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[marius <marius@hexa.e17.physik.tu-muenchen.de>]

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> Can someone explain to me (in simple words) the pratical
> and theoretical usefullness of a diffractometer with kappa
> geometry with magic angle (54.? deg) using pre-oriented
> and randomly oriented crystals.

I have to be more specific:
Rotation of the crystal cuts a torus out of reciprocal space. 
Once one of the reciprocal cell axes is oriented along the rotation
axis some reflecions (or their symmetry mates) never pass
through the Ewald sphere. Hence, completeness is severly hampered.
I *believe* that the magic angle
inclines the crystal in an optimal way and makes shure that
an optimal number of unique reflections are collected.
Well, I am missing the theoretical background to prove this.
Therefore, I asked the question shown above. 
Help is very wellcome.

Marius 


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Dr. Marius Schmidt                        
Physikdepartment E17 
Technische Universitaet Muenchen
James Franck Strasse                
85748 Garching  
      Germany

Email: marius@hexa.e17.physik.tu-muenchen.de
Tel  : +49/89/2891-2550
Fax  : +49/89/2891-2548 
E17 im WWW: 
       http://www.physik.tu-muenchen.de/lehrstuehle/E17/bio_server.html
_____________________________________________________________________________