Issue with Optical Photon Detection in PPAC Simulation

[hkumi]

Hello everyone,

I am working on a Geant4 simulation to design a Parallel Plate Avalanche Counter (PPAC) intended for optical photon detection. In my geometry, I have configured two thin electrodes for electron drift, along with an array of collimators and silicon photo sensors that are supposed to detect optical photons.

While I can visually observe optical photons in the simulation, my sensors only register neutrons and gamma rays. I’ve included code to print the type of particle hitting the sensors, and no optical photons are detected.

In my detector construction, I defined the optical parameters (such as refractive index and other relevant properties) for most materials, but I realize I did not specify any optical parameters directly for the silicon sensor itself. Could this omission be preventing the sensors from detecting optical photons? If so, could someone guide me on how to correctly configure the sensors for optical photon sensitivity?

I’ve attached my simulation files and the output I’m currently receiving. Any insights or suggestions on how to resolve this would be greatly appreciated.

Thank you all in advance for your help!

detector.cc (3.6 KB)
DC.cc (55.3 KB)

_Geant4 Version: geant4-v11.1.3
_Operating System: Ubuntu 22.04.5 LTS
_CMake Version: VERSION 3.0 FATAL_ERROR

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[Keith-Huddleston]

I think you are correct, not assigning an index of refraction to the detector volume is likely the issue. If I remember right when no index of refraction is defined for a volume the photons are killed at the surface and hence never enter the detector volume. A quick solution would be to assign an index of refraction to the volume the detector is assigned to, the value of the index of refraction should be equal to the surrounding media so no reflection or refraction would occur.

[hkumi]

Thank you very much for your responds. Indeed it was because of the omission. its working now. Thank you