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.

Side-hole type NaI(Tl) crystals has a side-hole passing vertically through the axis of the cylinder of NaI(Tl) crystals, then it is encapsulated in an aluminum housing. The measured specimen could be put inside the hole,  and emitted light from scintilating NaI(Tl) crystals could be obtained from an optical window mounted on top surfaces. Shanghai North Optics offers he customerized side-hole type NaI(Tl) scintillators upon customer's request, the Photomultiplier Tube (PMT) and electronic modules could be integrated with side-hole type NaI(Tl) crystals if it is required.