BRAGG’S LAW Presented By MD NURUDDIN RUPESH KR SHAH SHARDA UNIVERSITY
BRAGG’S LAW Braggs law gives the angles for coherent and incoherent scattering from a crystal lattice. When X-rays are incident on an atom, they make the electronic cloudmove as does any electromagnetic wave. The movement of these charges re- radiates waves with the same frequency this phenomenon is known as Rayleigh scattering (or elastic scattering).
A similar process occurs upon scattering neutron waves from the nuclei. These re-emitted wave fields interfere with each other either constructively or destructively producing a diffraction pattern on a detector or film. The resulting wave interference pattern is the basis of diffraction analysis. This analysis is called Bragg diffraction.
Bragg diffraction (also referred to as the Braggformulation of X-ray diffraction) was firstproposed by William Lawrence Bragg and WilliamHenry Braggin 1913 in response to their discoverythat crystalline solids produced surprising patternsof reflected X-rays.The concept of Braggdiffraction applies equally to neutrondiffraction and electron diffraction processes.
W. L. Bragg explained this result by modeling the crystal as a set of discrete parallel planes separated by a constant parameter d. It was proposed that the incident X-ray radiation would produce a Bragg peak if their reflections off the various planes interfered constructively. The interference is constructive when the phase shift is a multiple of 2π;
So Bragg’s law given as Where n is an integer, Lambda is a wavelength of incident wave, d is the space between the plane in atomic lattice, is the angle between incident ray and the scattering plane.
Braggs Law was derived by physicist Sir William Lawrence Bragg in 1912 and first presented on 11 November 1912 to theCambridge Philosophical Society. Although simple, Braggs law confirmed the existence of real particles at the atomic scale, as well as providing a powerful new tool for studying crystals in the form of X-ray and neutron diffraction.
William Lawrence Bragg and his father, Sir William Henry Bragg, were awarded the Nobel Prize in physics in 1915 for their work in determining crystal structures beginning with NaCl, ZnS, and diamond.
Bragg diffraction occurs when electromagnetic radiation or subatomic particle waves with wavelength comparable to atomic spacings are incident upon a crystalline sample, are scattered in a specular fashion by the atoms in the system, and undergo constructive interference in accordance to Braggs law. For a crystalline solid, the waves are scattered from lattice planes separated by the interplanar distance d. Where the scattered waves interfere constructively, they remain in phase since the path length of each wave is equal to an integer multiple of the wavelength. The path difference between two waves undergoing constructive interference is given by 2dsinθ, where θ is the scattering angle. This leads to Braggs law, which describes the condition for constructive interference from successive crystallographic planes.