Materials Used in Scintillators and Their Assemblies

Saint Gobain Crystals offers technology and product solutions to a wide base of customers. Originally, scintillators were used in nuclear research. From 1944, a phosphor linked to a photomultiplier tube has been used by researchers to successfully detect ionizing radiation. A number of practical commercial applications have since been developed in security and safeguards, health physics, oil exploration, nuclear medicine, and industry.

The philosophy of Saint Gobain Crystals has been the development of basic design and assembly concepts which can be integrated into a nearly limitless range of geometries and sizes, depending upon the radiation required and the application’s constraints and conditions. The final performance and end-use specifications determine the choice of light-sensing device, optical window material, housing material, crystal, etc.

Medical Applications include Planer and SPECT Imaging PET Scanners (Positron Emission Tomography), Surgical Probes BLD (Bone Mass Densitometry), CT Scanners (Computed Tomography), Whole Body Counting, and RIA (Radioimmunoassay).

Geophysical Applications include Multiphase Flow Analysis Aerial (large area) Survey and Wireline Logging MWD (Measurement While Drilling).

Security Applications include Portal Monitoring, Luggage Scanners, Cargo Scanner, and Nuclide Identification.

Industrial Applications include Non-destructive Evaluation, Contamination Monitoring, Nuclear Gauging, and Thermal Neutron Activation Analysis.

Saint-Gobain Crystals' Radiation Sensors Applications Matrix

Sensor <20 keV X-ray 20 to 100 keV X-ray 100 keV to 5 MeV γ-ray > 5 MeV γ-ray Thermal neutron Fast neutron Alpha Beta Charged particles Fast timing, high rate
NaI(Tl)
LaBr3
LYSO
CsI(TI)
CsI(Na)
CsI(Pure)
CaF2(Eu)
BaF2
BGO
CdWO4
Organic Solids
Organic Liquids
Lithium Glasses
G-M Tubes

Material and Geometry Capabilities

An industry leading range of detectors and scintillators are offered by Saint-Gobain. They also continue to develop new scintillators, both with outside partners and internally, in order to meet the needs of both present and future markets.

Internal growth processes and raw material chemistry abilities have been developed by Saint-Gobain for the majority of these materials. They can control performance as they process their raw materials in-house. This gives them particular control over quality consistency and light output.

Additionally, unique packing, cutting, and shaping facilities and equipment have been developed by Saint-Gobain. This enables them to form scintillators into nearly every shape which may be requested.

In order to prevent any degradation during the assembly process, once shaping has occurred, Saint-Gobain's manufacturing facilities are fitted with the climate and environmental conditions which accord with the characteristics of the material. Their extensive experience of packaging hygroscopic materials ensures that detectors will carry on performing in the field for a number of years.

In order to speed up the introduction to the market, Saint-Gobain can provide higher level mechanical and electronic assemblies. This also guarantees proper system performance, particularly when the higher-level assemblies are tested.

Once production levels have increased to high volume production from low volume prototyping, Saint-Gobain boasts an industry-leading capacity in primary scintillators such as sodium iodide. This makes sure that any partnership with Saint-Gobain will enable smooth ramp up with successful introductions to the market.

Standard Assemblies

Four basic designs are provided by Saint-Gobain Crystals: a scintillator integrally mounted to a light-sensing device (for instance, a photomultiplier tube [PMT]), a packaged scintillator, a scintillator array, and a scintillator with a demountable PMT. One or more of the numerous options listed can be incorporated into each of these basic detector configurations.

Basic Packaged Scintillator – This scintillator is a scintillation crystal mounted in a metal container with a low-mass (generally aluminum). The package is hermetically sealed for hygroscopic crystals such as Nal(Tl). Reflector material is put in between the container walls and the scintillator and an optical window is incorporated into one end.

A broad range of shapes and sizes (including rectangular and cylindrical) can be produced. A user-supplied, externally-coupled light-sensing device is necessary for this kind of detector. For particular manufacturing or experimental circumstances in which different scintillator-PMT combinations may be regularly necessary, packaged scintillators are required.

Illustration of Basic Packaged Scintillator

Illustration of Basic Packaged Scintillator

Integrally Mounted Scintillator/Light-sensing Device Assembly – The light-sensing device (generally a PMT) is optically coupled directly to the scintillator in this integral design. A container (normally aluminum) is used to mount the scintillator and a mu-metal shield is placed over the PMT. A hygroscopic scintillator such as Nal (Tl) is used to seal the detector package hermetically.

In order to form a light-tight and low-mass housing for the detector, the mu-metal shield and the scintillator container are sealed together. More consistent and improved energy resolution is normally yielded by this design. Consequently, these detectors are often chosen for radio-isotype or spectroscopy assays.

