X-ray Diffraction

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X-ray Diffraction

X rays can be defined as “electromagnetic waves of short wavelength,

capable of penetrating some thickness of matter.” Approximately the

same size as an atom, the wavelength of an X-ray is about 1 Ã… (10-10m).

They occur in the portion of the electromagnetic spectrum between

gamma rays and ultra violet light and have proved very useful in

determining crystal structures since their discovery on November 8th,

1895.

German scientist Wilhelm Roentgen was conducting experiments in his

laboratory on the effects of cathode rays. Specifically he was

observing the effect of passing an electrical charge through gases at

a low pressure. While doing so, Roentgen noticed something that

earlier studies had not picked up. While passing current through the

cathode ray, other rays were being given off that passed through all

everyday matter such as wood, aluminium and paper. Roentgen further

observed a surface he had coated with barium Platinocyanide that was

placed outside of the cathode discharge tube would still emit light,

despite the fact that it was concealed from the light of the

discharge. The conclusions that Roentgen came to were that a new type

of radiation had passed through the air and lit up the screen

(X-rays).

Due to this discovery in 1895, scientists were able to probe

crystalline structures at an atomic level. X-ray diffraction has been

in use in two main areas; for the finger print characterization of

crystalline materials and the determination of their structure. Each

crystalline solid has its unique X-ray powder pattern which may be

used as a clue for its identification. Once the material has been

identified, X-ray crystallography may be used to determine its

structure, for instance how the atoms pack together in a crystalline

state and what the distance and angle between the atoms are. We can

determine the size and shape of a unit cell for any compound most

easily using the diffraction of x-rays.

X-ray diffraction is the scattering of x-rays by crystal atoms,

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