americium

Americium is a synthetic radioactive chemical element with the symbol Am and atomic number 95. It belongs to the actinide series in the periodic table and is produced primarily in nuclear reactors as a decay product of certain plutonium isotopes.

Americium was discovered in 1944 at the University of California, Berkeley, by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso during the Manhattan Project. It was identified in irradiated plutonium oxide, and the element was named americium to reflect its American discovery.

The most common isotope is americium-241, produced in reactors from plutonium isotopes and possessing a half-life of 432.2 years. Am-241 decays by alpha emission to neptunium-237 and emits low-energy gamma rays, notably a 59.5 keV photon. Although primarily an alpha emitter, its gamma component allows detection and measurement in some applications.

Americium is not found naturally in significant quantities and is manufactured in reactors from plutonium (and to a lesser extent uranium) via neutron capture and beta decay. It is typically obtained from irradiated fuel or prepared as sealed sources for specialized uses.

Applications include its widespread use in household smoke detectors, where a small sealed Am-241 source ionizes air to enable detection of smoke. It is also employed in some industrial gauges and moisture-density measurement devices. Due to its radioactivity, handling and disposal are regulated, with sealed sources designed to minimize exposure and prevent environmental release.