Anharmonic Contributions to Elastic and Inelastic Scattering of X Rays at Bragg Reflections in Aluminum

The scattering intensities of the 14.4-KeV $\gamma$ rays from ${\mathrm{Co}}^{57}$ were measured at the {333} and {444} reflections of A1 crystals in the temperature range 295-800°K. The elastic and inelastic components of the scattered intensities were separated by means of the Mössbauer effect. The temperature dependences of the integrated intensities of the elastic peaks give evidence of non-Gaussian anharmonic contributions to the Debye-Waller factors. Comparison is also made between experimental and calculated temperature dependences of the inelastic intensities. Some of the discrepancies found at the {444} reflection are explained by admitting a non-neglectable contribution of non-Gaussian terms in the correlation part of the formula for the intensity of the thermal diffuse scattering.