Critical mass

Smallest amount of fissile material needed to sustain a nuclear reaction

In nuclear engineering, critical mass is the minimum mass of the fissile material needed for a sustained nuclear chain reaction in a particular setup. The critical mass of a fissile material depends upon its nuclear cross section, density, shape, enrichment, purity, temperature, and surroundings. It is an important parameter of a nuclear reactor core or nuclear weapon and is important in nuclear weapon design.

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