EDAX EDS Manual

Quantitative Analysis with SEC factors --Hans Dijkstra
For microanalysis the composition of a sample can be calculated from the measured X-ray
intensities using:
Meas
W Z A F I
% = • • •
I
Where Z, A and F are the matrix correction parameters, describing the atomic number effect
(stopping power and backscatter effect), the absorption effect, and the fluorescence effect.
Since for standardless analysis we have no Ι STD available, EDAX has chosen to use calculated
standards, with in a simplified form:
N
I n p f
A R
Q E
dE d s dE
0 E j
Std Ω
j ( )
Calculated = εεεε dωωωω j jl ( χχχχ)
����
4ππππ
E / ( ρρρρ )
0
Where n is the number of electrons entering the sample, Ω/4π is the solid angle, ε is the detector
efficiency, ω is the X-ray fluorescence yield, p is the relative probability for the transition involved,
f(x) is the absorption correction, and the integral represents the cross-section of the ionization
involved. Since n is unknown, and thus set to 1, the calculated intensity might be in a totally
different order of magnitude as the measured intensity. Normalizing the W% to 100% solves this
problem.
This function seems to work rather accurate, but it is important to notice that some factors are left
out of the calculations, like the solid angle, since this is a constant factor and this equation is only
used for standardless analysis, i.e. the results are normalized to 100% anyway.
One disadvantage of this equation is that εd, the detector efficiency, can not be predicted with
sufficient accuracy for X-ray lines below 1 keV. Small variations in detector quality (Si dead layer,
etc.) can cause variations in measured intensity. Therefore EDAX has introduced the SEC factors.
The final equation now becomes:
I
W% = Z • A•F •
SEC •
I
The SEC factors can simply be calculated by entering a compound standard, and calculate the SEC
from the given W% (thus the ZAF factors and the standard intensity can be calculated) and the
measured intensities. Also in this procedure calculated SEC factors may be off by an order of
magnitude, and now this is solved by assuming one SEC factor to be identical to a default value
(thus keeping it fixed), and scaling other SEC factors relative to the fixed one.
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EDAX Training Course –Quantitative Analysis with SEC Factors - page 1
Meas
Std
Std
Calculated