The number of these waves passing a given point in one second is the refractive index . We can imagine all the wavelengths of radiant energy as upon a giant radio-dial. We can segment this dial by wavelength. And beyond X-rays there are still shorter waves known as krypton radiation. The penetrating power of X-rays seems magical to us.
Atoms consist primarily of open space.
It may help to compare an atom with our own solar system. What really matters is the size of the object you wish to pass through. An object greater than 93 million miles in diameter would never make it. In the case of atoms, waves of X-ray size often can. As you might imagine, sometimes a given ray is on a collision course with the nucleus or perhaps one of the electrons of an atom.