I guess also for clarity - in the data given above - its important to mention that it does not matter that the modelled material which the beam is hitting contains a small and possibly different about of Ca - for the calczaf correction subtracts the amount of Ca generated by secondary fluorescence.
Hi Ben,
That is actually a very good point. I hadn't quite considered that implication, but you are correct.
As you said, in CalcZAF (and soon PFE!), the correction for secondary fluorescence by a boundary phase is based on the contribution only from the boundary material. Therefore the beam incident material's composition only matters so far as the production of characteristic and continuum x-rays produced by the beam incident phase stimulates secondary fluorescence in the boundary material.
That said, it is important when subtracting larger secondary fluorescence effects to perform this correction during the sample matrix iteration, because if you are subtracting 2 or 3 wt% of an SF artifact from your sample matrix, the quant matrix correction needs to be recalculated, and especially if the fluoresced element is one of the elements in an interference correction.
For example, if you are measuring trace Ni in a Cu alloy adjacent to a Co rich phase, you will measure a large Co signal (up to 4 wt.%) near the Cu-Co boundary and since Co Ka/Kb interferes with Ni Ka, you would be over correcting the interference correction of Co on the trace Ni in the Cu alloy.
However, since I implemented both the spectral interference correction and the secondary boundary fluorescence correction within the matrix iteration, all these issues are handled automatically!
john