5.5. PAP Corrections
PAP is a general model for calculating X-ray intensities. Unlike ZAF, which is conceived as a matrix correction proceedure, PAP is a general model for the calculation of X-ray intensities. It can be used for a wide range of X-ray energies (100 eV to greater than 10 keV) and accelerating voltages (1-40 keV). The improvement over ZAF results from using better expressions for the Z effects (backscattering factor, retardation of the electrons, and effective ionization cross-section). PAP also does a better determination of the absorption effects. It calculates the intensity of the radiation emitted from the sample using a modified version of the f(rZ) polynomial used in standard ZAF correction scheme that better that better fits the experimentally determined X-ray distribution (Figure 5.5).
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Figure 5.5. Depth distribution of Mg-Ka in aluminum at 25 keV. Comparison of theoretical functions with experimental results of Castaing and Henoc (after Pouchou & Pichoir, 1984). |
Although PAP takes slightly longer to calculate than ZAF, the improvement is well worth it.