The first subsection of Q1 of the 2012 exam paper asks why the X-ray scattering amplitude is proportional to the number of bound electrons in the atom, to a reasonable approximation.
The examiner's report comments that very few students picked up the marks for this. It mentions Thomson scattering as the mechanism - a photon scattering from a free particle, which the bound electrons can be considered to be since photon energy>>electron binding energy(?)
But I don't see why this precludes scattering from free electrons, which are actually free?
Or why this implies proportionality to the number of bound electrons?
Perhaps you could clarify for me?
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