Actinium can be found naturally in traces in uranium ore as Ac, an α and β emitter with half-life 21.773 years. Uranium ore contains about 0.2 mg of actinium per ton of uranium. It is more commonly made in milligram amounts by neutron irradiation of Ra in a nuclear reactor. Natural actinium almost exclusively consists of one isotope, Ac, with only minute traces of other shorter-lived isotopes (Ac and Ac) occurring in other decay chains.