Growth and optimization of the scintillation properties of Gd₃(Ga,Al)₅O₁₂ single crystals for WGI applications

A new scintillator was developed as a scatterer for whole gamma imaging (WGI). The WGI scatterer is required to meet simultaneously three main characteristics: energy resolution of 5.5 % or less, light yield of 40,000 photons/MeV or greater, and a decay time of 100 ns or shorter. Several scintillators were selected and evaluated from previously grown single crystals, leading to the selection of a candidate scintillator crystal as the basis for optimization, with energy resolution being the primary focus. Based on the selected crystal composition, large single crystals were grown via the Czochralski method. The Ga/Al ratio in the GAGG-type host crystal, along with the Mg co-doping concentration, was systematically adjusted to achieve optimal properties. The optimized crystal exhibited scintillation properties with an energy resolution of 5.28 % at 662 keV, a light yield of 45,200 photons/MeV, and a decay time of 92 ns. After evaluating their characteristics by manufacturing them in a 4 × 4 array, the single crystals used in the production of a full-block array (14 × 14) for the scatterers were finally selected. Subsequently, the crystals were employed to construct a full-block array, which demonstrated energy resolution nearly identical to that of the 4 × 4 array. No observable performance degradation was evident even in the larger array configuration. These array blocks, produced using the optimized crystals, are being tested by applying them to a WGI prototype system at the National Institutes for Quantum Science and Technology in Chiba, Japan.