Single crystal sodium iodide doped with thallium ions is a classic scintillator for detecting gamma-radiation of intermediate and low energies. High luminescence efficiency, wide variety of sizes and geometries and relatively low-cost make NaI(Tl) the most widely used scintillator.
NaI(Tl) scintillators have the greatest light output among all the scintillators and a convenient emission range coinciding with a maximum efficiency of photomultipliers with bialkali photocathodes.
NaI(Tl) crystals have radiation hardness that is quite satisfactory for many applications. They can be used under γ-radiation with flux density of up to 105 photons/(s*cm2) without any noticeable variation of their characteristics.
Wide application of NaI(Tl) crystals is mainly due to relative simplicity of using and low cost of crystals. Because of favorable combination of physical properties, NaI(Tl) scintillators are widely used in different detecting systems in radiation medicine, in apparatus for monitoring of radionuclides, in nuclear physics, high energy physics, etc.
NaI(Tl) Polycrystalline Scintillators
Alongside NaI(Tl) single crystals, Amcrys produces pressed polycrystalline scintillators which have higher temperature and mechanical stability at the same light yield. NaI(Tl) polycrystals are used in outer space studies, for gamma-ray logging in gas and oil industry, in radiation environmental monitoring, etc. Polycrystals can be easily shaped into any desired form and any size. A long NaI(Tl) polycrystals can be used as a position-sensitive detectors with good spectrometric characteristics.
NaI(Tl) polycrystal plates are used for production of imaging detectors for tomographic medical imaging systems.
Thallium doped Cesium Iodide CsI(Tl)
Thallium doped cesium iodide is one of the brightest scintillators with the fluorescence spectrum with maximum at 550 nm, which allows using photodiodes for detection of the emission. Because a scintillator-photodiode pair can be used, it is possible to reduce significantly the size of the detection system, to do without a high-voltage power supply, and to use the detection system in magnetic fields. CsI(Tl) has a high effective atomic number and consequently larger cross-section of the gamma-radiation photoabsorption.
For practical application, it is very important that CsI(Tl) is not hygroscopic. With relatively good radiation hardness (103 rad) it is applied in high-energy physics. Depending on growth conditions CsI(Tl) crystals can be obtained with low afterglow for application in tomographic systems.
Sodium doped Cesium Iodide CsI(Na)
Sodium doped cesium iodide is a good alternative for NaI(Tl) in many standard applications because it has a high light output (85% with respect to NaI(Tl)), the emission in a blue spectral region coinciding with the maximum sensitivity of the most popular PMT with bialkali photocathodes, and hygroscopicity substantially lower than that of NaI(Tl). CsI(Na) crystals, due to their high mechanical strength and thermal stability, are used in the geophysical and cosmic space equipment.
CsI(Na) crystals are used in the experimental high-energy physics as scintillation elements of electromagnetic calorimeters.
Undoped Cesium Iodide CsI(Pure)
Undoped cesium iodide or CsI(pure) has high density, sufficiently small radiation length (1,86 sm) and much lower hygroscopicity than CsI(Tl). CsI(pure) has fluorescence spectrum with maximum at 315 nm with the short decay time (about 16 ns) and long-wave component which allows effectively using this scintillation material for medium- and high-energy physics experiments. Therefore, CsI(pure) can be used when high counting rate is required. CsI(pure) differs from CsI(Tl) and CsI(Na) scintillators by a much faster response and lower light yield.
Undoped CsI has higher radiation stability than when doped with thallium or sodium, and its properties can be largely restored after а certain time. No substantial radiation damage was observed in CsI up to doses of 105 rad.
This material finds its applications in high-energy photon spectroscopy. Undoped CsI can be used in combination with standard glass PMT, though better results are obtained with quartz windows.
Bismuth Germanate BGO
Bismuth germanate Bi4Ge3O12 (BGO) is one of the most widely used heavy oxide scintillation materials. BGO has a high atomic number (83) of the heavy component Bi and a high density of the material (7,13 g/cm3). The luminescence spectrum of BGO scintillators has a maximum in the visible spectral range at 480 nm. Among advantages of BGO crystals, one should note their non-hygroscopicity, mechanical and radiation stability. BGO crystals are stable under radiation doses of up to 103 rad.
Another important advantage of BGO crystals is a nearly complete absence of afterglow. The decay time of the main scintillation component of BGO at room temperature is 300 ns.
All these advantages of BGO crystal are successfully used in experiments of high-energy physics, for creation of small-sized tomography devices and an active protection from background activity.
Polystyrene-based Scintillators
Plastic scintillators are a solid solution of luminophors (luminescent additives), in a transparent polymer (polystyrene (PST). Many characteristics of plastic scintillation materials (light output, transparency to own emission, decay time, radiation resistance) can be varied by changing their composition.
Scintillators with a polystyrene matrix are used to detect alfa-, beta-, gamma- radiation, x-rays and fast neutrons. Plastic scintillators are manufactured by bulk polymerization in aluminium (size up to 7 m) or glass mode casting as well as injection molding process.
By varying the composition, we can produce:
• fast plastic scintillation material: decay time from 0.9 to 0.5 ns, light output 55-50% of anthracene
• plastic scintillation material having the slow decay component: decay time from 300 to 400 ns, light output 45-40% of anthracene
• radiation hard plastics
• plastic scintillation material of elevated radiation resistance
• scintillation polystyrene with the light scattering additive
• scintillation material for dosimetry
• scintillation polystyrene containing soluted organic compounds of heavy elements (Pb – 12%, Sn – 10%)
Plastic detectors are the main component in design of high spatial resolution position sensitive detection system.
