Americium

Americium is a radioactive chemical element with the symbol Am and the atomic number 95. In chemistry, it is placed in a group of metal elements named the actinides. Americium is a transuranic element (Transuranic means after uranium as all the elements used after uranium are man-made). Americium does not exist in nature and has to be made by people. It has a silver color. Americium is made by bombarding a plutonium target with neutrons.

It was the fourth transuranic element to be discovered. It was named for the Americas, like europium was named for Europe.^[1][2]

The longest half life of any type of americium is 7370 years.^[3]

How it's made

Americium is a synthetic element. It must be made by people and is not found in nature. Most americium is made as a byproduct of nuclear reactors, and can be separated out during nuclear reprocessing.

The two most stable isotopes of americium are ²⁴¹Am and ²⁴³Am. They are made by beta decay of the same-weight plutonium isotopes, ²⁴¹Pu and ²⁴³Pu, which are made from neutron capture in thermal reactors.

Most americium is ²⁴¹Am. ²⁴¹Pu has a 14 year half-life and large fission cross section, so decaying to americium is rare in active reactors. Most ²⁴¹Am is found in spent nuclear fuel, where plutonium is more likely to decay than go through fission. ²⁴¹Am is also a byproduct of nuclear weapons production, which needs to separate ²⁴¹Pu from ²³⁹Pu to produce weapons-grade plutonium.

Uses

Americium is used in ionization-type smoke detectors. The level of radioactivity is not enough to cause cancer, and it cannot get through the smoke detector's plastic case, so it is safe to live in a place where smoke detectors with americium are used. This type of smoke detector is becoming obsolete, and is being replaced by optical smoke detectors, which have fewer false alarms and don't contain radioactive material.