Position Reconstruction of Gamma-ray Interaction in Monolithic Scintillator Crystals

Abstract

The localisation of the interaction position of γ rays in scintillator detectors are of interest for different applications such as nuclear medicine, astronomy, fundamental physics experiments and nuclear security. For instance, the localisation of the interaction position of gamma rays in a detector can provide information about reconstructing the actual source position such as the one used in Compton cameras meant for nuclear security. The 3D scintillator detector described in this thesis consists of a 50.44×50.44×50.44 mm3 cubic CsI:Tl crystal coupled, for the first time, to six 8×8 SiPM arrays on all of the six faces of the crystal. 2D average and single light maps were generated to visualise the interaction positions. The measurements were also compared to Geant4 simulations and a simplistic geometrical model, and both showed a reasonable agreement with each other. The interaction position was successfully determined by using the light ratio method using both experimental and simulation data. Covering all of the six sides of the detector simplified the localisation and the 3D position reconstruction of the rays interaction inside the detector. All of the three coordinates were reconstructed using the χ 2 minimisation that uses the estimation based on the data of the simplistic model. The position resolution was measured at the edges and the central region of the detectors using the reconstructed data obtained from both these methods. At the edges, the resolution was found to be 1.4 mm and 2.6 mm, whereas in the central region, it was calculated to be 2.3 mm and 3.7 mm for the χ 2 minimisation and the light-sharing method respectively. The results obtained are exciting, and the interaction positions can be reconstructed using the light-sharing measurements obtained from all of the six arrays. Moreover, the position resolution can be quantified by using the reconstructed events light distribution