Fissile material

[1] A self-sustaining thermal chain reaction can only be achieved with fissile material.

Under this definition, the only nuclides that are fissionable but not fissile are those nuclides that can be made to undergo nuclear fission but produce insufficient neutrons, in either energy or number, to sustain a nuclear chain reaction.

[6] These are materials that sustain an explosive fast neutron nuclear fission chain reaction.

[7] The fast fission of 238U also makes a significant contribution to the power output of some fast-neutron reactors.

No fission products have a half-lifein the range of 100 a–210 ka ... ... nor beyond 15.7 Ma[12] In general, most actinide isotopes with an odd neutron number are fissile.

These "even-even" isotopes are also less likely to undergo spontaneous fission, and they also have relatively much longer partial half-lives for alpha or beta decay.

The relatively short half-life of such odd-odd heavy isotopes means that they are not available in quantity and are highly radioactive.

[note 1] To be a useful fuel for nuclear fission chain reactions, the material must: Fissile nuclides in nuclear fuels include: Fissile nuclides do not have a 100% chance of undergoing fission on absorption of a neutron.