PERFORMANCE OF TXRF and GI-XRF ANALYSES - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 235

M α , respectively, can be separated by a WDS, but not by means of an EDS. The
combination of K β and K β does not occur at all.
The interference of K α and K β and vice versa can happen for neighboring
elements with Z 2 = Z 1 ± 1if19 28. The coincidence of Cr-K α and V-K β

( Δ E = 12 eV) and of V-K α and Ti-K β ( Δ E = 20 eV) are well-known examples.
A further overlap is possible for elements after next, that is, if Z 2 = Z 1 ± 2 and
35

Z 1

42. As an example, Y-K α and Rb-K β are separated by only 3 eV.
More complicated relations exist for the coincidence of K α peaks and L α peaks:
Z 2 ≈ 25/11

Z 1

30. Close interferences are produced by Ne-K α
and Ni-L α ( Δ E = 3 eV), by Al-K α and Br-L α ( Δ E = 6 eV), by S-K α and Mo-L α
( Δ E = 15 eV), and by As-K α and Pb-L α ( Δ E = 8 eV). The interference of L α by
M α occurs if Z 2 ≈ 26/15

Z 1 + 5if5 Z 1

49. Notorious examples are Y-L α
and Os-M α ( Δ E = 8 eV) as well as Zr-L α and Pt-M α ( Δ E = 8 eV). The K α lines
can even be disturbed by M α lines if Z 2 ≈ 25/6

Z 1 + 8.5 for 31 Z 1

19.
Particular examples are the line or peak coincidences of S-K α and Pb - M α
( Δ E = 38 eV) and Mg-K α and Tb-M α ( Δ E = 13 eV). The coincidences men-
tioned cannot even be separated by a powerful WDS with its good spectral
resolution.

Z 1 + 15 for 10 Z 1

4.3.1.2RegardofSumPeaks

At high count rates different pulses may be added and yield so-called sum
peaks. Such pulse pileup effects can be reduced by the pulse-pileuprejector as
already mentioned. If, however, the count rate exceeds the level of 10 5 cps, two
pulses may arrive less than 1 μ s apart. These nearly coincident pulses appear as
one single sum peak. In that case, the spectrum shows an additional peak that
corresponds to the sum of two photon energies E 1 and E 2 .
Of course, such peaks generally arise for main constituents of a sample,
either for two principal peaks of two main constituents or for one or two
principal peaks of only one main constituent. In general, they can be identified
as such and the net intensity of the individual peaks can be determined by a
simple mathematical approach.

4.3.1.3DealingwithEscapePeaks

The total effect is more of a problem during the identification of small trace-
element peaks overlapped by escape peaks caused by a strong mother peak of a
main component. It is less troublesome for silicon detectors than for germa-
nium detectors, where it poses difficulties throughout the important region of
X-ray spectra between 1 and 30 keV. However, these problems disappear if the
sample consists only of elements with mother peaks below 11 keV, for example,
if only lighter elements ( Z < 31) are present.
Escape peaks cause weaker problems as regards counting losses of the
mother peak. A correction is possible by the addition of the daughter peak to
the mother peak. As can be read from Figure 3.33, this correction is only about