Nuclear material, containing a high proportion of fissile isotopes, which is essential for making nuclear explosives. High-enriched uranium (HEU) and weapons-grade plutonium are examples of fissile material. See; Fission.

Material whose nucleus can be fissioned when it absorbs a low-energy (ideally zero energy) neutron. Fissile materials can sustain nuclear chain reactions.

a material made up of heavy atoms that can be split into pieces emitting energy.

The nuclear materials, such as U-235 and Pu-239, that are used to make nuclear weapons. U-235 is the only naturally occurring fissile isotope (see Enrichment).

nuclei that undergoes fission when a neutron is absorbed.

any material in which neutrons can cause a fission reaction. The three primary fissile materials are uranium-233, uranium-235, and plutonium-239.

Any material fissionable by thermal (slow) neutrons; the two primary fissile isotopes are uranium-235 and plutonium-239.

material capable of sustaining a fast-neutron chain reaction. This chain reaction is a series of events in which atomic nuclei are split in two and release neutrons in the process. These neutrons, in turn, cause other nuclei to split and release more neutrons, thereby perpetuating the reaction. Fissile material can be used in the fission core of a nuclear reactor or in a nuclear explosive.

Material composed of atoms that fission when irradiated by slow or "thermal" neutrons. The most common are uranium 235 and plutonium 239. The term is often used to describe plutonium and HEU, e.g., a cutoff in the production of fissile materials. Uranium 233 is also fissile.

material fissionable by slow neutrons. The fission process and the fissile isotopes are the source of energy in nuclear weapons and nuclear reactors.