Why do high energy waves e.g. X-rays get refracted very little?

Question

Correct me if I am wrong but since refractive index is directly proportional to frequency, this would mean that higher frequencies would have higher refractive indexes i.e should bend more but i have come to know that higher energy waves like X-rays get refracted very little. Which statement is correct?

Pieter · Answer

One way to see this is that x-ray frequencies are far above the frequencies of the Lorentz oscillators that are used to explain the dispersion of transparent substances. Those resonant frequencies are in the UV.
X-ray frequencies are far higher. The phase shift differs by 180 degrees from below the resonance, and this results in an index of refraction slightly smaller than unity. That is why there can be total external reflection at surfaces for shallow angles in x-ray optics.

Why do high energy waves e.g. X-rays get refracted very little?

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