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

When, through the occupation of the free orbital by an electron from the exterior
orbits the ionized atom comes back to its normal state, a secondary X radiation is
emitted, known as fluorescence radiation. The fluorescence radiation spectrum is
a spectrum of lines that is characteristic for the material subjected to the
radiation. From the equation it is obvious that the wavelength of the fluorescence
radiation Has higher value, than that, of the incoming radiation.
h
∆λ
= ⋅ 2
m ⋅ c
( 1− cos θ )
The incoherent scattering of the X rays. The incoherent scattering (or
Compton effect) was explained by A.H. Compton as an elastic collision between
an X photon and free or lose tide electron. During the collision, some of energy of
the incoming photon is passed to electron. After the collision, the energy of the
photon is slightly smaller. In consequence, scattered radiation has a wavelength
slightly bigger than that of the incoming radiation.
The coherent scattering of the X rays. Also, the scattering of the X rays by
electrons on an atom can take place coherently.
According to J. J. Thomson’s theory of coherent scattering, electron is put in
oscillating motion by incoming electromagnetic wave (the X radiation). In this
forced oscillating movement, with its frequency equal to that of the electric field
of the electromagnetic wave, electron is continuously accelerated or decelerated
and as a result of that it emits an electromagnetic wave having a wavelength the
same as incoming radiation.
Although X rays are scattered by the electron in all directions, the intensity of the
radiation according to J. J. Thomson’s equation, depends on the scattering angle:
⎛
I = I ⋅ ⎜ 0
⎝ r
2
e
⋅ m
4
2
⋅ c
4
⎞ ⎛ 2 2 ⋅θ
⎞
⎟ ⋅⎜1
+ cos ⎟
⎠ ⎝ 2 ⎠
In this equation, I0 represents the intensity of primary beam, I – the intensity of
scattered radiation, 2θ – the scattering angle.
⎛ 2 2 ⋅θ
⎞
The factor ⎜1+
cos ⎟
⎝ 2 ⎠
is called polarization factor due to the fact that
crystallographic planes play role of polarizator for X-ray.
5. Basics of Crystallography
A crystal consists of a periodic arrangement of the unit cell into a lattice. The unit
cell can contain a single atom, ion or molecular in a fixed arrangement.
Figure 6. : The structure of CsCl crystal
Physics of Advanced Materials Winter School 2008 8