Effect of atomic size on the minimum X-ray absorption coefficient in the six-beam Borrmann diffraction

The effect of the finite size of atomic electron shells on the minimum X-ray absorption of the six-beam (0 0 0, 2 2 0, 2 4 2, 0 4 4, 2 2 4, 2 0 2) Borrmann diffraction is discussed. An X-ray wave field calculation shows that the minimum photoelectric absorption in Ge by the L electrons located at a distance of r = 0.086 A ̊ from the centres of the atoms is about 2 cm-1, one hundred times higher than the absorption coefficient of 0.02 cm-1 at r = 0. We explain the absorption of the six-beam Borrmann diffraction observed experimentally using this result. Our analysis also predicts that the multiple-beam Borrmann effects should be less observable in Si and in diamond. © 1990.