An Overview about the Chemical Element Americium


Symbol: Am

Atomic Number: 95

Atomic Mass: 243.0 amu (atomic mass units)

Melting Point: 994.0 C (1267.15 K, 1821.2 F)

Boiling Point: 2607.0 C (2880.15 K, 4724.6 F)

Number of Protons/Electrons: 95

Number of Neutrons: 148

Classification: Rare Earth Metal (Man Made)

Crystal Structure: Hexagonal

Density @ 293 K: 13.6 grams per cubic centimeter

Color: Silver/white

The transuranium element americium was first produced in 1944 by Glenn T. Seaborg, Ralph A. James, Leon O. Morgan and Albert Ghiorso. This team of American scientists were working at the University of Chicago’s Metallurgy Laboratory (this facility is now called the Argonne National Laboratory). The element is named after the Americas.

Americium was the fourth of the transuranium elements to be made. It was produced by a series of neutron bombardments. Plutonium-239 was bombarded by neutrons to form plutonium-240. When this isotope was itself subjected to neutron bombardment plutonium-241 was formed. The plutonium-241 decayed by beta decay to form americium-241 which has a half life of 432.2 years and decays by alpha decay.

A number of other isotopes of americium have now been made. These isotopes have mass numbers ranging from 231 to 249. The isotope americium 243 has the longest half life at 7370 years. Americium-243 will decay by alpha decay to form neptunium-239 it can also decay by spontaneous fission. The shortest half-life at 73 microseconds belongs to the isotope americium-246m2 which decays by spontaneous fission.

Americium is a rare earth metal belonging to the actinide or actinoid series of the periodic table. It will tarnish in dry air at room temperature. The metal seems to be more malleable than either uranium or neptunium. Americium is an extremely radioactive element. Americium-241 has three times the alpha activity of the element radium. The element is also a very powerful gamma emitter. Because of the inherent dangers of radioactivity all work with the element must be carried out with caution and with the appropriate safe guards in place.

The element has never been found in nature but the nuclear industry has been able to produce kilogram amounts of americium. Americium has a few industrial applications. The isotope used for these applications is americium-241 as fairly pure samples of this isotope can be produced

* It is used as a gamma emitter in portable gamma radiography equipment.

* Americium provides an ionization source in some smoke detectors.

* It can be use to make a radioactive glass thickness gauge.

Los Alamos National Laboratories Chemistry Division