Section 19.5.6.2. Intensity correction

Data intensities must be corrected for geometric and polarization effects (Fraser et al., 1976; Millane & Arnott, 1986). The geometric correction has two components: a factor due to the geometry of the intersection between the diffraction pattern in reciprocal space and the sphere of reflection, and a factor due to the angle of incidence of the diffracted beam on the detector. The first factor is analogous to the Lorentz factor in crystallography, which arises because of the time taken for a reflection from a moving sample to pass through the Ewald sphere. The geometric correction can be applied to each data point as a single correction (Fraser et al., 1976); this is the simpler procedure for diffraction from noncrystalline fibres. For crystalline fibres, it is often convenient to apply Lorentz and polarization corrections to each data point, to integrate the intensities within each reflection, and then to apply the remaining geometric corrections (Millane & Arnott, 1986). The Lorentz correction is where θ is the Bragg angle and (Millane & Arnott, 1986). The polarization correction is Intensities should be divided by Lp. Intensities may also be corrected for nonlinearity of detector response and for absorption by the specimen and by detector components.