After 50 years of searching, physicists have spotted the fingerprint of radioactive plutonium, revealing the secrets of this complex molecule behind nuclear weapons.

The researchers found the "plutonium signal" using nuclear magnetic resonance spectroscopy, which is often used to peer into the electronic structure of atoms and molecules.

Their findings, detailed in the May 18 issue of the journal Science, could help scientists and others figure out the relative amounts of different types of plutonium (and its many compounds) in nuclear reactors, for instance.