer associated with the same ion anymore."

The findings also explain the abnormal changes in the volume of plutonium in its different phases.

The groundbreaking work that paved way to the discovery holds potential for applications in the fields of computer, energy and materials. The mathematical technique employed in the study, for instance, could help scientists predict the behavior of new materials. Current methods of pinning down how materials may behave were limited to conducting experiments such as hitting the materials with magnetic field or electricity as well as heating them up.

"A predictive theory of materials is a big deal because we eventually will be able to simulate and predict properties of materials on a computer," said Rutgers physics professor Gabriel Kotliar. "For radioactive materials like plutonium, that's a lot cheaper than doing an actual experiment."

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