Use Empirical Alpha-Factors
To utilize empirically determined Alpha-Factor terms, simply edit the EMPFAC.DAT file in the Probe for EPMA program data directory (usually C: \ProgramData\Probe Software\Probe for EPMA). If an Alpha-factor entry in the file matches the run conditions of the current run, it can be used to overwrite the previously internally calculated alpha-factor terms. The format of the EMPFAC.DAT file is described below :
52.5 20.0 1 "au" "la" "ag" 1.142 0.000 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 1 "ag" "la" "au" 1.483 0.000 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 1 "au" "la" "cu" 1.347 0.000 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 1 "cu" "ka" "au" 0.758 0.000 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 2 "au" "la" "ag" 1.159 -0.056 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 2 "ag" "la" "au" 1.505 -0.071 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 2 "au" "la" "cu" 1.347 -0.014 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 2 "cu" "ka" "au" 0.759 -0.007 0.000 "NBS Spec. Pub. 260-28"
52.5 20.0 3 "au" "la" "ag" 1.121 0.127 -0.179 "NBS Spec. Pub. 260-28"
52.5 20.0 3 "ag" "la" "au" 1.458 0.170 -0.247 "NBS Spec. Pub. 260-28"
52.5 20.0 3 "au" "la" "cu" 1.332 0.061 -0.075 "NBS Spec. Pub. 260-28"
52.5 20.0 3 "cu" "ka" "au" 0.740 0.089 -0.096 "NBS Spec. Pub. 260-28"
Each line contains a single empirical alpha-factors fit for half of a binary pair (one emitter-absorber system per line) for various take-off angles, operating voltage, elements, x-ray lines, etc.
Columns 1 and 2 contain the takeoff angle (degrees) and operating voltage (keV) that the alpha-factor was measured at. Column 3 is the fit flag (1 = constant expression, 2 = linear fit and 3 = polynomial fit). Columns 4 and 5 are the emitter element symbols and x-ray lines. Column 6 is the absorber element symbols. Note that Probe for EPMA only supports the use of elemental alpha-factors, i.e., referenced to elemental end-members as opposed to oxide end-members.
The three remaining columns are the alpha-factor terms. Note that constant alpha-factors have only one term, linear alpha-factors have two terms and non-linear or polynomial fit alpha-factors have three terms. For the non-linear alpha-factors, the first term is the intercept, the second term is the slope and the third term is the curvature term.
Empirical alpha-factors are calculated from experimentally measured k-ratios using a set of known binary (two element) standards covering a range of composition, by fitting the concentrations and intensity data to a plot of α vs. C, where C represents the standard concentrations and α is defined by the following expression :
Each binary data set can be fit to any or all of the alpha-factor fits, that is, constant (single term at 50/50 composition), linear (two terms) or polynomial (three terms).