Caf:Eu
Calcium fluoride activated by europium is a light scintillator used in detection of charged particles and soft gamma rays up to several hundreds keV. CaF:Eu is typically used for the detection of beta rays due to its relatively small back scattering. It is not suitable for detection of high-energy gamma rays because it has a small photofraction. The material is not hygroscopic and is relatively chemically inert.
For more information see Scintillation material data