The Röntgen Radiation and its application in studies of ... - Mansic

Due to the fact that Kβ and Kα2 are diffracted on the same crystallographic plane,
they cause appearance of additional peaks in XRD pattern. Such inconvenience
can be easy eliminated by adding filters.
4. Interaction with matter
The absorption of the X rays
Figure 5. An atom from the material of the anode
One of the important properties of X-rays is their ability to pass through opaque
substances. At the passing of X-rays through a substance, their intensity is
reduced and for monochromatic radiation the next equation can be written:
I = I 0 ⋅ e
Where: I0 is the intensity of a primary beam, I – the intensity of the transmitted
radiation through an absorbent shield, x- thickness of absorbent and µ – linear
absorption coefficient.
Due to the fact, that the linear absorption coefficient depends on the physical
status of the X ray absorbing substance, the µ/ρ mass absorption coefficient is
introduced which, for a monochromatic beam, is a constant, independently on the
nature of absorbent material [4]. Thus, the graphite and the diamond, as
allotropic variations of carbon, have different values for their linear absorption
coefficients, but both have the same value of the mass absorption coefficient.
Physics of Advanced Materials Winter School 2008 7
−µ
x
The secondary fluorescence. The Auger effect
The X rays beam, which passes through a substance, can cause several effects:
fluorescence, scattering of X-ray (coherent and incoherent-Compton effect),
increase of the heat and electrons (recoil electrons and photoelectron).
One of these effects, discussed above, is the secondary fluorescence that consists
in the emission of an X ray characteristic spectrum as a result of the atoms
passing in an excited state due to their interaction with the incoming X-ray
photons. When an X ray photon of a certain energy collides with a target atom,
an electron from the interior orbits of the atom is expulsed and the energy of the
absorbed photon can be found as excitation energy of the ionized atom and as
kinetic energy of the expulsed photoelectron:
mv
h Eleg
2
+ = ⋅ϑ
(Eleg represents the bounding energy of the expulsed photon).
2