Does anyone know of any references that are used in the sections of   the manual that talk about scattering from an arbitrary structure?

I'm looking for an easy to undertand, reasonably detailed explanation of how materials studio calculates the x ray scattering but this section of the help files seems very fragmented to me and so quite difficult to understand. Something more than just 'the fourier transform of the radial distribution functions' would be nice.

Any help is appreciated.