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Geometry

  Streaking Reciprocal Lattice Points     15 of 18
 
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.

Have a go imageTry 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.

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.

Questions image Is the following statement about relrods true?

• The length of each relrod is proportional to the thickness of the crystal in that direction.

 

 
 

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