: a law in physics: there is a definite relationship between the angle at which a beam of X rays must fall on the parallel planes of atoms in a crystal in order that there be strong reflection, the wavelength of the X rays, and the distance between the crystal planes : sin Θ = nλ / 2d where Θ is the angle between the incident or the reflected beam and the crystal plane, λ is the X-ray wavelength, d is the crystal plane separation, and n is any integer                                      
                
                    
            
   
                   
             
                    
                        
        
        
        
                
                
                
        
                
     
    
                                                    
                                                                                                                    
            
                                    
                        
                                                    
                                
                       
                                        
                
                                                
                            
            
                                    
                                    
                        
                                            
                                                            
                                    
                                                                
                                
                                    
                
                
                
                
                
                
                
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
                                        
                                                    
                            
                                                               
                                                
  
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  Merriam-Webster unabridged
 
                          
                    
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