Critical mass

Critical mass is a term used in nuclear physics to describe the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties, its density, its shape, its enrichment, its purity, its temperature, and its surroundings.

Nuclear Physics

In nuclear physics, the critical mass is the minimum amount of nuclear material needed to make a nuclear bomb. It is the amount needed for a sustained nuclear chain reaction. The critical mass of a nuclear material depends on its nuclear properties (e.g., the nuclear fission cross-section), its density, its shape, its enrichment, its purity, its temperature, and its surroundings.

Fissile Material

Fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons (i.e., a thermal system) or fast neutrons.

Nuclear Chain Reaction

A nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g., uranium-235, 235U).

See Also

• Nuclear fission
• Nuclear reactor
• Nuclear weapon
• Uranium
• Plutonium

References

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  Partially reflected plutonium sphere

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  Critical mass

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  Nuclear predetonation