The nuclei of radioactive elements are unstable, meaning they are transformed into other elements, typically by emitting particles (and sometimes by absorbing particles). Natural uranium consists of three isotopes: uranium-238, uranium-235, and uranium-234. Uranium is the principal fuel for nuclear reactors and the main raw material for nuclear weapons.

In 1938, German physicists Otto Hahn and Fritz Strassmann showed that uranium could be split into parts to yield energy. Some of the terms used in this factsheet are defined in IEER’s on-line glossary.įirst discovered in the 18th century, uranium is an element found everywhere on Earth, but mainly in trace quantities.