- #1

amjad-sh

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I am wondering why in all X-ray diffraction experiments used to probe or know the crystal structure of the solid they assume that the scattering process is elastic, e.g, if an X-ray with wave vector ##k\vec{n}## is incident on a sample, it will diffract with a wave vector ##k\vec{n}'## of same magnitude but different direction.

Bragg's formula is based on the assumption that the scattering of X-ray is elastic, and this formula, I guess, is used to unpack the structure of all crystalline solids. Therefore, I can deduce from this that X-ray scattering in all crystalline solids is elastic, because otherwise they wouldn't use Bragg's formula to analyze their structure.

Is the reason behind this that the potential ##V(\vec{r})## that describes the interaction between the X-rays and any crystalline solid is very weak? and if so, why is it so weak? In some references they use Fermi's golden rule to derive the Laue condition which is equivalent to Bragg's formula, and Fermi's golden rule can't be reliable unless the potential ##V(\vec{r})## is assumed very small, because it is a first order approximation.

Thanks.