DENSITY : 13.6 g/cm 3
MOST COMMON IONS : Am 3+ , AmO 2 + , AmO 2 2+

Americium is a synthetic radioelement , first produced in 1944 via the bombardment of plutonium with neutrons by Glenn Seaborg and coworkers as part of the Manhattan Project . The first isolation of a compound of americium, Am(OH) 3 , was achieved by B. B. Cunningham in the fall of 1945. Many radioactive isotopes of americium have been isolated and identified, having mass numbers that range from 237 through 247. The longest-lived americium isotope has mass number 243 and a half-life of 7,380 years. The ground state (outer orbital) electronic configuration for a neutral atom is 5 f 2 6 d 7 s 2 . The outer d and s electrons are lost to form americium in its most stable oxidation state, +3, in solutions and compounds. Americium is the first of the actinide elements to appear in the characteristic stable trivalent state in solution. Americium, in the V and VI oxidation states, forms the linear oxo cations AmO 2 + and AmO 2 2+ —chemical behavior that is characteristic of actinide elements.

Metallic americium has a face-centered cubic structure at its melting point and a double hexagonal closed-packed structure at temperatures below its melting point. The isotope americium-241 emits α -particles and γ -rays in its radioactive decay , and is a source of γ -radiation, used to measure the thickness of metals , coatings, degree of soil compaction, sediment concentration, and so on. The same isotope, mixed with beryllium, is used as a neutron source in oilwell logging and other applications. Americium-241 has been used in smoke detectors; its α -emissions ionize the surrounding air and the resulting ions provoke electronic signals when they come into contact with electrodes in the detector.

SEE ALSO Actinium ; Berkelium ; Einsteinium ; Fermium ; Lawrencium ; Mendelevium ; Neptunium ; Nobelium ; Plutonium ; Protactinium ; Rutherfordium ; Seaborg, Glenn Theodore ; Uranium .

Gregory R. Choppin


Choppin, Gregory R.; Liljenzin, Jan-Olov; and Rydberg, Jan (2001). Radiochemistry and Nuclear Chemistry , 3rd edition. Woburn, MA: Butterworth-Heinemann.

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements beyond Uranium. New York: Wiley-Interscience.

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