Organic and Inorganic Scintillation Detector Calibration and Optimization for Neutral Atom Trap

At TRIUMF's Neutral Atom Trap, we investigate the time-reversal symmetry in beta decays of trapped atoms. We look for the correlation of three momenta from beta-neutrino-gamma coincidences when a gamma is emitted from the radioactive nuclei that could indicate a violation of time-reversal symmetry. The decay products are detected with organic and inorganic scintillators with Si photomultiplier (SiPM) readouts. We report the calibration and optimization studies for a 35 mm-thick plastic and two GAGG (Gadolinium Aluminium Gallium Garnet) scintillators. We studied the effect of the increasing overvoltage bias on the gain, the photon detection efficiency, and the dark current. Several reflectors used for wrapping the detectors were compared in terms of the change in the energy resolution. Overall, an overbias voltage of 5.5 V with PTFE and ESR wrappings was found to improve the energy resolution. The average resolutions for the GAGG detectors were determined as 8.9% and 6.9% at 662 and 1333 keV gamma-ray photopeaks, while the resolution for the plastic scintillator was measured as 10-11% for IC electrons around 1 MeV. The coincidence timing resolution for the gamma-ray coincidences between the GAGG detectors was also determined as 6.1 ± 0.5 ns.