Detachable and robust three-dimensionally printed support structures for optical coupling of lightguide to photomultiplier tube

This study introduces a novel optical coupling structure for scintillation detectors, which are critical tools in high-energy physics, nuclear engineering, medical physics, and radiation applications. The proposed design focuses on optimizing optical coupling efficiency, mechanical strength, stability, and maintainability between a light guide and a photomultiplier tube (PMT), particularly for large-area scintillators. Accordingly, a customized support structure was fabricated using fused deposition modeling to precisely align and secure the light guide and PMT. A fabricated structure using carbon-fiber-reinforced polyethylene terephthalate glycol filament was equipped with an interlocking mechanism enabling easy assembly and disassembly. To assess the long-term performance and stability of different optical coupling techniques, we evaluated the effects of reactor neutrino exposure and environmental conditions on optical transmittance. Specifically, ultraviolet‒visible spectroscopy was performed on optical cement exposed to a reactor neutrino exposure environment for 12 years, revealing a decline in optical performance likely due to oxidation, decomposition, and the formation of color centers or defects. Additionally, the transmittance spectra of optical grease and cement cured under controlled temperature and humidity were compared. Finally, the impact of an air gap between the light guide and PMT, caused by insufficient optical grease application, on the cosmic ray background charge distribution was analyzed. In the future, this study could contribute to improving the better optical coupling structure between light guide and PMT for the development of radiation measurement technology.