Section $37\mathrm{.}5$ talks about diffraction of X$-$rays from crystals of atoms. Why do you suppose this effects occur for X$-$rays, and not other types of electromagnetic radiation?

Only X$-$rays can have diffraction patterns, all other waves are really particles which can't diffract

Only X$-$rays can penetrate at all inside substances; even glass absorbs some light

Only X$-$rays have wavelengths comparable to the spacing of atoms

It works fine for any type of electromagnetic waves, but X$-$rays are the easiest and safest type of radiation to produce in a laboratory