Slow Scintillation Component and Radiation-Induced Readout Noise in Undoped CsI Crystals

Because of its fast scintillation and low cost, undoped CsI crystal has been used to construct crystal calorimeters for high-energy physics experiments. Undoped CsI crystal samples from three vendors were investigated at the Caltech Crystal Laboratory. In addition to the 30-ns fast scintillation peaked at 310 nm, a slow scintillation component peaked at 450 nm was found with a decay time of a few microseconds. The intensity of the slow component may be varied from the seed to the tail end, so it affects crystal's light response uniformity. It was also found that the slow component is highly correlated with the radiation-induced readout noise and may be eliminated spectroscopically by using an optical filter. The slow component is believed to be related to impurities and/or defects in the crystal.