Americium, symbol Am, is an artificially created, malleable, radioactive metallic element somewhat similar to lead. The atomic number of americium is 95 and its atomic weight is 243. The element is one of the transuranium elements in the actinide series of the periodic table.
Americium was the fourth transuranic element to be synthesized. It was discovered in 1944 and 1945 by the American physicist Glenn Seaborg and his associates at the University of Chicago. They synthesized the americium isotope of mass number 241 by bombarding plutonium-239 with neutrons. Americium isotopes with mass numbers 237 to 247 have been formed; they are all radioactive, with half-lives of from 0.9 minute (americium-232) to about 7,400 years (americium-243) (see Radioactivity). Americium-243 is used as target material in nuclear reactors or particle accelerators for the production of even heavier synthetic elements. Americium melts at 1180°C (2156°F), boils at 2010°C (3650°F), and has a specific gravity of 13.7.
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