A scintillator is a type of material that emits light when it is excited by an ionizing radiation. By “material”, I really mean “molecule”. Scintillators come in all forms: solid (usually crystalline), liquid and even gaseous. They are especially good at detecting electrons, gammas and neutrons. I will not enter into more details here, there are excellent industry blogs dedicated to the topic.
Beyond this general definition, there is a whole, fascinating universe of physical and chemical engineering in order to optimize a scintillator. But why is this optimization needed? Because as usual in life, nothing can ever be perfect. An ideal scintillator would be very dense in order to detect the elusive gammas, but transparent to the emitted light so that the photons can escape and be detected. In fact, transparency would only be a minimal requirement, because we would want the scintillator to emit as many photons as possible. And finally, it would be fast for a quasi-instantaneous detection.
While all this isn’t possible in one single material, material engineers have created different types of scintillators that can cater almost perfectly to specific applications.
However, a light-emitting material on its own is very nice… but not useful at all. Once again, we need to make a detector out of a sensor. In this case, we do so by coupling a scintillator with a light sensor. The light sensor must match the scintillator in terms of wavelength and speed, among others, and will output an electrical signal that will then pass into a data acquisition system and will be interpreted.
Applications of scintillators are incredibly vast: in physics research, neutrino experiments such as SNO+ use liquid scintillator as their main medium. Their sensitivity to gammas and neutrons also make them useful in security or medical applications. In fact, the scintillation field of activity is so big that it has its own biennal conference.