# X - determined The two diagrams below can help to...

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X-ray diffraction Things that look a lot like diffraction gratings, orderly arrays of equally-spaced objects, are found in nature; these are crystals. Many solid materials (salt, diamond, graphite, metals, etc.) have a crystal structure, in which the atoms are arranged in a repeating, orderly, 3-dimensional pattern. This is a lot like a diffraction grating, only a three-dimensional grating. Atoms in a typical solid are separated by an angstrom or a few angstroms; . This is much smaller than the wavelength of visible light, but x-rays have wavelengths of about this size. X-rays interact with crystals, then, in a way very similar to the way light interacts with a grating. X-ray diffraction is a very powerful tool used to study crystal structure. By examining the x-ray diffraction pattern, the type of crystal structure (i.e., the pattern in which the atoms are arranged) can be identified, and the spacing between atoms can be
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Unformatted text preview: determined. The two diagrams below can help to understand how x-ray diffraction works. Each represents atoms arranged in a particular crystal structure. You can think of the diffraction pattern like this. When x-rays come in at a particular angle, they reflect off the different planes of atoms as if they were plane mirrors. However, for a particular set of planes, the reflected waves interfere with each other. A reflected x-ray signal is only observed if the conditions are right for constructive interference. If d is the distance between planes, reflected x-rays are only observed under these conditions: That's known as Bragg's law. The important thing to notice is that the angles at which you see reflected x-rays are related to the spacing between planes of atoms. By measuring the angles at which you see reflected x-rays, you can deduce the spacing between planes and determine the structure of the crystal....
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## This note was uploaded on 11/22/2011 for the course PHY PHY2053 taught by Professor Davidjudd during the Fall '10 term at Broward College.

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