Intensity Attenuation and Enhancement in 3-beam Diffraction *

Borrmann and Hartwag [1] have shown that the anomalously high transmission of x-rays through perfect crystals in 2-beam diffraction is further enhanced when a third set of planes is brought to its diffracting position. Simultaneous 3-beam diffraction then takes place. That discovery has stimulated large numbers of investigations, in many of which major emphasis has been placed on the spectacular decreases of absorption which often accompany the onset of 3-beam diffraction [2], Relatively little attention has been paid to the equally significant attenuation of the diffracted intensity which often occurs in 3-beam diffraction and which may result in partial or total eclipse of the anomalous transmission [3]. Observation of these effects requires the use of relatively high resolution techniques [4], which may explain, in part at least, why they have been treated either sketchily or not at all, in the past. In this paper we discuss these and other factors which influence 3-beam intensities. Four photographs of 3-beam cases in germanium are used to illustrate the 3-beam effects. All three diffracted beams are recorded on each photograph. The enhancements and attenuations of the diffracted intensities will be analyzed qualitatively on the basis of simplified versions of 2 and 3-beam dispersion surfaces.