Americium
Element 95 · Actinide
Americium is a silvery-white synthetic metal that is malleable and glows faintly in the dark. It is produced in nuclear reactors and is a strong alpha emitter. Its most familiar application is the tiny americium-241 source inside ionization-type smoke detectors, where alpha particles ionize air in a sensing chamber. It also serves as a portable neutron source when mixed with beryllium. All americium isotopes are radioactive, decaying mainly by alpha emission.
Key facts
| Atomic number | 95 |
|---|---|
| Atomic weight | [243] |
| Category | Actinide |
| Group / Period | — / 7 |
| Block | f |
| Electron configuration | [Rn] 5f7 7s2 |
| Common oxidation states | +3, +4, +5, +6 |
| State at STP | Solid |
| Electronegativity | 1.13 |
| Density | 12 g/cm3 |
| Melting point | 1176 °C |
| Boiling point | 2607 °C |
Occurrence
Americium is entirely synthetic, produced in kilogram quantities per year by neutron irradiation of plutonium in nuclear reactors. It does not occur naturally.
Applications
Americium-241 in ionization-type smoke detectors
Neutron sources for industrial gauges (with beryllium)
Research target for synthesizing heavier elements
Common compounds
- Americium dioxide (AmO2)
- Americium(III) oxide (Am2O3)
- Americium(III) fluoride (AmF3)
Americium was discovered in 1944 by Glenn Seaborg's team and named after the Americas, matching europium which was named after Europe.
Data source: IUPAC standard atomic weights 2021