bragg's law...tabish ansari


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English physicists Sir W.H. Bragg and his son Sir W.L Bragg in 1913... carefully planed a technique for the study of diffraction of X-rays by considering the scattering of X-Rays by the atoms in the crystal lattice… that is known as…

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Bragg ‘s Law

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Ray diagram of Bragg’s law

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A narrow beam of monochromatic X-Ray of wavelength( λ ) be incident on planes in crystal at a glancing angle ( Θ ) These rays are scattered by the atom like B and B’ of two adjacent planes of separation ‘d’.

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The following condition to verify the Bragg’s Law- 1. Angle of incident = Angle of scattering 2. The path difference is equal to an integral multiple of wave length. i.e n λ = 2 d sin Θ


Construction Here BM and BN are perpendicular drawn from B. then the path difference b/w A and A’ is equal to… MB‘ + B’N

Path Difference:

Path Difference Path diff. = MB’ + B’N = d sin Θ + d sin Θ = 2d sin Θ for constructive pattern, the path diff. is integral multiple of wavelength ( λ ) i.e 2d sin Θ = n λ

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Daigram of Bragg’s spectrometer

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Much of our knowledge about crystal structure and the structure of molecules as complex as DNA in crystalline form comes from the use of x-rays in x-ray diffraction studies.

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A basic instrument for such study is the Bragg spectrometer .

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To obtain nearly monochromatic x-rays, an x-ray tube is used to produce characteristic x-rays . matched filters are used in the x-ray beam to optimize the fraction of the energy. WORKING

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Such filters use elements just above and just below the metal in the x-ray target, making use of the strong "absorption edges" just above and below the K-alpha energy of the target metal.

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The x-rays are collimated with apertures in a strong x-ray absorber and the narrow resulting x-ray beam is allowed to strike the crystal to be studied.

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The spectrometer arrangement couples the rotation of the crystal with the rotation of the detector so that the angle of rotation of the detector is twice that of the crystal.

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This satisfies the conditions of Bragg's law for diffraction of the x-rays from the crystal lattice planes.



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The first Spectrometer

Another rays diagram spectrometer:

Another rays diagram spectrometer

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bye bye & thanks to all of you

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