There is almost certainly a speck of americium in your home right now. Less than a microgram — but it saves lives every day. This radioactive metal hides inside the smoke detector on your ceiling. It ionizes the air, and when smoke enters the chamber — the alarm goes off.
Americium does not exist in nature. Scientists created it in 1944 by bombarding plutonium with neutrons. They named it after America — mirroring europium, named after Europe. A silvery-white metal, soft and heavy. Density: 13.7 g/cm³, almost like lead. The half-life of Am-241 is 432 years. Enough for a detector to work for decades.
Americium is a synthetic element from the actinide family. Its atomic number is 95. In pure form, it is a silvery-white metal that slowly tarnishes in air. It emits alpha particles — heavy but with low penetrating power. A sheet of paper stops them.
Its main use is ionization smoke detectors. Am-241 is also used in industry to measure the thickness of sheet metal and glass. Scientists are investigating Am-241 as a potential power source for spacecraft — replacing scarce plutonium-238.
Americium is a radioactive alpha emitter. Alpha particles cannot penetrate skin or even a sheet of paper. But if inhaled or swallowed, they cause serious internal damage. In a smoke detector, americium is safe — it is hermetically sealed in a metal capsule. The key rule: never disassemble a detector, and always dispose of old units through specialized recycling programs.
Most household smoke detectors contain Am-241 — just 0.3 micrograms. This tiny speck ionizes the air inside the chamber and detects smoke within seconds.
Americium was named after America. Europium was named after Europe. In the periodic table, they sit directly above each other: europium among the lanthanides, americium among the actinides.
Glenn Seaborg announced americium on a children's radio show in 1945 — before the official scientific publication. A boy in the audience asked about new elements.
The half-life of Am-241 is 432 years. A smoke detector with americium will work for decades until the electronics fail — not the radioactive source.
The European Space Agency is studying americium as fuel for space batteries. Am-241 is cheaper and more available than plutonium-238.
Factories use americium to measure the thickness of glass and metal sheets. An alpha beam passes through the material, and sensors determine thickness down to microns.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
241Am☢ | 241.056829 | synthetic | 432.2 years | α |
243Am☢ | 243.061373 | synthetic | 7370 years | α |
Neutron bombardment of plutonium