Americium-241

Americium-241 (²⁴¹
Am
, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of 432.2 years. ²⁴¹
Am
is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It is commonly found in ionization type smoke detectors and is a potential fuel for long-lifetime radioisotope thermoelectric generators (RTGs). Its common parent nuclides are β⁻ from ²⁴¹
Pu
, EC from ²⁴¹
Cm
, and α from ²⁴⁵
Bk
. ²⁴¹
Am
is not fissile, but is fissionable, and the critical mass of a bare sphere is 57.6–75.6 kilograms (127.0–166.7 lb) and a sphere diameter of 19–21 centimetres (7.5–8.3 in). Americium-241 has a specific activity of 3.43 Ci/g (126.91 GBq/g). It is commonly found in the form of americium-241 dioxide (²⁴¹
Am
O
₂). This isotope also has one meta state, ^241m
Am
, with an excitation energy of 2.2 MeV (0.35 pJ) and a half-life of 1.23 μs. The presence of americium-241 in plutonium is determined by the original concentration of plutonium-241 and the sample age. Because of the low penetration of alpha radiation, americium-241 only poses a health risk when ingested or inhaled. Older samples of plutonium containing ²⁴¹
Pu
contain a buildup of ²⁴¹
Am
. A chemical removal of americium-241 from reworked plutonium (e.g., during reworking of plutonium pits) may be required in some cases.