What is Afterglow?

To detect fast changes in transmitted intensity of X-Ray beams, such as in CT scanners or luggage X-ray detectors, crystals are required exhibiting low afterglow. Afterglow is defined as the fraction of scintillation light still present for a certain time after the X-Ray excitation stops. Afterglow originates within a millisecond and can last hours in long decay time components. Afterglow in most halide scintillation crystals can be as high as a 5-10 percent after 3 ms. The long duration afterglow in e.g. CsI(Tl) can be a problem for many applications. Afterglow in halides is believed to be intrinsic and correlated to certain lattice defects. BGO, CeBr3, and Cadmium Tungstate (CdWO4) crystals are examples of low afterglow scintillation materials.