Fig. 1

Total number of photons detected per gamma event for different detectors and surface finishes, assuming an SiPM photon detection efficiency of 50%. Both detector surfaces are coupled to the SiPM array by optical grease (refractive index = 1.5). The side surfaces are a polished surface coupled with optical grease to a specular reflector (PolishedESRGrease), a rough surface coated with black paint (RoughBlack) and a rough surface with no coating (Rough). The top surface is always PolishedESRGrease.