Americium

Americium was first intentionally produced and identified in late 1944 at the University of California, Berkeley as part of the Manhattan Project by Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso. It was chemically identified at the Metallurgical Laboratory of the University of Chicago. Although it is the third element in the transuranic series, it was the fourth transuranic element to be discovered. Its discovery was kept secret and wasn't released to the public until November 1945.

Americium is a man-made radioactive chemical element. It is a transuranic (meaning beyond uranium) member of the actinide series. In the periodic table, it is located under its twin lanthanide element, europium. Matching its twin, it was named americium by analogy and because it was first produced in the United States.

Americium is a highly radioactive, silvery-white, man-made element. It slowly tarnishes in dry air at room temperature. Americium is less dense than both curium and plutonium; but has a higher density than europium—mostly because of its higher atomic mass. Americium is relatively soft and easily deformable. It readily reacts with oxygen and dissolves in aqueous acids. Its melting point is 1176°C, its boiling point is 2011°C, and its density is 12 g/cm³.

Americium can be produced in kilogram quantities and has few practical uses. Americium is commonly used in smoke alarms, keeping us firesafe.

Americium is used in smoke detectors for its alpha particles. Alpha particles ionize air molecules creating negatively and positively charged particles. There is a constant flow of the charged particles inside the smoke detector, and when broken by smoke, the alarm is triggered.

Americium can also be used as a portable source of gamma rays for medical and industrial uses, such as spectroscopy, radiography, and the creation of flat glass. It has the potential to be used in spacecraft batteries in the future, but that use is hindered by the scarcity and high price of this element ($1500/gram).

Americium reacts with oxygen to form the dioxide AmO₂. It reacts with halogen elements to form compounds such as tetrafluoride (AmF₄). It reacts with hydrogen to form the hydride AmH₂. It has four oxidation states in acidic aqueous solutions: Am³⁺ (pink), Am⁴⁺ (rose colored and very unstable), AmO²⁺ (yellow), and AmO₂²⁺ (light tan).

There are at least 19 radioactive isotopes. The longest-lived and most common isotopes of americium, americium-241 and -243, have half-lives of 432.2 and 7,370 years, respectively. Because of the length of these half-lives, any americium that was present during the formation of the earth should have decayed by now. Americium-241 produces about three times as much alpha radiation as radium.

Americium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors. It also is concentrated in areas that were used for atmospheric nuclear tests and nuclear accident sites, such as Chernobyl.

Americium has also been theoretically detected in stars. It may occur naturally in extremely small trace amounts in uranium minerals because of nuclear reactions.