Americium isotope Am241 was identified by a group of researchers at the University of Chicago in 1944 and was the fourth trans-uranium element to be discovered, via successive neutron capture reactions by plutonium isotopes in a nuclear reactor.
Americium metal can be prepared by reducing the trifluoride with barium vapour at approximately 1000-1200°C (1832-2032°F) or the dioxide by lanthanum metal. Prepared in this manner its luster is whiter and more silvery than plutonium or neptunium. It tarnishes slowly in dry air at room temperature and is thought to be more malleable than uranium or neptunium.
It is believed to exist in two forms, an alpha form, which has a double hexagonal close-packed structure, and a loss-packed cubic beta form. The alpha activity from Am241 is three times that of radium and must be handled with great care to avoid human contamination.