The Element Americium
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Atomic Number: 95
Atomic Weight: 243
Melting Point: 1449 K (1176°C or 2149°F)
Boiling Point: 2284 K (2011°C or 3652°F)
Density: 13.69 grams per cubic centimeter
Phase at Room Temperature: Solid
Element Classification: Metal
Period Number: 7 Group Number: none Group Name: Actinide
Radioactive and Artificially Produced
What's in a name? Named for the Americas.
Say what? Americium is pronounced as am-er-ISH-ee-em.
History and Uses:
Americium was discovered in 1944 by the American scientists Glenn T. Seaborg, Ralph A. James, Leon O. Morgan and Albert Ghiorso. They produced americium by bombarding plutonium-239, an isotope of plutonium, with high energy neutrons. This formed plutonium-240, which was itself bombarded with neutrons. The plutonium-240 changed into plutonium-241, which then decayed into americium-241 through beta decay. This work was carried out at the University of Chicago's Metallurgical Laboratory, now known as Argonne National Laboratory.
Americium's most stable isotope, americium-243, has a half-life of about 7,370 years. It decays into neptunium-239 through alpha decay.
Americium can be produced in kilogram quantities and has a few practical uses. It is used in smoke detectors and can be used as a portable source of gamma rays. Americium-241, with a half-life of 432.2 years, is used in these products because it is easier to produce relatively pure samples of this isotope.
Estimated Crustal Abundance: Not Applicable
Estimated Oceanic Abundance: Not Applicable
Number of Stable Isotopes: 0 (View all isotope data)
Ionization Energy: 5.993 eV
Oxidation States: +6, +5, +4, +3
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10 5f7