Bragg's Law

Short Description of Topic

The Main Idea

Bragg's Law is a phenomenon in physics that relates the angles for coherent & incoherent scattering of crystal lattices, the wavelength of the incident wave, and the distance that the wave travels; the distance traveled by the wave depends on the separation of the layers and the angle at which the X-ray entered the material. This diffraction occurs when radiation, with wavelength comparable to atomic spacings, is scattered in a specular fashion by the atoms of a crystalline system, and undergoes constructive interference. The waves must interfere constructively in order for Bragg's Law to be valid. Also, the wave which reflected from the surface needs to have traveled a whole number of wavelengths while inside the material.

The path difference between two waves undergoing interference is given by 2dsinθ, where θ is the scattering angle. Bragg's Law ultimately describes the largest angle θ such that constructive interference is at its strongest.

A Mathematical Model

n is an integer describing the order of the reflection.

Bragg's law, as stated above, can be used to obtain the lattice spacing of a particular cubic system through the following relation:

where h, k, and l are the Miller indeces of the Bragg plane. Putting it all together we have:

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External links

[1]

References

http://www-outreach.phy.cam.ac.uk/camphy/xraydiffraction/xraydiffraction7_1.htm