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critical mass
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Tweet n. 1. The smallest mass of a fissionable material that will sustain a nuclear chain reaction at a constant level. 2. The total mass of matter needed to generate sufficient gravitational force to halt the current expansion of the universe. 3. An amount or level needed for a specific result or new action to occur: "[Plastic bags are] so nearly weightless that it's difficult to gather enough of a critical mass to make recycling them economically worthwhile" (Susan Freinkel). |
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