X-ray diffraction

Diffraction of x-rays by crystals:

     X-rays can be diffracted by crystals in the same way as the visible light is diffracted by a diffraction grating. So crystal can act like diffraction gratings. The idea that crystals can diffraction x-rays was given by  Von laue .

   X-rays form part of the electromagnetic spectrum which were discovered by Roentgen. From the optical properties of x-rays , Sommerfeld estimated that the wavelength of x-rays is about 10^-10m. Crystalographers has estimated from a knowledge of density and molecular mass that spacings between two lattice points in a crystal is also about 10^-10m. From these two physical facts it occurred to max Von laue that crystals serve as diffraction gratings for x-rays and show the phenomena of diffraction. He took the help of his colleagues Friedrich and knipping.

X-rays were used for demonstration of diffraction in crystal due to the fact that the wavelength of x-rays is comparable to the interatomic spacing in actual crystal. Visible or ultraviolet light has larger wavelength and radiation of shorter wavelength like Gama rays are diffracted through very small angles which are difficult to measure.

Thus a crystal diffracted x-rays because x-rays  are scattered elastically without change of wavelength by charged particles of the atoms in crystal.

When x-rays fall on a crystal , the electrons present in the atoms stars vibrating with a frequency equal to that of incident x-rays beam under the effect of the electric field of the radiation. These electrons undergo acceleration and the accelerated electrons emit secondary radiation of the same frequency as that of the incident x-rays . The secondary x-rays diffract in all directions. When x-rays have large wavelength equal to that of the atomic dimensions all the radiation emitted by the electrons shall be in phase . On the other hand , if the incident x-rays have the same order of wavelength as that of the atomic dimensions, then the radiation emitted by the electrons are out of phase with one another. These radiation may , therefore exibit constructive or destructive interference producing Maxima or minima in certain directions. Thus , crystal shows diffraction pattern when x-rays fall on the crystal.