Each strip is polystyrene based extruded plastic scintillator with diffused white reflector and optical fiber light readout channel. Existing standard geometry of the strips includes rectangular or triangular shapes with following dimensions: cross sections 10×40 mm, 10×26 mm, 10×10 mm and up to 7000 mm long.
We also offer designing and manufacturing of complete systems (detector/light collection/signal processing and etc.) according to the customer’s specifications.
Plastic Scintillators for n/γ discrimination
Plastic scintillator for n/γ discrimination is a solid solution of different luminescent additives in transparent polystyrene.
Each material has different luminescent addiction which determines its scintillation and mechanical properties. The unique capability of n/γ discrimination arises from strong dependence of scintillation pulse shape produced in gamma and neutron interactions.
Zinc Selenide doped with Tellurium ZnSe(Te)
Zinc Selenide activated with tellurium (ZnSe(Te)) is a scintillator with emission peak at 640 nm, suitable for matching with photodiodes. It is used in x-ray and gamma ray detectors. ZnSe(Te) scintillators are significantly different from the ZnS ones. ZnSe(Te) scintillators have an advantage over other materials during the registration of low-energy X-rays and gamma rays. Developed two versions scintillator ZnSe(Te), having significant differences in the kinetics of luminescence, temperature stability and maximum luminescence bands. This allows to choose the most suitable material for the particular application in the multi-energy X-ray scanners and imagers. The most perspective practical application in the multi-energy X-ray scanners have a composite scintillators based on ZnSe (Te).
They have a high uniformity of scintillation signal by the area, they do not require of the channels separation each other and they have lower price in comparison with traditional pixelated scintillators.
Composite scintillator ZnSe(Te)
Flexible composite scintillators based on zinc selenide doped with tellurium are the development of the Institute for Scintillation Materials. These scintillators are superior to the similar products in the parameters of the light output dispersion, the afterglow level and the sensitivity to X-ray quanta in the energy range of 20-70 keV. The silicone basis of the scintillator and the scintillation zinc selenide powder have a high radiation resistance, resistance to weathering, vibration and mechanical stress. Flexible composite scintillators based on zinc selenide are used in two-energy X-ray scanners, computer tomography, detectors of soft gamma, alpha and beta radiations.
Composite scintillators
Composite scintillator consists of optical transparent media with dispersed granules of scintillator. Composite scintillators possess kinetic and luminescent properties of single crystals. The scintillators effectively detect gamma, beta and X-ray radiation, neutron. Composite scintillators allow manufacturing of large area detectors. This scintillator has high positional sensitivity. Composite scintillators can be used for neutron detection, in the X-ray imaging and high energy physics.
All materials are commercially available (halide crystals, oxide crystals, AIIBVI):
• scintillation crystal granules
• scintillation ceramic (raw materials obtained by chemical synthesis, without crystal growth stage)
Europium doped Lithium Iodide LiI(Eu)
LiI(Eu) is а scintillator mostly used for thermal neutron detection. Neutrons are detected in 6LiI(Eu) through their interaction with the 6Li atoms of the material through the reaction:
This reaction is particularly suitable since no γ-ray is released. The peak for thermal neutrons appears at equivalent γ-ray energy of about 3 MeV, permitting effective discrimination against all natural y-rays.
LiI(Eu) has а light yield of about 30-35% of NaI(TI). The emission consists of а broad band with а maximum at 470 nm. Due to some self absorption in the crystal, large crystal dimensions will degrade the energy resolution.
The decay time for y-rays was measured to be 1.4 µs at room temperature (300К). For the ratio between the response to γ-rays and α-particles/ tritons (light yield per MeV), values around 0.6 are reported. LiI(Eu) is very hygroscopic and is therefore supplied in hermetically sealed detector assemblies.
Rare-earth Garnets (YAG:Ce, LuAG:Ce, GAGG:Ce)
Yttrium aluminium garnet Y3Al5O12:Ce (YAG:Ce) and Lutetium Aluminum Garnet activated by cerium (Lu3Al5O12:Ce, LuAG:Ce) are fast and bright scintillation materials. The decay time is 70-100 ns. This is of advantage in time dependent and coincidence measurements. The wavelength of scintillation emission is about 530-550 nm, which is ideal for photodiode and avalanche diode readout.
LuAG is a good alternative to dense and fast rare-earth orthosilicate scintillators (LSO:Ce, GSO:Ce, LYSO:Ce). The material is mechanically and chemically stable with no cleavage and hygroscopicity. The material can be machined into a variety of shapes and sizes including prisms, spheres and thin plates. Recently developed Gd3Al5-xGaxO12:Ce (GAGG:Ce) with the light yield up to 50000 phot/MeV are the brightest known oxide scintillators.
These materials can be used for high energy gamma and charged particle detection, positron emission tomography matrices, high spatial resolution imaging screens for x-rays, gamma and beta.
Rare-earth Orthosilicates (LGSO:Ce, YSO:Ce)
Ce-doped rare-earth orthosilicate of lutetium and gadolinium, chemical formula Lu2xGd2-2xSiO5:Ce (LGSO:Ce), is a dense, fast scintillation material. It belongs to the family of rare earth silicates, which are known scintillators used in medical equipment, high energy physics, well-logging, x-ray radiography. The energy resolution (6.7–7%) is by 2-4 % better compared to the LSO:Ce and LYSO:Ce analogs. Afterglow in LGSO:Ce is by 2 orders of magnitude lower in comparison with lutetium orthosilicate (LSO:Ce).
Y2SiO5:Ce (YSO:Ce) is a bright and fast light scintillator with the emission peaked at 420 nm. The main component of scintillation decay is 45 ns, the contribution of slower component (>100 ns) not exceeds 5 %. Mechanical processing of YSO:Ce and LGSO:Ce scintillators is easier compared to other silicates.