X-RAY DIFFRACTION

X-Ray Diffraction. Diffraction is the bending or spreading of waves that encounterin ohjeet ta barrier or an opening) in their path. When light waves pass through a narrow they scattered in such a way that the wave seems to spread out. This physica phenomenon is called diffraction. For diffraction to occur, the size of the object must be if the order of the wavelength of the incident waves, when the wavelength is much small than the size of the object, diffraction is ordinarily not observed and the object casts a shars shadow.

When light passes through many evenly spaced narrow slits fa diffraction grating), the scattered waves interact to form a series of light and dark bands known as diffraction pattern. By studying these patterns, we can learn about the diffracting obje

X-rays are generated as a result of bombardment of cathode rays on anticathos target. X-rays are electromagnetic radiation with wavelengths of the order of 0.1mm, distance which is of the same order of magnitude as the molecular diameters in gases an the roughly estimated interatomic distances in a solid. Thus, a crystal can serve as an affective diffraction grating for X-rays. X-ray diffraction results from the scattering of X rays by a regular arrangement of atoms, molecules or ions.

The atoms in a crystal form reflecting planes for X-rays. When X-rays are reflected from these planes, they show a diffraction pattern, which can be recorded on photographic plate as a series of spots. By analyzing the diffraction pattern, we can determine the positions of each atom in the unit call of the crystal. X-ray diffraction is as important method for the study of the structure of solids. The instruments used to measure X-ray diffraction, known as X-ray diffractiometers, are now computer-controlled, making the collection of diffraction data highly automated. The diffraction pattern of a crystal can be determined very accurately and quickly. Computer programs are then used to analyze the diffraction data and determine the arrangement and structure of the molecule in a crystal.

 X-rays are shorter wavelength, high energy electromagnetic radiations, produced by bombarding a metal with high energy electrons. The high energy electrons interact with the inner electrons of the inner shells of the atoms of the metal. The collision knocks an electron out of an inner shell and an electron in a higher energy shell drops into the vacancy, emitting the excess of energy as a photon of higher energy.

 The internal structure of a crystal can be studied with the help of X-rays, since the wavelength of X-rays is of the same order (10 m) as the inter atomic distances in a crystal. Hence a crystal might be used as a diffraction grating for X-rays. Actually, thi diffraction of X-rays is due to the electrons of atoms present in a crystal. Max Von laur (1912) predicted that if a beam of X-rays is allowed to fall on a crystal, it should be transmitted through the crystal as a number of diffracted beams. If a photographic plates placed behind the crystal, the image obtained on the photographic plate would show a number of spots (laue spots). From a consideration of the position of these spots, one can reach at some conclusion about the position of atoms in the crystal and thus from these Laue patterns, the crystal structure can be constructed. The study of crystal structure with the help of X-rays is called X-ray crystallography

 

The characteristics of an X-ray diffraction pattern are related to the structure of the crystal; the wavelength of the X-rays and the angle at which the radiation strikes the crystal.