CZT the principles of operation

CZT detectors are fabricated with very thin metalized electrode geometries deposited on the detector surfaces. These electrodes are then electrically biased creating a difference in electrical potential within the detector volume. When ionizing radiation interacts with the CZT crystal, a large number of pairs of electrons and holes are created in proportion to the energy of the incoming radiation.

The negatively charged electrons and positively charged holes then migrate to the oppositely charged electrodes where they are collected. The resulting charge pulse is then detected by the preamplifier, which produces a voltage pulse whose height is proportional to the incident energy of the incoming photon. The signal from the preamplifier is then fed into a shaping amplifier that converts the signal into a Gaussian pulse and amplifies it. The signal can then be fed into a standard counting system or Multi-Channel Analyzer (MCA) to generate the characteristic spectrum for the incoming photons. We usually couple the cadmium zinc telluride CZT-based detector to an ASIC (application specific integrated circuit) to reduce the size and cost of the readout electronics.

FROM:Kromek

SAPPHIRE IS HIGHLY ROBUST AT EXTREME TEMPERATURES

  • A supported sapphire lens, prism and other custom shapes can be taken up to 1950C with no change to its shape and minimal reduction to mechanical performance
  • Sapphire optics have the highest temperature rating of all optical materials in both oxidizing and inert atmospheres. Combined with extreme chemical resistance, sapphire ball lenses, prisms and other sapphire optics are the go to material for extreme environments.

Cadmium zinc telluride

Cadmium zinc telluride, (CdZnTe) or CZT, is a compound of cadmium, zinc and tellurium or, more strictly speaking, an alloy of cadmium telluride and zinc telluride. A direct bandgap semiconductor, it is used in a variety of applications, including semiconductor radiation detectors, photorefractive gratings, electro-optic modulators, solar cells, and terahertz generation and detection. The band gap varies from approximately 1.4 to 2.2 eV, depending on composition.

Radiation detectors using CZT can operate in direct-conversion (or photoconductive) mode at room temperature, unlike some other materials (particularly germanium) which require liquid nitrogen cooling. Their relative advantages include high sensitivity for x-rays and gamma-rays, due to the high atomic numbers of Cd and Te, and better energy resolution than scintillator detectors. CZT can be formed into different shapes for different radiation-detecting applications, and a variety of electrode geometries, such as coplanar grids and small pixel detectors, have been developed to provide unipolar (electron-only) operation, thereby improving energy resolution.

From Wikipedia, the free encyclopedia

SAPPHIRE OPTICS TRANSMIT LIGHT FROM BELOW 190NM TO OVER 5 MICRONS

A sapphire optical lens is the ideal optical material for many UV and I applications because it can transmit so far into the UV and IR wavelengths. With its thermal and chemical robustness, a sapphire window can be exposed to extreme plasmas and temperatures, far greater than any other material, and continue to transmit high powered UV, visible and IR for years with no degradation. These properties make it an ideal material for UV/VIS/IR sensors, IR surveillance and recon and broad band inspection equipment (especially when abradants are involved).

Sapphire windows are the ideal material for pyrometry. They transmit a wide range of wavelengths hile safely isolating hot zones up to 2000C from external room temperature observation. This makes sapphire windows the ideal sight window material for furnaces and high temperature processing equipment.

Sapphire custom shapes for medical and dental tools that require UV sterilization and curing and IR thermal processing are typical applications where sapphire lenses and transparent tools excel.

FROM:Rayotek Scientific

WHY ARE SAPPHIRE OPTICS & SAPPHIRE MECHANICAL PARTS SUCH HIGH PERFORMERS?

SAPPHIRE LENSES, BALLS & PRISMS ARE INCREDIBLY HARD, STRONG & WEAR RESISTANT:
A sapphire lens can be exposed to extreme abradants such as sand and particulates with minimal effect on the clarity of the optics. This makes sapphire optics the ideal material for a variety of applications such as: aerospace lenses, downhole and drilling vision system optics, inspection windows, watch crystals and gun sights.
Sapphire lenses and sapphire prisms can take pressure like no other clear material, making sapphire optics the go-to transparent material for highpressure vessels, deep sea windows and sight glasses. Combined with the exceptional thermal and chemical performance of sapphire, a sapphire lens is the ideal transparency for pressurized in-process, deep sea and equipment sensors.

Inorganic crystals

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).

