Letter | Published:

X-Ray Scattering by Thermal Vibrations in Crystals

Nature volume 162, page 216 (07 August 1948) | Download Citation



SIR C. V. RAMAN, in his letter on "X-Rays and the Eigen-Vibrations of Crystal Structure"1, claims that the elastic vibrations cannot "give rise to any geometric diffraction pattern exhibiting an observable relationship to the structure of the crystal". The reasons given for this statement make it appear that he has fallen into Debye‘s original error, and supposes that the atomic vibrations are essentially independent, or are markedly dependent on the form of the crystal and on external boundary conditions. This would perhaps be the case for very small crystallites ; for crystals of ordinary size the boundary conditions would involve second-order effects only, as they do in the case of Bragg reflexion. It should also be clearly understood that the change of frequency due to the X-ray ‘Doppler effect' is so small that the modified wave-lengths still lie well within the width of the monochromatized Kα1 line, assuming that to be the incident radiation ; the change is of the order of 1 in 105.

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  1. 1.

    , Nature, 162, 23 (1948).

  2. 2.

    , Proc. Roy. Soc., A, 179, 320 (1942). , and , Nature, 148, 628 (1941); 149, 21 (1942). , Proc. Phys. Soc., 64, 314 (1942).

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  1. University College, Gower Street, London, W.C.1. July 15.



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