Inorganic Scintillator Crystals
Inorganic crystalline scintillators are single crystals that emit optical radiation upon exposure to X-ray, gamma-ray or neutron radiation. Scintillators composed of alkali, alkaline earth and rare earth halide crystals generally have an activator dopant uniformly dispersed throughout the crystal lattice. The most common scintillator crystal in use today is thallium-doped sodium iodide, NaI:Tl.
Dark matter studies require the development and use of special experimental techniques to detect the signal that dark matter particles emit when they interact with ordinary matter. Because of the extremely low probability of an interaction, these events are exceptionally rare and can only be observed if the numbers of events resulting from other possible origins are minimized. For this reason, dark matter studies are carried out deep in underground laboratories, such as the Gran Sasso in Italy, where the shielding effect of the mountain overlooking the laboratory (1,500 meters of rock) absorbs the majority of the cosmic rays striking the earth’s surface.
The instruments used in this research require detectors fabricated of high sensitivity, ultra-low radioactivity materials to record these rare events and to minimize the possibility of false counts. To construct these specialized detectors, RMD has developed and perfected the manufacturing process to produce extremely pure, high quality scintillator crystals, and to package them with an appropriate photomultiplier tube (PMT).
RMD’s high purity NaI scintillators are grown using the Bridgeman-Stockbarger method and can be produced in the required size and configuration for these dark matter and other high energy physics studies.
Inorganic Scintillator Crystals Manufactured by RMD
- Thallium-doped Caesium Iodide – CsI:Tl
- Sodium-doped Caesium Iodide – CsI:Na
- Europium-doped Lithium Iodide – LiI:Eu
- Europium-doped Calcium Fluoride – CaF2:Eu
- Cadmium Tungstate – CdWO4
Alkaline Earths and Rare Earth Halide Scintillators
In the search for brighter and more responsive scintillators, a major effort has been made to develop improved scintillators from the alkaline earth and the rare earth halide families. These have higher light output, better energy resolution and improved decay times compared to scintillators such as NaI:Tl. Scintillator crystals are coupled to either a photomultiplier tube (PMT) or a Silicon photomultiplier (SiPM) to measure emitted light.
CLYC (Cs2LiYCl6:Ce) is the first practical gamma-neutron scintillation detector for use as a replacement for both medium resolution gamma-ray detectors and Helium-3 proportional counter tubes for neutron detection. The ease of using Pulse Shape Discrimination (PSD) for neutron detection, combined with better gamma-ray resolution than NaI or CsI, make CLYC an ideal solution for several classes of handheld instruments, including personal radiation detectors (PRDs), spectroscopic personal radiation detectors (SPRDs), and radioisotope identification devices (RIIDs). Other applications requiring gamma-neutron detection can also benefit from using CLYC. CLYC is grown using the Bridgeman technique.
CLLBC (Cs2LiLa(Br,Cl)6:Ce) is a gamma-neutron detector for use as a replacement for both high energy resolution gamma-ray detectors and high pressure helium-3 tubes used for neutron detection. The ease of using pulse height as well as pulse shape discrimination for neutron detection, combined with gamma-ray energy resolution better than NaI:Tl or CsI:Tl and in the working range of LaBr3:Ce, makes CLLBC an ideal solution for several classes of handheld instruments, including spectroscopic personal radiation detectors (SPRDs) and radionuclide identification devices (RIIDs). Other applications requiring gamma-neutron detection will also benefit from using CLLBC.
Instrument manufacturers will find the simplicity and compactness of implementing a dual-mode detector to be advantageous. The neutron cross-section of 95% 6Li-enriched CLLBC is 2.5 times that of Helium-3 (10 atmospheres), compared on a volume basis. Due to its highly proportional response, energy resolution for 662 keV gamma rays is typically better than 3.5% using CLLBC (a factor of two improvement over NaI:Tl, depending on the configuration of the detector and photosensor. CLLBC can be packaged with a temperature sensor and a SiPM array.
The resulting CLLBC-SiPM sensor offers a compact package, low voltage requirements, and a reliable signal for neutron detection and gamma-ray spectroscopy.
Strontium Iodide (SrI2:Eu) scintillators are used in instruments that require high resolution gamma-ray spectroscopy due to the high light output and exceptional linearity of the material. SrI2:Eu performs well at both high and low energies and the lack of intrinsic radioactivity reduces background counts and false alarms.
SrI2:Eu scintillators can be employed in a range of hand-held radiation detection instruments, as well as medical, industrial, and environmental applications. Packaged SrI2:Eu scintillators can easily be incorporated into hand-held radiation detectors to significantly enhance their performance as compared to a NaI:Tl scintillator. The energy resolution for 662 keV 137Cs gamma rays using a 1 inch cylinder of SrI2:Eu is better than 4%. SrI2:Eu is available in diameters of up to 1.5-inches as well as custom configuration.
Thallium (Tl) based elpasolites combine the best features of NaI:Tl, LaBr3:Ce and He-3 into one scintillation detector. Tl-based elpasolites provide simultaneous gamma-neutron detection, while enabling pulse shape discrimination between gamma-rays and thermal neutrons. They are expected to satisfy all the key requirements for gamma-ray detectors; high energy resolution, high detection efficiency and low cost. Furthermore, they will provide excellent thermal neutron detection capabilities and good pulse shape discrimination of gamma and neutron events.
Our detectors will provide instrument manufacturers with new alternatives to build high performance, low cost radiation detection instruments. These instruments will be used in nuclear non-proliferation, nuclear treaty verification, environmental monitoring, nuclear waste cleanup, and border security. Oil well logging, medical imaging, nuclear and particle physics experiments, space physics and non-destructive testing are additional applications for Tl-based elpasolites. Tl-based elpasolites are grown using the Bridgeman technique.