There also need to be enough fissionable atoms about for the neutrons to bumpinto-in other words , a critical mass .

同时还需要足够多的、可裂变的原子核用于中子进行撞击，换句话说，需要一个临界质量。

Anuncontrolled chain reaction within a large amount of fissionable material canlead to an explosive release of energy , as in nuclear weapons .

大量的可裂变的材料中发生不受控制的链式反应就会导致爆炸以释放能量，这就是核武器的原理。