that's one way to think about it, and there's also another way, and this is the way that your book presents it. If you, in fact, have two of the same atom right next to each other, let's say you have a crystal, or let's say you're talking about a metal, what you can do is just look at the distance between the two nuclei, and split that in 1/2, and take the atomic radius that way.

这只是一种定义的思路，另外还有其它方法，也就是你们课本上的方法，如果你，事实上，有两个相同的原子彼此靠在一起，比如说你有一个晶体，或者说你讨论的是一个金属，你所要做的就是,看看这两个原子核之间的距离，然后将距离除以二，就得到了这个原子的半径。

麻省理工公开课 - 化学原理课程节选

They took a crystal, this is a single crystal of nickel that has regular planes of atoms, and those planes are spaced on the order of an angstrom or less apart, and they irradiated this with x-rays.

他们取了个晶体,一个具有规则原子平面的，镍晶体,这些面间距差不多也是一埃或者更少，它们放射出X射线。

麻省理工公开课 - 固态化学导论课程节选