Plastic scintillators

The term “plastic scintillator” typically refers to a scintillating material in which the primary fluorescent emitter, called a fluor, is suspended in the base, a solid polymer matrix. While this combination is typically accomplished through the dissolution of the fluor prior to bulk polymerization, the fluor is sometimes associated with the polymer directly, either covalently or through coordination, as is the case with many Li6 plastic scintillators. Polyethylene naphthalate has been found to exhibit scintillation by itself without any additives and is expected to replace existing plastic scintillators due to higher performance and lower price.The advantages of plastic scintillators include fairly high light output and a relatively quick signal, with a decay time of 2–4 nanoseconds, but perhaps the biggest advantage of plastic scintillators is their ability to be shaped, through the use of molds or other means, into almost any desired form with what is often a high degree of durability.Plastic scintillators are known to show light output saturation when the energy density is large (Birks’ Law).

Bases
The most common bases used in plastic scintillators are the aromatic plastics, polymers with aromatic rings as pendant groups along the polymer backbone, amongst which polyvinyltoluene (PVT) and polystyrene (PS) are the most prominent. While the base does fluoresce in the presence of ionizing radiation, its low yield and negligible transparency to its own emission make the use of fluors necessary in the construction of a practical scintillator. Aside from the aromatic plastics, the most common base is polymethylmethacrylate (PMMA), which carries two advantages over many other bases: high ultraviolet and visible light transparency and mechanical properties and higher durability with respect to brittleness. The lack of fluorescence associated with PMMA is often compensated through the addition of an aromatic co-solvent, usually naphthalene. A plastic scintillator based on PMMA in this way boasts transparency to its own radiation, helping to ensure uniform collection of light.

Other common bases include polyvinyl xylene (PVX) polymethyl, 2,4-dimethyl, 2,4,5-trimethyl styrenes, polyvinyl diphenyl, polyvinyl naphthalene, polyvinyl tetrahydronaphthalene, and copolymers of these and other bases.
Fluors
Also known as luminophors, these compounds absorb the scintillation of the base and then emit at larger wavelength, effectively converting the ultraviolet radiation of the base into the more easily transferred visible light. Further increasing the attenuation length can be accomplished through the addition of a second fluor, referred to as a spectrum shifter or converter, often resulting in the emission of blue or green light.

Common fluors include polyphenyl hydrocarbons, oxazole and oxadiazole aryls, especially, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), 1,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD), and 2-(4’-tert-butylphenyl)-5-(4’’-biphenylyl)-1,3,4-oxadiazole (B-PBD).

Properties of scintillators

There are many desired properties of scintillators, such as high density, fast operation speed, low cost, radiation hardness, production capability and durability of operational parameters. High density reduces the material size of showers for high-energy γ-quanta and electrons. The range of Compton scattered photons for lower energy γ-rays is also decreased via high density materials. This results in high segmentation of the detector and leads to better spatial resolution. Usually high density materials have heavy ions in the lattice (e.g., lead, cadmium), significantly increasing the photo-fraction (~Z4).[further explanation needed] The increased photo-fraction is important for some applications such as positron emission tomography. High stopping power for electromagnetic component of the ionizing radiation needs greater photo-fraction; this allows for a compact detector. High operating speed is needed for good resolution of spectra. Precision of time measurement with a scintillation detector is proportional to √τsc. Short decay times are important for the measurement of time intervals and for the operation in fast coincidence circuits. High density and fast response time can allow detection of rare events in particle physics. Particle energy deposited in the material of a scintillator is proportional to the scintillator’s response. Charged particles, γ-quanta and ions have different slopes when their response is measured. Thus, scintillators could be used to identify various types of γ-quanta and particles in fluxes of mixed radiation. Another consideration of scintillators is the cost of producing them. Most crystal scintillators require high-purity chemicals and sometimes rare-earth metals that are fairly expensive. Not only are the materials an expenditure, but many crystals require expensive furnaces and almost six months of growth and analyzing time.

Several other properties are also desirable in a good detector scintillator: a low gamma output (i.e., a high efficiency for converting the energy of incident radiation into scintillation photons), transparency to its own scintillation light (for good light collection), efficient detection of the radiation being studied, a high stopping power, good linearity over a wide range of energy, a short rise time for fast timing applications (e.g., coincidence measurements), a short decay time to reduce detector dead-time and accommodate high event rates, emission in a spectral range matching the spectral sensitivity of existing PMTs (although wavelength shifters can sometimes be used), an index of refraction near that of glass (≈1.5) to allow optimum coupling to the PMT window. Ruggedness and good behavior under high temperature may be desirable where resistance to vibration and high temperature is necessary (e.g., oil exploration). The practical choice of a scintillator material is usually a compromise among those properties to best fit a given application.

