X-Ray Diffraction

X-Ray powder DiffractionMustafa AL-doori

Mustafa aldorri1

THE MAIN AXES:1- Introduction 2-Bragg's Law3-Prove Bragg's Law4-Generating x-ray5- x-ray tube6- Debye Scherrer camera7-X-ray Diffractometer8-Conclusion

Introduction X-Rays are electromagnetic radiations with wave lengths of the order of 0.1nm.

X-rays are produced when electrons from a heated filament strike the metal target.

In 1912 physicist Max Von Laue discovered that a crystalline solid , consisting as it does of regular array of atoms ,might form a natural three - dimensional diffraction grating for x-rays.

Question:So if all electromagnetic radiation can diffract, why are X-rays used in crystallography?Ans.X-rays have wavelengths on the order of a few angstroms (1 Angstrom = 0.1nm). This is the typical inter-atomic distance in crystalline solids, making X-rays the correct order of magnitude for diffraction of atoms of crystalline materials.

Introduction A grating with d= wavelength is desirable for x-ray diffraction.

diffraction occurs when a wave encounters a series of regularly spaced obstacles that are;

Capable of scattering the wave.

Have spacing that are comparable in magnitude to the wavelength

Braggs law In 1914 W.H Bragg and W.L Bragg study the atomic structure of crystal by using X-rays Consider the two parallel planes of atoms A-A And B-B which are separated by interplanar spacing d.Now assume that a parallel , monochromatic beam of x-rays of wavelength is incident on these two planes at an angle . two rays in this beam , labeled 1 and 2 are scattered by atoms P and Q.

ray 2 covered some extra path as compared to ray 1 this extra path is called path difference .Constructive interference of scattered rays 1 and 2 at an angle to the plane, if the path difference between 1- P-1 and 2-Q-2 ,is equal to whole number , n , of wavelength; so

It will prove Bragg's Law

There will be a path difference between theraythat gets reflected alongAC'and the ray that gets transmitted, then reflected, alongABandBCrespectively. This path difference is

The two separate waves will arrive at a point with the samephase, and hence undergoconstructive interference, if and only if this path difference is equal to any integer value of thewavelength, i.e.

where the same definition of and apply as above.Therefore,

from which it follows that

Putting everything together,

which simplifies to

Generating x-ray

X-ray tube

Debye Scherrer camera:

A very small amount of powdered material is sealed into a fine capillary tube made from glass that does not diffract x-rays. The specimen is placed in theDebyeScherrercamera and is accurately aligned to be in the centre of the camera. X-rays enter the camera through a collimator.The powder diffracts the x-rays in accordance with Braggs law to produce cones of diffracted beams. These cones intersect a strip of photographic film located in the cylindrical camera to produce a characteristic set of arcs on the film.

X-ray Diffractometer

Some images x-ray

ConclusionX-ray diffraction is important for :

1- solid-state physics2- biophysics 3- medical physics4- chemistry and biochemistry