Americium: Symbol: Am. A man-made metallic element whose isotopes Am-237 through Am-246 are all radioactive. Americium must be handled with great care to avoid personal contamination. Trace quantities of americium are widely used in smoke detectors. It is also used in bone mineral analysis and as a radiation source for radiotherapy.

Americium was discovered in 1944 at the wartime metallurgical laboratory at the University of Chicago as the result of successive neutron capture reactions by plutonium isotopes in a nuclear reactor.