Bragg's Law and the Laue equations predict diffraction at
only precise Bragg angles for an infinite crystal. Many diffraction experiments
(especially in transmission) are carried out on specimens which are thin in at least one
dimension.
Try changing the size of
the crystal above by dragging the top white left-hand corner of the crystal.
Notice the corresponding change in the reciprocal lattice points.
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The effect of small dimensions is to allow diffraction
over a range of angles close to the Bragg angle. This has
the same effect as if the relative reciprocal lattice
points (relpoints) were stretched out in the direction
of thinness of the sample. The streaked reciprocal lattice
points are now called relrods.
Is the following statement about relrods true?
The length of each relrod is proportional to the thickness of the crystal in
that direction.