Zur Absorption der Ewaldwellen; Messungen bei simultaner Reflexion an (111) und ([unk]11) des Germaniums

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Abstract
The paper deals with anomalous transmission (Borrmann effect). The least-absorbable Ewald wave, arising in a perfect crystal under the condition of Braggs law, exceeds the stronger absorbed waves more and more with the growing thickness of the crystal. As a matter of fact, the absorption coefficient μ ( t ) at the depth t decreases with increasing t . μ ( t ) tends towards the minimum absorption coefficient μ min but cannot reach it at a finite thickness. This was proved in the case of simultaneous reflection of x-rays by the (111) and ([unk]11) lattice planes of a Ge crystal, when μ min was expected to be extremely low ( μ min = 0.053 μ with λ = 1.54 Å, and only 0.022 μ with λ = 0.71 Å; μ normal absorption coefficient). According to theory the three waves of this least-absorbed Ewald wave have the intensity ratio of 2:1:1. The observed three reflections had the strength ratio of 2. 3 :1:1 ( λ = 1,54 Å) and 2. 15 :1:1 ( λ = 0.71 Å).

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