Plutonium is one of the most complex elements in the periodic table. First synthesized and isolated in 1940 by scientists at the University of California, Berkeley, plutonium has been studied closely for more than eight decades. It's most often associated with its role in nuclear security, but it's also vital to nuclear power, where it is produced in reactors and can be recycled as fuel. Despite plutonium's importance, some of its most fundamental behaviors remain a mystery.