Geant4-GATE simulation of a large plastic scintillator for muon radiography

Envisaging the possibility of using large area plastic scintillator slabs as robust detectors for high spatial resolution muon radiography, and prior to prototype development, we study expected basic performance by Monte Carlo simulation. We present preliminary results for a scalable square footprint detector unit of ~1 m², defining a representative simulation model volume of 50 cm × 50 cm, with reflective surfaces and light readout by direct coupling of 4 small PMTs (in a square arrangement) at one face of the scintillator slab. Light detection efficiency is calculated for several light collection configurations, considering different values of surface roughness, reflectivity, optical coupling index and scintillator thickness. Values maximizing photon detection have been identified. The light response function (LRF) of photodetectors for the proposed configuration has been determined. An average spatial resolution of the order of 1 cm is expected to be achieved using statistical methods for interaction point determination (based on MC a priory information and maximum-likelihood estimation).