We have seen that Eq (19.3) gives the scattering factor of an atom or an ion in terms of its electron density. This scattering factor is a function of the wave - vector
, which gives the vector in the direction of the propagation of the wave. The magnitude of this vector is k. From an analysis of Eq (19.3) we find that fA is greatest in the forward direction and smaller in other directions. A sketch of fA as a function of k is given in Fig 19.3.
Figure 19.3 Scattering factors of atoms as a function of angle (k).
As k
0, sin ( kr ) / kr 1 (as the
) and fA is equal to the number of electrons in the atom /ion (Ne)
As k0, fA =
(19.5)
From the above discussion, we conclude that very good results for diffraction can be obtained for smaller values of
(as scattering factors are large). Also since the scattering factor of hydrogen is very small for all values of k, it is very difficult to infer about the location of hydrogen atoms through X - ray diffraction.
, which gives the vector in the direction of the propagation of the wave. The magnitude of this vector is k. From an analysis of Eq (19.3) we find that fA is greatest in the forward direction and smaller in other directions. A sketch of fA as a function of k is given in Fig 19.3. 
0, sin ( kr ) / kr 
) and fA is equal to the number of electrons in the atom /ion (Ne)
(as scattering factors are large). Also since the scattering factor of hydrogen is very small for all values of k, it is very difficult to infer about the location of hydrogen atoms through X - ray diffraction.
