20-07-2012, 11:29 AM
X Ray diffraction
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DISCOVERY OF X-rays
HOW?
While working with a discharge tube he found that Barium Platinocyanide screen placed near it began to glow.
Nature was not known they were called X-RAYS.
WHAT ARE X-rays?
X-ray, invisible, highly penetrating Electromagnetic radiation of much shorter wavelength (higher frequency) than visible light. The wavelength range for X rays is from about 10-8m to about 10-11m, the corresponding frequency range is from about 3×1016 to about 3×1019Hz.
Properties of X-rays
They are electromagnetic radiations of very small wavelength.
They travel with the velocity of light. i.e. 3x10-8m/s
They affect the photographic plates.
Not deflected by magnetic or electric field and therefore do not posses any charge.
Ionize the gas through which they pass.
Highly penetrating and can pass through many solids which are opaque to visible light.
e.g. wood, paper, cardboard.
Principles of X-ray diffraction
X-rays are passed through a crystalline material and the
pattern produced give information of size and shape of
the unit cell.
X-rays passing through a crystal will be bent at various
angles: this process is called Diffraction.
X-rays interact with electrons in matter, i.e. are
scattered by the electron clouds of atoms.
The angles at which x-rays are diffracted depends on
the distance between adjacent layers of atoms or ions.
X-rays that hit adjacent layers can add their energies
constructively when they are “in phase”. This produces
dark dots on a detector plate
COLLIMATOR
The X-rays produced by the target material are randomly directed. They form a hemisphere with a target at the center.
In order to get a narrow beam of X-rays, the X-rays generated by the target material and allowed to pass through a collimator which consists of two sets of closely packed metal plates separated by a small gap.
The collimator absorbs all the X-rays except the narrow beam that passes between the gap.