Polarisation factor

The polarisation factor, C=D g. D j,. This is unity for polarisation, in which the electric field vector is perpendicular to the dispersion plane and cos(2 g) for polarisation in which the electric field vector lies in the dispersion plane. We may apply equation (4.20), which since h is real implies that Im(K o)=Im(K ), and, in order to express the solution simply, introduce the very important idea of deviation parameters, g and. These express the deviation of the incident and diffracted wavevectors from the kinematic assumption where k g = k ij =l/, and are defined as... 

The conditions for the data collections are summarized in ref. The intensities of selected reflections [I > 2cr(I)] were corrected for Lorentz and polarisation factors but not for absorption. 

The Lorentz and polarisation factors are usually combined, for powder X-ray diffraction, into a single correction term ... 

In the case of an unpolarised incident beam (such as a conventional X-ray source beam without monochromator) the polarisation factor is given by... 

Here, d//dA denotes the spectral intensity distribution of the incident X-ray beam V is the volume of sample illuminated V0 is the sample unit cell volume 0 is the Bragg angle for the reflection h P is the polarisation factor A is an absorption correction for the sample in its capillaiy and D is a detector sensitivity and obliquity factor. Quantities such as P, A and D vary with any or all of A, 0 and x, the position of the diffracted beam on the detector the spectral intensity distribution is, in general, not precisely known in advance and the detector may suffer from spatial distortion and non-uniformity. Thus equation (7.17) may be written as... 

FIGURE 3. Instrumeiit effective area and polarisation factor as a function of energy... 

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