Among the properties listed above, the light output is the most important, as it affects both the efficiency and the resolution of the detector (the efficiency is the ratio of detected particles to the total number of particles impinging upon the detector; the energy resolution is the ratio of the full width at half maximum of a given energy peak to the peak position, usually expressed in %). The light output is a strong function of the type of incident particle or photon and of its energy, which therefore strongly influences the type of scintillation material to be used for a particular application. The presence of quenching effects results in reduced light output (i.e., reduced scintillation efficiency). Quenching refers to all radiationless de‑excitation processes in which the excitation is degraded mainly to heat. The overall signal production efficiency of the detector, however, also depends on the quantum efficiency of the PMT (typically ~30% at peak), and on the efficiency of light transmission and collection (which depends on the type of reflector material covering the scintillator and light guides, the length/shape of the light guides, any light absorption, etc.). The light output is often quantified as a number of scintillation photons produced per keV of deposited energy. Typical numbers are (when the incident particle is an electron): ≈40 photons/keV for NaI(Tl), ~10 photons/keV for plastic scintillators, and ~8 photons/keV for bismuth germanate (BGO).

Scintillation detectors are generally assumed to be linear. This assumption is based on two requirements: (1) that the light output of the scintillator is proportional to the energy of the incident radiation; (2) that the electrical pulse produced by the photomultiplier tube is proportional to the emitted scintillation light. The linearity assumption is usually a good rough approximation, although deviations can occur (especially pronounced for particles heavier than the proton at low energies).

Resistance and good behavior under high-temperature, high-vibration environments is especially important for applications such as oil exploration (wireline logging, measurement while drilling). For most scintillators, light output and scintillation decay time depends on the temperature. This dependence can largely be ignored for room-temperature applications since it is usually weak. The dependence on the temperature is also weaker for organic scintillators than it is for inorganic crystals, such as NaI-Tl or BGO. Strong dependence of decay time on the temperature in BGO scintillator is used for remote monitoring of temperature in vacuum environment. The coupled PMTs also exhibit temperature sensitivity, and can be damaged if submitted to mechanical shock. Hence, high temperature rugged PMTs should be used for high-temperature, high-vibration applications.

Applications for scintillators

Scintillators are used by the American government as Homeland Security radiation detectors. Scintillators can also be used in particle detectors, new energy resource exploration, X-ray security, nuclear cameras, computed tomography and gas exploration. Other applications of scintillators include CT scanners and gamma cameras in medical diagnostics, and screens in older style CRT computer monitors and television sets.

The use of a scintillator in conjunction with a photomultiplier tube finds wide use in hand-held survey meters used for detecting and measuring radioactive contamination and monitoring nuclear material. Scintillators generate light in fluorescent tubes, to convert the ultra-violet of the discharge into visible light. Scintillation detectors are also used in the petroleum industry as detectors for Gamma Ray logs.

Lithium Tantalate (LiTaO3) Crystals and Wafers

Hangzhou Shalom EO offers the SAW grade lithium Tantalate (or LiTaO3) crystals s and wafers, advanced facilities are equipped for crystals growing, wafer cutting, wafer lapping, wafer polishing and wafer checking, all finished products are passed at Testing of curie Temp and QC inspections. The SAW grade LiTaO3 crystals boules, blanks, wafer blanks and polished wafers are available upon customer’s request.

Hangzhou Shalom EO supplies the LiTaO3 crystals boules and SAW wafers with diameter 3”, 4” and 6” , some typical SAW wafer modules are listed below, we have stocked wafers for some modules.

And the customized boules or wafers are available upon customer’s request.

Table 1. LiTaO3 crystals boules or blanks

Growth orientation X,Y,Z, Y36, Y42, X-112Y,Y128
Diameter 3”, 4”, 6” or customized
Length <100mm
Polishing Both end surfaces inspection polishing

Note: the customized boules are available upon request.

Table 2. LiTaO3 SAW wafers of 3”, 4” and 6” diameter

Orientation Diameter Thickness Surface finish

(+) plane (-) plane

Surface processing
Y-Cut

36°Y –Cut

42°Y –Cut

48°Y -Cut

128°Y –Cut

X-112°Y -Cut

76.2mm

100.0mm

150.0mm

0.25mm

0.35mm

0.50mm

Mirror polished GC1000# or

GC2000#

White or Pyro-free

Note: The customized wafers are available upon request.