Optimisation and performance test of fibre-based large-area surface contamination monitor

Abstract A portable large-area radiological contamination surface monitor of advanced design is now under research and development. This monitor, whose detection area is 1200 cm2, is mainly applied for hot-spot searching for nuclear emergency response or facility decommissioning. It consists of a thin plastic scintillation tile and wavelength-shifting fibres coupled to a photomultiplier tube. To improve the detector performance, it is necessary to calculate the collection efficiency of optical photons from the scintillator. The optical photon transportation processes in the plastic scintillator and wavelength-shifting fibres are simulated using the Monte Carlo code Geant4. For further optimisation, experiments with different fibre arrangements are conducted to verify uniformity. In conclusion, an arrangement of ten neighbouring wavelength-shifting fibres, with alternating fibres connected on opposite sides of a organic support for the plastic scintillator presents a better performance for detection.