Monte Carlo Simulation of Propagation of Optical Photons in ICARUS Cosmic Ray Tagger Scintillation Units

Propagation of optical photons in ICARUS cosmic ray tagger (CRT) system is simulated using FLUKA, a Monte Carlo simulation software. Variation of the signal with respect to the position of incident cosmic ray muon is studied. A transverse scan of the scintillation unit shows the variation in the number of optical photons detected by the SiPM detector. A longitudinal scan measures the effective photon propagation rate to be 6.17ns/m. These values precisely agree with experimental measurements of the CRT prototype. Moreover, the effect on the signal waveform by defective TiO2 reflective coatings is studied. It is shown that the reflectivity of TiO2 paint plays a significant role in retaining the optical photons inside the CRT module.