The plutonium isotopes listed below are “fissionable,” which means that the nuclei can be split into two fragments, called fission products. In addition to being fissionable, plutonium-239 and plutonium-241 are “fissile” – that is, they can be split by neutrons of very low (ideally zero) energy. This means that they can be assembled into a critical mass, and hence can sustain a chain reaction without an external source of neutrons. To help you learn more about the properties of Plutonium, check out this worksheet on Plutonium!

Important Radiological Properties of Plutonium Isotopes
Pu-238 Pu-239 Pu-240 Pu-241 Pu-242
Half-life (in years) 87.74 24,110 6,537 14.4 376,000
Specific activity (curies/gram) 17.3 0.063 0.23 104 0.004
Principal decay mode alpha alpha alpha and some spontaneous fission [1] beta alpha
Decay energy (MeV) 5.593 5.244 5.255 0.021 4.983
Radiological hazards alpha and weak gamma alpha and weak gamma alpha and weak gamma beta and weak gamma [2] alpha and weak gamma
How isotope is produced nuclear reactors nuclear reactors nuclear reactors nuclear reactors nuclear reactors
Main uses Production of thermoelectric power used in nuclear weapons, satallites, and
heart pacemakers
Fissile material for nuclear weapons, and for the production of
none none none

Source: CRC Handbook of Chemistry and Physics, 1990-1991. Various sources give
slightly different figures for half-lives and energies.


  1. Source of neutrons causing added radiation dose to workers in nuclear
    facilities. ↩ Return
  2. Plutonium-241 decays into Americium-241, which is an intense gamma emitter. ↩ Return