critical mass

1. Physics. the amount of a given fissionable material necessary to sustain a chain reaction at a constant rate.
2. an amount necessary or sufficient to have a significant effect or to achieve a result: a critical mass of popular support.
[1940-45]

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Minimum amount of a given fissionable material necessary to achieve a self-sustaining nuclear chain reaction under specified conditions.

Critical mass depends on several factors, including the kind of fissionable material used, its concentration and purity, and the composition and geometry of the surrounding reaction system.

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      in nuclear physics, the minimum amount of a given fissile material necessary to achieve a self-sustaining fission chain reaction under stated conditions. Its size depends on several factors, including the kind of fissile material used, its concentration and purity, and the composition and geometry of the surrounding reaction system.

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Universalium. 2010.

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