critical mass

1. N-SING In physics, the critical mass of a substance is the minimum amount of it that is needed for a nuclear chain reaction. 临界质量[技术] [also no det]

In order to make a nuclear explosion, the critical mass must come together within a fraction of a millionth of a second. 为促成一次核爆炸，临界质量必须在一百万分之一秒内聚集在一起。

2. N-SING A critical mass of something is an amount of it that makes it possible for something to happen or continue. 临界数量[also no det]

Only in this way can the critical mass of participation be reached. 只有这样才能凑足参加人数。