Dispersion des vitesses des ondes acoustiques dans l'aluminium

Intensity measurements of X-ray diffuse scattering by single crystals of aluminium at ordinary temperatures give information on the mode of propagation of transverse and longitudinal elastic waves in the crystal. Using monochromatic radiation each intensity (measured by an ionization chamber) can be expressed in terms of an average total scattering power (including Compton scattering) which has to be corrected (a) by a divergence factor corresponding to the resolving power of the spectrometer; (b) for the Compton effect associated with an atom-forming part of a crystal; (c) for second and third order scattering due to simultaneous scattering on two or three acoustic waves; and (d) for the true quantized energy distribution among the acoustic waves. From these results the phase velocities of longitudinal and transverse elastic waves in aluminium are obtained as functions of the elastic wave vector S = 1/[Lambda]. For very small values of S (long acoustic waves) the velocities found correspond to those quoted in the literature for static measurements. Otherwise a remarkable curve of dispersion, v= f (S), is established for the elastic waves, which for transverse waves makes f (S) very nearly a sine function such as would be expected if only the twelve nearest neighbours about each atom interacted with it. For longitudinal waves this is definitely not the case.