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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

Electron Shell Configuration:


2s2   2p6

3s2   3p6   3d10

4s2   4p6   4d10   4f14

5s2   5p6   5d10   5f7

6s2   6p6