BRAGG’S Law for X-ray diffraction
where, d is the spacing of the planes and n is the
order of diffraction.
• Bragg reflection can only occur for wavelength
The diffracted beams (reflections) from any set of
lattice planes can only occur at particular angles
predicted by the Bragg law.
• The diffracted beams are found to occur when
the reflections from planes of atoms interfere
• When path difference is equal to wavelength.
ROTATING CRYSTAL METHOD
In the rotating crystal method, a
single crystal is mounted with an
axis normal to a monochromatic
x-ray beam. A cylindrical film is
placed around it and the crystal is
rotated about the chosen axis.
As the crystal rotates, sets of lattice planes will at some
point make the correct Bragg angle for the monochromatic
incident beam, and at that point a diffracted beam will be
Structure of DNA
This X-ray crystallography image of DNA shows a pair
of strong arcs along the vertical axis. Such pictures
gave Rosalind Franklin clues about the double helix
structure of DNA, but they do not reveal the
interactions between the crystallized protein and
Application of XRD
XRD is a nondestructive technique. Some of the uses of x-ray
• Application in pharmaceuticals.
• Application in determination of protein
Advantages and disadvantages of
• X-ray is the cheapest, the most convenient and widely used
• X-rays are not absorbed very much by air, so the specimen
need not be in an evacuated chamber.
• They do not interact very strongly with lighter elements.
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