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。

In order to make a nuclear explosion, the critical mass must come together within a fraction of a millionth of a second.

《柯林斯英汉双解大词典》

1微秒就是一百万分之一秒。

A microsecond is a millionth of a second.

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没错，一微米是一百万分之一米，人类头发的宽度大概是100微米。

To put that into some sort of perspective, a micro-metre is a millionth of a metre; the width of a human hair is about 100 micro-metres.

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