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

An energy resolution of 4.38+-0.11% was obtained for 662 keV gamma-rays with a 3x3x20 mm³ 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 withing +-2%. These observations are consistent with the assumption that there is a direct correlation between energy resolution of scintillators and nonproportionality of their light output versus energy.