Evaluation of advanced methods and materials for construction of scintillation detector light guides

New techniques for fabrication of optically clear structures (3D printing and casting) can be applied to fabrication of light guides, especially complex -shaped ones, for scintillation detectors. In this investigation, we explored the spectral transmissivity of sample light guides created with different fabrication methods and materials. A spectrophotometer was used to measure the transmissivity of the samples to determine their compatibility with a number of commonly used inorganic scintillators (NaI(Tl), BGO, LaBr₃, LaCr₃, CSI(Tl) and LYSO). These measurements showed that stereolithography with a Stratasys 3D printer using Somos WaterClear Ultra 10122® produced the most compatible light guide with common organic scintillators, especially LYSO (peak emission λ=420 nm) (a scintillator commonly used in positron emission tomography (PET) imaging). Additionally, Polytek Poly-Optic® 1730 clear urethane produced a cast light guide that was the most optically compatible with these scintillators. To demonstrate the ability to create a unique shaped scintillation detector using 3D-printing and casting methods, a small arc-shaped piece of LYSO was coupled to a 4 × 4 array of 4 mm² silicon photomultipliers (SiPM) using light guides made from these materials. For comparative purposes, a light guide was also fabricated using standard acrylic, a material often used in current light guides. All detectors produced similar event position maps. The energy resolution for ¹⁸F (511 keV photopeak) was 13% for the acrylic light-guide-based detector, while it was 18% for the printed light-guide-based detector and 20% for the cast light-guide-based detector. Results from this study demonstrate that advanced fabrication methods have the potential to facilitate creation of light guides for scintillation detectors. Continued advancements in materials and methods will likely result in improved optical performance for 3D-printed structures.