Module Tester for Positron Emission Tomography and Particle Physics

The combination of high-density, high-time-resolution inorganic scintillation crystals such as Lutetium Yttrium Oxyorthosilicate (LYSO), Yttrium Orthosilicate (YSO) and Bismuth Germanate (BGO) with Silicon Photomultiplier (SiPM) sensors is widely employed in medical imaging, particularly in Positron Emission Tomography (PET), as well as in modern particle physics detectors for precisely timing sub-detectors and calorimeters. During the assembly of each module, following individual component testing, the crystals and SiPMs are bonded together using optical glue and enclosed in a light-tight, temperature-controlled cooling box. After integration with the readout electronics, the bonding is initially tested. The final readout electronics typically comprise Application-Specific Integrated Circuits (ASICs) or low-power Analog-to-Digital Converters (ADCs) and amplifiers, designed not to heat up the temperature-sensitive SiPM sensors. However, these setups are not optimal for testing the optical bonding. Specific setups were developed to test the LYSO + SiPM modules that are already bonded but not enclosed in a box. Through large data collection, small deviations in bonding can be detected if the SiPMs and LYSOs have been thoroughly tested before our measurement. The Monte Carlo simulations we used to study how parameters—which are difficult to measure in the laboratory (LYSO absorption length, refractive index of the coating)—affect the final result. Our setups for particle physics and PET applications are already in use by research institutes and industrial partners.