Accurate Determination of Structure Factors by Pendellosung Methods Using White Radiation

This paper describes two experimental techniques measuring the Pendellosung beats using white radiation, developed in the authors' laboratory. The intensity of a Laue spot diffracted from a parallel-sided single crystal is successively measured at different Bragg angles, i.e. with different wavelengths. The values of structure factors are evaluated from extremum positions in the measured beats on the basis of the dynamical diffraction theory. In the first method, the integrated intensity diffracted from the whole exit surface is measured, and in the second, the measurement is made only at the centre of the Borrmann fan on the exit surface of a specimen. A discussion is given on the accuracy associated with the following origins of errors: (1) polarisation of incident white radiation, (2) measurement of specimen thickness, (3) measurement of wavelength, (4) determination of extremum positions, and (5) effect of defects in the crystal.

The effect of thermal vibrations on the scattering of X-rays. II

The theory of background scattering developed in Part I is worked out in detail. It is shown that only the acoustical branches of the elastic spectrum can produce extra spots. The temperature dependence of the background intensity is discussed. It is shown that the properties of an extra spot in the vicinity of a Laue spot can be derived from the elastic constants of the crystal, and explicit formulae for the position and shape of the spots are given for cubic crystals with diagonal lattices.