Thallium doped sodium iodide crystal (NaI:TI) is a high performance scintillation crystal. These crystals are grown from sodium iodide (NaI) as a base material with an appropriate concentration of the activator thallium (TI) and have a maximum luminous wavelength of 415 nm, which is well matched to the photocathode of common photomultiplier tubes.

Nal:TI scintillators are colourless, transparent crystals with no absorption of their own light. Because of its high density and high effective atomic number, it has a strong absorption capacity and high energy resolution for X-rays and “rays, so it occupies an important position in radiation detection, it is an important basic material in the detection instruments of geology, mining, petroleum, coal, medical, security, industrial CT and environmental testing.