I’ve bought this 10x10x30mm CsI undoped crystal scintillator from Moscow. It’s looking great! Let we see what Saint Gobain tells about this type of crystal scintillator material csi-pure-material-data-sheet_69770 :

“Cesium Iodide is a material with high γ-ray stopping power due to its relative high density and atomic number. Undoped CsI, being an intrinsic scintillator, has very different scintillation proper-ties from the more widely used CsI(Tl) or CsI(Na) activated by Tl or Na respectively.Undoped CsI is mainly used in physics experiments because of its combination of fast timing and relatively high density. Its scintillation is heavily quenched at room temperature, and cooling improves the light output.CsI is slightly hygroscopic”

Pure CsI crystal

I’ve tested it under UV light to see if it’s fluorescent but… no way! It doesn’t lights up under UV.

CsI under UV light