Illustration of Integrally Mounted Scintillator/PMT Assembly

Illustration of Integrally Mounted Scintillator/PMT Assembly

Demountable Scintillator/PMT Assembly – Enabling the removal of the PMT(s) without disturbing the scintillator package, the demountable designs are scintillator-photomultiplier combinations. Appropriate reflector material is used to mount the scintillator in a low-mass metal container which has an optical window for each PMT.

Each PMT’s magnetic light shield is fastened to the flange mechanically (or any other mounting hardware on the scintillator container). This configuration is ideally suited for applications which require the use of crystals which exceed 5” in diameter or for imaging applications.

Illustration of NaI(Tl) Detector Assembly with Demountable Photomultiplier Tubes

Illustration of NaI(Tl) Detector Assembly with Demountable Photomultiplier Tubes

Crystal Arrays – A number of their scintillation materials are suitable for use with small-pixel arrays. The development of arrays has been pushed by the continued demand for improved resolution, as well as for the availability of better, position-sensitive light sensors. These are now used extensively in industrial imaging, medical, and security industries.

Specialized Assemblies

Specific designs are required for certain applications. These include the phoswich detector for low-energy gamma counting in a background of high energy, or a design which is ruggedized for operating in inhospitable environments. Some of these specialized assemblies are shown below.

Well Designs  – When applications require high detection efficiency, such as for counting applications like RIA (Radioimmunoassay) and Compton suppression, through-side wells and end wells are used. Performance criteria and energies of interest determine the design.

Ruggedized Designs  – Developed for the oil well service industry, ruggedized units are designed in order to cope with high temperatures and/or vibration and shock. In this detector type, epoxy seals are not used. This design can incorporate proprietary interface loading, titanium alloy or stainless-steel housing, and an all-welded assembly. These ruggedized detectors are designed in order to cope with temperatures from -55 degrees centigrade to +205 degrees centigrade, as well as extreme vibration and shock environments.

Harsh Environment Designs – It is possible to custom-design or modify detectors so that they can operate outside of a laboratory environment. Specific requirements may include any of the following environments: severe mechanical shock and vibration, underwater use, elevated temperatures, extreme cold, or use in a vacuum.

Pulser or LED Designs – A common way of stabilizing gain is to build a reference light source into a detector assembly. The source of light produces a spectrum peak outside the region of interest. In order to maintain this peak’s position in the measured spectrum, the system adjusts the gain.

Depending on what the user’s requirements are, detectors with any of the following as the reference light source can be supplied:

  • A 241 Am light pulser
  • An LED imbedded in the optical window
  • A fiber optic cable with an external LED
  • A radioactive source (for instance, 137Cs)

Phoswich Designs – When scintillators which do not have similar pulse shape characteristics are combined with one another, as well as with a common PMT (or PMTs), a phoswich (“phosphor sandwich”) is made. In order to differentiate the signals from the two scintillators, pulse shape analysis is used. This identifies in which of the scintillators the event took place.

Phoswich detectors were designed in order to detect low-energy, low-intensity X-rays and gamma rays, as well as beta and alpha particles, efficiently in a higher-energy ambient background. In order to detect and identify particles, a phoswich detector may also be used in a detector telescope.

Low Background Designs  – It is necessary to reduce the detector background for low level activity measurements. This can be achieved by selecting materials which exhibit the lowest natural radioactivity: (1) low and extremely low background scintillator; (2) instead of a standard glass window, use a quartz window; (3) for the housing, low background aluminum, copper, or stainless steel; (4) specific reflector material as well as other selected components; (5) for low background, PMT is selected.

Thin Entrance Window Designs – Specific crystal thickness, entrance window thickness, and entrance window types are required for low energy X-ray and gamma ray applications. A typical energy range for an assembly with a beryllium entrance window is between 3 and 100 keV. For assemblies with aluminum entrance windows, the typical range is between 10 and 200 keV.

Other Specialized Detector Designs

  • Large spectrometers
  • Annular shields
  • Flat and curved detector plates for nuclear medicine applications
  • Position-measuring detector bars
  • Pair spectrometers
  • Neutron detectors

NaI(Tl) Detector "Crystal Ball" Application: Nuclear Physics

NaI(Tl) Detector "Crystal Ball" Application: Nuclear Physics

BrilLanCe™ 380 Detector Application: Aerospace

LaBr3(Ce) Detector Application: Aerospace

This information has been sourced, reviewed and adapted from materials provided by Saint-Gobain Crystals.

For more information on this source, please visit Saint-Gobain Crystals.

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