Quantification with M-Quant
158
User Manual
The calculation of the correction factors uses the following procedures.
Table 58 Calculation of correction factors
Calibration type Description
Optic calibration The X-ray optic has an influence on the excitation spectrum. The tube
spectrum can be calculated by theory. However, there is no possibility
for a calculation of the optic influence. The transmission function of the
optic is changing from optic to optic and even depends on the
mechanical alignment of the optic. Therefore the transmission function
has to be determined in the aligned instrument.
The transmission function of the optic is approached by an asymmetric
Gaussian function.
Since the energy distribution of the excitation radiation is required for the
calculation of intensities this part needs to be determined in a first step.
For that purpose the K-lines of pure element spectra are used. The
correction factors are calculated iteratively. The target is to achieve the
best Chi²-value for the deviations of concentrations.
This calibration needs to be performed only once.
If the optic is new aligned in the instrument the optic calibration has to be
repeated.
Sensitivity calibration For the calibration of sensitivity several pure elements and stoichiometric
compounds with both K- and L-lines has to be measured. The target is to
get concentrations that have a very small deviation from the given
values.
These element dependent correction factors are fitted by a polynomial
function to get correction factors for all energies.
The energy range of the polynomial function and its order can be
selected during calibration. M-lines are not used for quantification.
Pileup calibration The high excitation efficiency of X-ray optics generates count rates
higher than 200 kcps or even 300 kcps. In that case strong pile up peaks
are generated. They have to be corrected either to avoid not correct
element identification or to avoid not correct peak intensity determination
in case of overlapping of pile up peaks with fluorescence lines.
Pile up peaks are generated according to
I
pile up
= τ (E) ∗ I
moth1
∗ I
moth2.
The calculation of pile up peaks in the spectrum is performed with that
relation. For that purpose the factor τ (E) is required. The determination
of this coefficient requires spectra of pure elements with high intensities.
Their pile up peaks has to be in the measured energy range.
This spectrum is subtracted from the measured spectrum to correct the
pile ups.
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