A Study of Energy Resolution and Non-proportionality of YAlO3:Ce and Gd3Ga3Al2O12:Ce

For many radiation detection applications, energy resolution is one of the most important detector characteristics. In well designed scintillation detectors, the energy resolution is primarily driven by two main factors - the light output and light yield non-proportionality. A great deal of research has already focused on understanding and improving the light yield of scintillation detectors; however, light yield non-proportionality is less well understood. Until recently, light yield non-proportionality was thought to be an intrinsic scintillator property with very little sample-to-sample variation. In this work, two materials have been investigated that demonstrate a variable light yield non-proportionality. The first material investigated was Gd3Ga3Al2O12:Ce. For this material, it was determined that co-doping led to an observable change in light yield non-proportionality and light output, which in turn led to an improvement from 9.0% to 7.8% as a result of boron co-doping and a degradation to 10.1% as a result of calcium co-doping. The second scintillator investigated was YAlO3:Ce (YAP:Ce). This material was investigated because it is one of the few materials which exhibits a large sample-to-sample variation of light yield non-proportionality without intentional co-doping. Some of the best samples display a nearly ideal light yield non-proportionality and have an energy resolution as good as 4.3%, while some of the less optimal samples have an energy resolution as poor as 9% as a result of reduced light output, worsened proportionality, and a detrimental optical absorption band. Based on experimental evidence, it was determined that growth in a reducing atmosphere can suppress the detrimental optical absorption band and improve the light output. In addition, it was found that the Ce 3+ concentration was a key parameter in influencing the variable non-proportional behavior. Samples with a higher Ce 3+ concentration exhibited favorable proportionality, and it seems likely that the behavior can be explained by activator saturation.