A prototype scintillating fibre tracker for the cosmic-ray muon tomography of legacy nuclear waste containers

Tomographic imaging techniques using the Coulomb scattering of cosmic-ray muons are increasingly being exploited for the non-destructive assay of shielded containers in a wide range of applications. One such application is the characterisation of legacy nuclear waste materials stored within industrial containers. The design, assembly and performance of a prototype muon tomography system developed for this purpose are detailed in this thesis. This muon tracker consists of two tracking modules above and below the volume to be assayed. Each module comprises two orthogonal planes of 2mm fibres. The modular configuration allows the reconstruction of the initial and scattered muon trajectories which enable the container content, with respect to atomic number Z, to be determined. Fibre signals are read out by Hamamatsu H8500 MAPMTs with two fibres coupled to each pixel via dedicated pairing schemes developed to avoid space point ambiguities and retain the high spatial resolution of the fibres. The design, component tests and assembly of the detector system are detailed and presented alongside results from commissioning and performance studies with data collected after construction. These results reveal high stability during extended collection periods with detection efficiencies in the region of 80% per layer. Minor misalignments of millimetre order have been identified and corrected in software. A GEANT4 simulation was created and used for testing image reconstruction algorithms and for comparison to experimental scenario. A likelihood-based image reconstruction algorithm was developed and is described with reconstructed image results from simulated and experimental data for various scenarios are presented. These results verify the simulation and show discrimination between the low, medium and high-Z materials imaged and highlight the high spatial resolution provided by the detector system