A proportionality factor, known as the k factor is used to relate the characteristic X-ray intensities IA/IB in a thin sample to the actual concentrations in wt% in the form
CA/CB = KAB.IA/IB
where I = Intensity, and C = concentration.
K factors
The k-factor relates the intensity of two elements. Where more than two elements are to be analyzed, if all ratios are taken with respect to a single element (this is called the ratio standard element), these values can be regarded as elemental sensitivity factors, more usually known as k-factors.
The theoretical k factor value is determined using the X-ray line type (K series, L series, etc) for the ratio standard you select. For a given X-ray line, A, and ratio standard line, R, the k factor kAR is calculated as follows:
kAR = AA wR QB aR eR / AR wA QA aA eA
where A = atomic weight; w = fluorescent yield; Q = ionisation cross section; a = the fraction of the total line, e.g. Ka / (Ka +Kb ) for a Ka line, and e = the absorption due to the detector window at that line energy.
Once k factors are known relative to the ratio standard, any other k factors can be calculated using the formula
kAB = kAR / kBR
You can use any element if you are using theoretically derived k factors. Conventionally, Si is used.
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