Modifications of the diffraction pattern

The diffraction pattern is affected by various factors that depend on crystal quality and experimental conditions. These will be examined in turn. 

The simplest type of crystal diffraction, and that considered here, is called kinematical diffraction. In such diffraction the X-ray beam, once diffracted, is not further modified by additional diffraction in its passage through the crystal. The phase differences between radiation scattered at different points in the crystal depend only on differences in the path lengths of the incident and diffracted waves. The summation of these waves with the appropriate amplitudes and relative phases determines the intensities. 

The structure factor F hkl) is the Fourier transform of the unit cell contents sampled at reciprocal lattice points, hkl. The structure factor amplitude (magnitude) F is the ratio of the amplitude of the radiation scattered in a particular direction by the contents of one unit cell to that scattered by a single electron at the origin of the unit cell under the same conditions (see Chapter 3). The first report of the structure factor expression was given by Arnold Sommerfeld at a Solvay Conference. The structure factor F has both a magnitude F(hkl) and a phase rel- 

FIGURE 6.20 (cont d). (c) Structure factors for NaCl (black) and KCl (white). 

To compute F hkl) when atomic coordinates Xj, yj, Zj for each atom j are known  

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