For an initially unpolarized beam, the scattered beam intensity is reduced by a factor
I' = I(1 + cos2 (2 theta))/2 . For a beam that is initially polarized (for example, due to a monochromator crystal between the source and sample, or because the source is synchrotron radiation), the polarization correction becomes I' = I(A + Bcos2 (2 theta))/ where the coefficients A and B depend on the initial polarization of the beam and the azimuthal direction (chi) of the scattered beam relative to the initial polarization. (See, e.g., B. E. Warren, X-ray Diffraction, Addison-Wesley, 1969, or other elementary texts on x-ray diffraction). The user can correct for this effect by dividing the measured intensity by the correction factor. Note that the polarization effect is very small for a typical small-angle geometry, in which case one can safely leave A and B at their default values of 1.0 and 0.0; for other geometries the user should think carefully about exactly how to apply this correction since it does in principle depend on chi. |