An Etymological Dictionary of Astronomy and Astrophysics

An artificially produced → radioactive→ chemical element; symbol Am. → Atomic number 95; → atomic weight of most stable → isotope 243; → melting point about 1,175°C; → boiling point about 2,600°C; → specific gravity 13.67 at 20°C; → valence +2, +3, +4, +5, or +6. Its most stable isotope, ²⁴³Am, has → half-life
of 7.4 x 10³ years.

See also: From America, where it was first synthesized in 1944 by Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, and Albert Ghiorso, who bombarded plutonium-239 with neutrons to form plutonium-241, which decays to form americium-241.