Physicists using the European Synchrotron Radiation Facility have created a new compound of plutonium (Pu) with an unexpected, pentavalent oxidation state — Pu (V). The new compound is solid and stable, and may represent a transient phase in radioactive waste repositories. A plutonium dioxide nanoparticle. Image credit: Kristina Kvashnina. One of the most fundamental properties of the chemical behavior of Pu is the variety of its oxidation states...