重水之所以重是因为水中氢的重量是普通氢的两倍（它的原子核中有一个质子和一个中子，而不仅仅是一个质子）。

Heavy water is heavy because the hydrogen in it weighs twice as much as ordinary hydrogen (it has a proton and a neutron in its nucleus, instead of just a proton).

youdao

普通氢非常，非常缓慢即使在一个地方像在太阳中心一样无法想像的热。

Regular hydrogen fuses very, very slowly even in a place as unimaginably hot as the center of the sun.

youdao

科学家用到了一种叫离子显微镜的仪器，来比较月球岩石上氢的含量与重氢含量（重氢比普通氢多带有一个中子）。

The researchers used what’s called an ion microscope to compare the amount of normal hydrogen in the moon rocks to the amount of the hydrogen isotope deuterium, which carries an extra neutron.

youdao