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Good day,

This is my first time simulating optical photons, so please bear with my ignorance. Iā€™m trying to simulate a plastic scintillator and a photo-sensor at both end of the plastic wrapped with PTFE reflector. I have read about boundary surfaces in the Book for Application Developers to understand the right model to adopt. In principle, there will be some air gap between the plastic and the PTFE. Below is the boundary surface I have defined in my code:

Plastic to PTFE:

Plastic to sensor:

My questions goes as follows:

  1. Is it correct to assume that the geometry tolerance in Geant4 between the plastic and the wrapper can serve as the air gap? Or do I need to define a thin layer of air between the two materials?

  2. What happens if I dont include other constant such as SPECULARSPIKECONSTANT?

  3. Using the above models, why is there no reflection and refraction but only absorption? See the attached figure.

Thank you.