A high-energy resolution observed from a YAP : Ce scintillator

An energy resolution of 4.38±0.11% was obtained for 662 keV γ-rays with a 3×3×20 mm ³ YAP : Ce crystal with its long face coupled to an XP2020Q photomultiplier. The measured number of photoelectrons of 5290±80 phe/MeV implies a photoelectron statistical contribution of 4.18±0.04% and hence a YAP intrinsic energy resolution of 1.3±0.5%, the lowest value ever observed for scintillators. The relative light output of the YAP crystal measured for energies between 14.4 keV and 1.275 MeV was constant within ±2%. These observations are consistent with the assumption that there is a direct correlation between the energy resolution of scintillators and nonproportionality of their light output versus energy.