Sodium Iodide crystals doped with Thallium (or NaI(Tl) crystals) have a very high scintillation or luminescence efficiency and a good energy resolution, NaI(Tl) scintillators has the largest light-out and an emission range well matched to photomultipliers with bialkali photocathodes at a high efficiency, and combination with its easy availability of variety size and geometries and low cost, NaI(Tl) scintillators has become most widely used scintillators. NaI(Tl) crystals is a kind of highly hygroscopic materials, it must be put in a hermetical sealing housing in using.

The NaI(Tl) crystal is cut into thin disk and polished, then it is encapsulated in an aluminum ring, beryllium or aluminum foil is often used as the entrance window, and thin disk or plate NaI(Tl) crystals are usually used in detection of soft X-rays with low energy levels. Shanghai North Optics supplies the customized thin NaI(Tl) scintillators upon customer's request, the Photomultiplier Tube (PMT) and electronic modules could be integrated with thin disk or plate type NaI(Tl) crystals if it is required.