critical mass

critical-mass的词性：
n.（名词）

1. The smallest mass of a fissionable material that will sustain a nuclear chain reaction at a constant level.
临界质量：裂变物质在恒量水平下能维持链式核反应的最小质量

2. A very important or crucial stage:
极其重要的阶段，极其关键的阶段：

“The sudden national uproar over drugs and drug abuse has reached politically critical mass in Washington”(Tom Morganthau)
“毒品和吸食毒品引起的全国性的突然骚乱在华盛顿到了政治上的关键性时刻”(汤姆·摩根叟)