Americium Facts: Element 95 or Am

Americium is a silver-colored, radioactive metallic element.
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Americium is a radioactive metallic element with atomic number 95 and element symbol Am. It's the only synthetic element encountered in everyday life, in minute quantities in ionization-type smoke detectors. Here is a collection of interesting americium facts and data.

Americium Facts

Americium was first synthesized and identified in 1944 by Glenn T. Seaborg, Ralph James, L Morgan, and Albert Ghiorso at the University of California, Berkeley as part of the Manhattan Project. The element was produced using a 60-inch cyclotron, although it's likely earlier experiments had also produced the element. Although element 95 was discovered by synthesizing it, americium occurs naturally as a trace element in uranium-containing minerals. In the distant past, the element occurred naturally from nuclear reactions as recently as a billion years ago. All of this americium has already decayed into daughter isotopes.

The element name americium is for America. Americium is located directly below the lanthanide element europium, which is named for Europe.

Americium is a shiny silver radioactive metal. All isotopes of this element are radioactive. The isotope with the longest half-life is americium-243, which has a half-life of 7370 years. The most common isotopes are americium-241, with a half-life of 432.7 years, and americium-243. Americium-242 is also known, with a half-life of 141 years. In total, 19 isotopes and 8 nuclear isomers have been characterized. The isotopes variously undergo alpha, beta, and gamma decay.

The primary uses of americium are in smoke detectors and for scientific research. It's possible the radioactive element may be used for spacecraft batteries. Americium-241 pressed with beryllium is a good neutron source. Like many radioactive elements, americium is useful for producing other elements. Element 95 and its compounds are useful portable alpha and gamma sources.

Nuclear power plants naturally produce americium as part of the decay sequence from the neutron bombardment of plutonium. A few grams of the element is produced using this method each year.

The physical and chemical properties of americium are similar to those of plutonium (the element to its left on the periodic table) and europium (the element above it on the periodic table). Fresh americium is a shiny silver-white lustrous metal, but it slowly tarnishes in air. The metal is soft and easily deformed with a lower bulk modulus than the actinides preceding it on the table. Its melting point is higher than that of plutonium and europium, but lower than that of curium. Americium is less dense than plutonium, yet denser than europium.

Americium is paramagnetic over a wide temperature range, from extremely cold temperatures to above room temperature.

The most common oxidation state of element 95 is +3, but it can range anywhere from +2 to +8. The range of oxidation states is the widest for any actinide element. The ions are colored in aqueous solution. The +3 state is colorless to reddish yellow, +4 state is reddish yellow, with brown and green colors for other states. Each oxidation state has a distinctive absorption spectrum.

The crystal structure of americium depends on temperature and pressure. Under normal conditions, the metal is seen in a stable alpha form that has hexagonal crystal symmetry. When the metal is compressed, it changes to the beta form, which has face-centered cubic symmetry. Increasing the pressure even more (23 GPa) transforms americium into its gamma form, which is orthorhombic. A monoclinic crystal phase has also been observed, but it's unclear exactly what conditions cause it. Like other actinides, americium self-damages its crystal lattice from alpha decay. This is especially noticeable at low temperatures.

The metal dissolves in acids and reacts with oxygen.

Americium may be used together with phosphorescent zinc sulfide to make a homemade spinthariscope, which is a sort of radiation detector that predates the Geiger counter. The radioactive decay of americium provides energy to the phosphor, causing it to emit light.

There is no known biological role of americium in living organisms. It's generally considered toxic because of its radioactivity.

Americium Atomic Data

  • Element Name: Americium
  • Element Symbol: Am
  • Atomic Number: 95
  • Atomic Weight: (243)
  • Element Group: f-block element, actinide (transuranic series)
  • Element Period: period 7
  • Electron Configuration: [Rn] 5f7 7s2 (2, 8, 18, 32, 25, 8, 2)
  • Appearance: Silver metallic solid.
  • Melting Point: 1449 K ​(1176 C, ​2149 F)
  • Boiling Point: 2880 K ​(2607 C, ​4725 F) predicted
  • Density: 12 g/cm3
  • Atomic Radius: 2.44 Anstroms
  • Oxidation States: 6, 5, 4, 3
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Your Citation
Helmenstine, Anne Marie, Ph.D. "Americium Facts: Element 95 or Am." ThoughtCo, Aug. 1, 2021, Helmenstine, Anne Marie, Ph.D. (2021, August 1). Americium Facts: Element 95 or Am. Retrieved from Helmenstine, Anne Marie, Ph.D. "Americium Facts: Element 95 or Am." ThoughtCo. (accessed March 20, 2023).