Optical Photons leaving end of Scintillator Bar too small?

Hello Again,

so I have a scintillator bar with specified dimensions 5x10x75 cm(75 cm long). I am shooting muon beam right ( 1 GeV Kinetic energy) at the center of the scintillator bar cross-section (5x10). I have also placed a sensitive detector at the end of one of the scintillator bar with specified properties which I adapted from OpticalNovic examples. The scintillator bar is NOT currently wrapped.

I believe I have correctly implemented optical properties.

And my sensitive volume is placed right after the scintillator bar and I Believe I implemented the sensitive detector correctly, however I noticed that most of optical photons escaped at the front edges of bar. Is this intended effect ?

In the image below I have placed a separate sensitive detector away from bar slightly for visual imaging.

For instance, the number of scintillation photons produced by bar is roughly 600,000 while I get number of optical photons exiting the scintillator bar into sensitive detector to be more or less around 70,000. Is this number reasonable or too small (a reference would also help) ?

First of all, there is a well known issue with optical photons leaving corners of volumes

See Figure 4 in this paper.

For the number of photons detected in your detector, that depends on:

  • Absorption length of your scintillator
  • Index of refraction of your scintillator vs index of refraction of the volume it lays in
  • Reflectivity (but you say it is not wrapped, so reflectivity will only depend on index difference and angle

Probably @loydms is correct and that it is due to the indices of refraction. You could investigate by visualizing one optical photon at a time (it’s hard to see what’s going on in the figure). I don’t know how to do that in visualization. You could find where the photon is created, its direction and energy, and use that as a primary. Or reduce the scintillation yield until only a few photons are produced.

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Hi, thanks for the feedback I am quite familiar with the paper. Has the issue with optical photons leaving corners been resolved in recent GEANT4 editions?