addBeam(obj, beam)
  addBeam(obj, beam, fDelta, fTheta, fPhi)
 
  addBeam(obj, beam, fDelta, fTheta, fPhi)
   fDelta, fTheta, fPhi are the angles between the beam
   propagation direction and the crystal orientation (the 
   definition of beam direction in crystal frame of reference).
   Use this instead of defining an absolut material orientation 
   with respect to the simulation coords. You'll have to call 
   this for one beam only (only once).
 
  addBeam(obj, beam)
   use this to define all other beams, or if material
   orientation is already set through addMaterial