- Americium (Am) is a silvery-white, radioactive metal with atomic number 95, belonging to the actinide series.
- Its electron configuration is [Rn] 5f⁷ 7s², and it exhibits oxidation states from +2 to +7, though +3 is the most stable and dominant in compounds. The atomic structure contains ninety-five protons, most commonly one hundred and forty-six neutrons in americium-241 (²⁴¹Am), and ninety-five electrons arranged in seven shells.
- Americium does not occur naturally in significant amounts; it is produced artificially in nuclear reactors as a byproduct of plutonium irradiation. The two most important isotopes are americium-241 (²⁴¹Am), with a half-life of 432.2 years, used in commercial devices, and americium-243 (²⁴³Am), with a half-life of 7,370 years, used mainly in research.
- Americium was first identified in 1944 by Glenn T. Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso at the University of California, Berkeley, during experiments with the Manhattan Project. It was discovered by bombarding plutonium-239 (²³⁹Pu) with neutrons to form plutonium-241 (²⁴¹Pu), which beta decayed into americium-241. The name “americium” follows the naming pattern of its lighter homolog europium (a lanthanide), while also reflecting its discovery in the Americas.
- The most common application of americium is in americium-241-based alpha particle sources, widely used in ionization-type smoke detectors, where it ionizes air to detect smoke particles. It is also used in portable gamma-ray sources for industrial radiography, in neutron sources (when combined with beryllium), and in scientific research.
- Chemically, americium resembles other actinides and rare earth elements. In its metallic form, americium tarnishes slowly in air, forming a thin oxide layer. Americium(III) oxide (Am₂O₃) is its most stable compound, while higher oxidation states such as Am(VI) and Am(VII) occur in strong oxidizing environments. Americium forms halides (AmF₃, AmCl₃, AmBr₃) and complex ions, such as americyl (AmO₂⁺ and AmO₂²⁺), similar to uranyl and neptunyl species.
- Biologically, americium has no known essential role in living organisms and is highly radiotoxic due to its alpha emissions. Inhaled americium is especially dangerous, as it tends to deposit in the lungs, bones, and liver, where it remains for decades, increasing cancer risk.
- Environmentally, americium can be released from nuclear weapons testing, nuclear accidents, and improper handling of nuclear waste. While its alpha radiation poses minimal risk outside the body, ingestion or inhalation of americium particles is hazardous. The long half-life of ²⁴³Am and ²⁴¹Am makes them important in long-term nuclear waste management strategies.
