A gamma photon detector for detecting 511 keV PET radiation includes a scintillator host material doped with cerium. The cerium is present in a concentration of 0.1 to 1.0 mol %. Lower concentrations increase light output but also decay times which can lead to pile up issues. The higher light output enables the read out area to be decreased which reduces the pile up issues. Embodiments with a cerium concentration as low as 0.15 to 0.2 mol % and a read out area as low as 0.1 cm2 are contemplated.