Worse, the thicker the material, the lower the resolution of the images produced by the scintillator detector. Light output or brightness is a second critical quality. Derenzo and Moses are looking for materials that are relatively efficient at transforming ionizing energy into photons. The most efficient known inorganic scintillator, sodium iodide, emits 10 percent of the ionizing energy as light. Bismuth germanate, the material most commonly used to create PET scans, has an efficiency of only two percent.
Some materials are faster light-emitters than others.
Generally, the shorter the time between the arrival of incoming gamma rays and the resultant flash, the less blurry the image.