FISCHER FISCHERSCOPE X-RAY 4000 Series, Operator'S Manual

Page: 91 / 170

Back-up cycle Mass per unit area and geometric coating thickness
FISCHERSCOPE
®
X-RAY 91
of the characteristic radiation of the coating material is determined
from the number of atoms within the excited sample volume.
The intensity of this radiation is higher as more atoms of the sample
volume are excited by the primary radiation and emit their radiation
to the detector.
However, the following applies to the radiation of the substrate
material:
The higher the intensity of the characteristic radiation of the
substrate material, the lower is the coating thickness.
Reason: The absorption of the substrate material radiation
penetrating the coating is lower through a “thinner” coating.
The same applies to multiple coatings and coatings comprised of
several elements.
Functional principle of X-ray fluorescence
Primary X-radiation (symbolized by black arrows) excites the
sample volume to be analyzed into emitting fluorescence radiation.
Each occurring element emits a characteristic energy (symbolized
by red or green arrows) that are registered separately by the
detector.
The following assumption is made for the quantitative computation
of these effects in the defined test area (sample volume) under the
surface to be measured (measurement spot):
The excited atoms are distributed homogeneously across the entire
volume, i.e., the specific density

of the material is constant in the
entire volume that is to be measured.