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

The next improvement was introduced by William David Coolidge in 1913. He
invented the X-ray tube with heated cathode. The tube is vacuumed and the
cathode emits electrons through the heating with an auxiliary electric current.
The cause of the electrons emission is not the bombardment with electrons as it
was in the previous cases. The acceleration of the electrons emission process is
done by applying a high tension electric current, through the tube. When the
voltage increases, the wavelength of the radiation decreases.
The American physicist Arthur Holly Compton (1892 - 1962), a Nobel Prize winner,
discovered through his studies the so-called Compton Effect in the year 1922. His
theory demonstrates that the wavelengths of the X and gamma radiations
increase. This phenomenon also proves the particle-like nature of the X rays.
In 1913, physicists: Sir W. H. Bragg and his son Sir W.L. Bragg developed a
formula, which explains diffraction effect when crystals reflects X-ray beams at a
certain incidence angle (theta, θ). Now it is known as Bragg’s Law:
2 ⋅ d hkl ⋅ sinθ
= n ⋅ λ
⋅ λ
=
2 ⋅sinθ
n
d
The variable d is an interplanar distance between atomic layers in a crystal, and
λ is the wavelength of the X-ray beam; n is an integer. This observation is an
example of X-ray wave interference, commonly known as X-ray diffraction (XRD),
and was direct evidence for the periodic atomic structure of crystals postulated
for several centuries.
The Braggs were awarded the Nobel Prize in physics in 1915 for their work in
determining crystal structures beginning with NaCl, ZnS and diamond. Although
Physics of Advanced Materials Winter School 2008 3