Geant4 color code:  
green = photon (optical as well as gammas)
red   = negative charged particle (here: electron)
blue  = positive charged particle (if exists: positron)

1st pic: the cerenkov cone created inside the bar (wire frame side view)
         At the border you can see cerenkov photons escaping into air.
         I set an artificial high value for the air absorption length for optical photons,
         that is why they reach only ~1mm into the air. Otherwise the pics would be flooded
         with escaped cerenkov photons.  

2nd pic: shows the green cerenkov photons escaping the solid detector

3rd pic: shows the far end, only a few cerenkov photons will make it there (wire frame)

4th pic: shows the hole cerenkov detector (wire frame)


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