List of Inorganic Scintillators
The following is a list of commonly used inorganic crystals:
- BaF2 or barium fluoride: BaF2 contains a very fast and a slow component. The fast scintillation light is emitted in the UV band (220 nm) and has a 0.7 ns decay time (smallest decay time for any scintillator), while the slow scintillation light is emitted at longer wavelengths (310 nm) and has a 630 ns decay time. It is used in for fast timing applications, as well as applications for which pulse shape discrimination is needed. The light yield of BaF2 is about 12 photons/keV. BaF2 is not hygroscopic.
- CaF2(Eu) or calcium fluoride doped with europium: The material is not hygroscopic, has a 940 ns decay time, and is relatively low-Z. The latter property makes it ideal for detection of low energy β particles because of low backscattering, but not very suitable for γ detection. Thin layers of CaF2(Eu) have also been used with a thicker slab of NaI(Tl) to make phoswiches capable of discriminating between α, β, and γ particles.
- BGO or bismuth germanate: Bismuth germanate has a higher stopping power, but a lower optical yield than NaI(Tl). It is often used in coincidence detectors for detecting back-to-back gamma rays emitted upon positron annihilation in positron emission tomography machines.
- CdWO4 or cadmium tungstate: a high density, high atomic number scintillator with a very long decay time (14 μs), and relatively high light output (about 1/3 of that of NaI(Tl)). CdWO4 is routinely used for X-ray detection (CT scanners). Having very little 228Th and 226Ra contamination, it is also suitable for low activity counting applications.
- CaWO4 or calcium tungstate
- CsI(Tl) or cesium iodide doped with thallium: these crystals are one of the brightest scintillators. The maximum wavelength of light emission is rather high (550 nm), however, making CsI(Tl) best coupled to red-enhanced PMTs or to photo-diodes. CsI(Tl) is only slightly hygroscopic and does not usually require an air-tight enclosure.
- CsI(Na) or cesium iodide doped with sodium: the crystal is less bright than CsI(Tl), but comparable in light output to NaI(Tl). The wavelength of maximum emission is at 420 nm, well matched to the photocathode sensitivity of bialkali PMTs. It has a slightly shorter decay time than CsI(Tl) (630 ns versus 1000 ns for CsI(Tl)). CsI(Na) is hygroscopic and needs an air-tight enclosure for protection against moisture.
- CsI: undoped cesium iodide emits predominantly at 315 nm, is only slightly hygroscopic, and has a very short decay time (16 ns), making it suitable for fast timing applications. The light output is quite low, however, and very sensitive to variations in temperature.
- Gd2O2S or Gadolinium oxysulfide has a high stopping power due to its relatively high density (7.32 g/cm3) and the high atomic number of gadolinium. The light output is also good, making it useful as a scintillator for x-ray imaging applications.
- LaBr3(Ce) (or lanthanum bromide doped with cerium): a better (novel) alternative to NaI(Tl); denser, more efficient, much faster(having a decay time about ~20ns), offers superior energy resolution due to its very high light output. Moreover, the light output is very stable and quite high over a very wide range of temperatures, making it particularly attractive for high temperature applications. LaBr3(Ce) is very hygroscopic.
- LaCl3(Ce) (or lanthanum chloride doped with cerium): very fast, high light output. LaCl3(Ce) is a cheaper alternative to LaBr3(Ce). It is also quite hygroscopic.
- PbWO4 or Lead tungstate: due to its high-Z, PbWO4 is suitable for applications where a high stopping power is required (e.g. γ ray detection).
- LuI3 or lutetium iodide
- LSO or lutetium oxyorthosilicate (Lu2SiO5): used in positron emission tomography because it exhibits properties similar to bismuth germanate (BGO), but with a higher light yield. Its only disadvantage is the intrinsic background from the beta decay of natural 176Lu.
- LYSO (Lu1.8Y0.2SiO5(Ce)): comparable in density to BGO, but much faster and with much higher light output; excellent for medical imaging applications. LYSO is non-hygroscopic.
- NaI(Tl) or sodium iodide doped with thallium: NaI(Tl) is by far the most widely used scintillator material. It is available in single crystal form or the more rugged polycrystalline form (used in high vibration environments, e.g. wireline logging in the oil industry). Other applications include nuclear medicine, basic research, environmental monitoring, and aerial surveys. NaI(Tl) is very hygroscopic and needs to be housed in an air-tight enclosure.
- YAG(Ce) or yttrium aluminum garnet: YAG(Ce) is non-hygroscopic. The wavelength of maximum emission is at 550 nm, well-matched to red-resistive PMTs or photo-diodes. It is relatively fast (70 ns decay time). Its light output is about 1/3 of that of NaI(Tl). The material exhibits some properties that make it particularly attractive for electron microscopy applications (e.g. high electron conversion efficiency, good resolution, mechanical ruggedness and long lifetime).
- ZnS(Ag) or zinc sulfide: ZnS(Ag) is one of the older inorganic scintillators (the first experiment making use of a scintillator by Sir William Crookes (1903) involved a ZnS screen). It is only available as a polycrystalline powder, however. Its use is therefore limited to thin screens used primarily for α particle detection.
- ZnWO4 or zinc tungstate
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