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X-ray Analyses of Proteins and Nucleic Acids /1 5 : 4 



Another type of diffraction pattern, called a Laue pattern, avoids this 

 problem by using heterochromatic X rays of many wavelengths incident 



Figure 5. Laue pattern of NaCl. This has been redrawn 

 from a photograph to emphasize the diffraction spots. The 

 Miller indices of the corresponding planes have been labeled 

 for some of the diffraction spots. 



Crystal Plane 

 82 



d sin 6 



Crystal Plane 

 ttl 



Ray reflected at 2nd plane has 

 traveled 2d sin 9 further than ray 

 reflected at first plane 



Incident 

 X -ray Beam 



Diffracted 

 X -ray Beam 



Figure 6. X-ray diffraction. The dotted lines show perpen- 

 diculars to the wavefront. For re-enforcement, the rays 

 reflected at planes 1 and 2 must travel distances which differ 

 by a whole number of wavelengths. This will be fulfilled if 



nX = 2d sin 6 



where n is an integer. 



in a fixed direction. However, because A will not be known, one cannot 

 find the distance between reflecting planes from a Laue pattern. 





