1N-SING (核链式反应的)临界质量 In physics, the critical mass of a substance is the minimum amount of it that is needed for a nuclear chain reaction. (核链式反应的)临界质量 [technical]
2N-SING (某事发生或继续所需的)足够数量 A critical mass of something is an amount of it that makes it possible for something to happen or continue. (某事发生或继续所需的)足够数量
Only in this way can the critical mass of participation be reached. [+ of]