Inorganic scintillators are usually crystals grown in high temperature furnaces, for example, alkali metal halides, often with a small amount of activator impurity. The most widely used is NaI(Tl) (thallium-doped sodium iodide); its scintillation light is blue. Other inorganic alkali halide crystals are: CsI(Tl), CsI(Na), CsI(pure), CsF, KI(Tl), LiI(Eu). Some non-alkali crystals include: BaF2, CaF2(Eu), ZnS(Ag), CaWO
4, CdWO4, YAG(Ce) (Y3Al5O12(Ce)), GSO, LSO.
Newly developed products include LaCl3(Ce), lanthanum chloride doped with cerium, as well as a cerium-doped lanthanum bromide, LaBr3(Ce). They are both very hygroscopic (i.e., damaged when exposed to moisture in the air) but offer excellent light output and energy resolution (63 photons/keV γ for LaBr3(Ce) versus 38 photons/keV γ for NaI(Tl)), a fast response (16 ns for LaBr
3(Ce) versus 230 ns for NaI(Tl)), excellent linearity, and a very stable light output over a wide range of temperatures. In addition LaBr3(Ce) offers a higher stopping power for γ rays (density of 5.08 g/cm3 versus 3.67 g/cm3 for NaI(Tl)). LYSO (Lu1.8Y0.2SiO5(Ce)) has an even higher density (7.1 g/cm3, comparable to BGO), is non-hygroscopic, and has a higher light output than BGO (32 photons/keV γ), in addition to being rather fast (41 ns decay time versus 300 ns for BGO).
A disadvantage of some inorganic crystals, e.g., NaI, is their hygroscopicity, a property which requires them to be housed in an airtight container to protect them from moisture. CsI(Tl) and BaF2 are only slightly hygroscopic and do not usually need protection. CsF, NaI(Tl), LaCl3(Ce), LaBr3(Ce) are hygroscopic, while BGO, CaF2(Eu), LYSO, and YAG(Ce) are not.
Inorganic crystals can be cut to small sizes and arranged in an array configuration so as to provide position sensitivity. Such arrays are often used in medical physics or security applications to detect X-rays or γ rays: high-Z, high density materials (e.g. LYSO, BGO) are typically preferred for this type of applications.
Scintillation in inorganic crystals is typically slower than in organic ones, ranging typically from 1.48 ns for ZnO(Ga) to 9000 ns for CaWO4. Exceptions are CsF} (~5 ns), fast BaF2 (0.7 ns; the slow component is at 630 ns), as well as the newer products (LaCl3(Ce), 28 ns; LaBr3(Ce), 16 ns; LYSO, 41 ns).