Scientists have confirmed plutonium's magnetism for the first time, and the discovery may lead to significant advances in materials, energy and computing.
Plutonium was first produced in 1940 and is the most electronically complex element in the periodic table. Its magnetism was theorized for decades, but was never directly observed until now, the Oak Ridge National Laboratory reported. Plutonium's unstable nucleus allows it to undergo fission, allowing it to be a key player in nuclear fuels and even in nuclear weapons. The element also has a peculiar electronic cloud surrounding its nucleus that is equally unstable.
Plutonium's magnetism has remained mysterious because theories that have successfully explained the element's complex structural properties have predicted it should order magnetically, but experiments have found no evidence of a magnetic order. Now, after seven decades, scientists have finally discovered plutonium's "missing magnetism."
To solve the mystery, the researchers used neutron scattering.to directly measure plutonium's fluctuating magnetism. The findings revealed plutonium is not devoid of magnetism completely, but rather has magnetism that is in a constant state of flux, making it impossible to detect.
"Plutonium sort of exists between two extremes in its electronic configuration--in what we call a quantum mechanical superposition," said Marc Janoschek from Los Alamos, the paper's lead scientist "Think of the one extreme where the electrons are completely localized around the plutonium ion, which leads to a magnetic moment. But then the electrons go to the other extreme where they become delocalized and are no longer associated with the same ion anymore."
Neutron measurements made on the ARCS instrument at ORNL's Spallation Neutron Source revealed the fluctuations have different numbers of electrons in the element's outer valence shell, which could help explain abnormal changes in plutonium's volume in its different phases.
"The fluctuations in plutonium happen on a specific time scale that no other method is sensitive to," Janoschek said. "This is a big step forward, not only in terms of experiment but in theory as well. We successfully showed that dynamical mean field theory more or less predicted what we observed. It provides a natural explanation for plutonium's complex properties and in particular the large sensitivity of its volume to small changes in temperature or pressure."
The groundbreaking observations provide a microscopic explanation for why plutonium is structurally unstable, and could lead to an improved understanding of complex, functional materials that have been hard to study in the past.
The findings were published in a recent edition of the journal Science Advances.
