Digitizer-Based Single Photoelectron Detection Approach for Light Yield Measurement of Inorganic Scintillators

Background: Absolute light yield measurement based on single photoelectron (SPE) approach remain susceptible to random coincidences between pulsed excitation trigger and the photomultiplier tube (PMT) response. Few studies have reported a quantitative comparison of SPE-based light-yield estimation before and after random-coincidence suppression. To address this, we developed a simplified digitizer-based setup to quantify the light yield using a predefined time window to suppress random-coincidence events. Materials and Methods: SPE spectra were measured by stimulating a PMT with a dim light emitting diode, and the anode signals were recorded using a high-speed digitizer. Event time-stamps were used to select correlated signals within the time window. A 1˝×1˝ CsI(Tl) scintillator was sequentially coupled to R2228 and R1924A PMTs under identical configurations to verify the consistency of the measured light yield across the two PMTs. Results and Discussion: Suppressing random coincidences eliminated bias in SPE estimation, which otherwise led to an ~11% overestimation in light yield. The CsI(Tl) light yield was determined as 50,000±2,000 photons/MeV and 51,000±2,000 photons/MeV for R2228 and R1924A PMT, respectively. This digitizer-based SPE approach provides a reliable and reproducible method for light yield measurement. Conclusion: We demonstrated a simplified digitizer-based SPE measurement method, applying a time-window filter to reject random coincidence events. This approach enables accurate estimation of the SPE charge and, consequently, a reliable and reproducible light yield evaluation, which have been confirmed with consistent results obtained by the two PMTs.