Americium-242

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Transmutation flow between ²³⁸Pu and ²⁴⁴Cm in LWR.^[1]
Fission percentage is 100 minus shown percentages.
Total rate of transmutation varies greatly by nuclide.
²⁴⁵Cm–²⁴⁸Cm are long-lived with negligible decay.

Americium-242m is a radioactive isotope of Americium with 95 protons and electrons and 147 neutrons and a mass of 242.0595492 g/mol. It has a half-life of approximately 141 years, decaying:

1. 99.54% of the time by isomeric transition (with a decay energy of 0.05MeV) to its short-lived nuclear isomer americium-242
2. 0.46% of the time by emitting an alpha particle (the decay energy is 5.64 MeV) to turn into Neptunium-238
3. very rarely by spontaneous fission (halflife (9.5±3.5)×10¹¹ years)^[2]

^242mAm is fissile (because it has an odd number of neutrons) and has a low critical mass, comparable to that of plutonium-239.^[3] It has a very high cross section for fission, and if in a nuclear reactor is destroyed relatively quickly.

Another report claims that ^242mAm has a much lower critical mass, can sustain a chain reaction even as a thin film, and could be used for a novel type of nuclear rocket.^[4]

Americium-242 has a half-life of 16 hours. This is one of the rare cases when a lower-energy nuclear isomer is less stable than the higher-energy one. It decays:^[5]

1. 82.70% of the time, by beta decay to curium-242
2. 17.30% of the time, by electron capture to plutonium-242

[edit] See also

• Americium
• Isotopes of americium