Europium-doped Strontium Iodide Research Articles

Enrichment measurement by passive γ-ray spectrometry of uranium dioxide fuel pellets using a europium-doped, strontium iodide scintillator

The performance of a europium-doped strontium iodide scintillator for uranium enrichment measurement of a variety of sintered uranium dioxide fuel pellets is described and compared to that of caesium iodide and sodium iodide. Enrichment has been determined via passive γ-ray spectrometry of the 186 keV line from uranium-235 using gross count, net count, and peak ratio analyses. The 38 mm Ø x 38 mm strontium iodide crystal demonstrates superior energy resolution (3.43 ± 0.03% at 662 keV) and competitive detection efficiency for its size in the energy range of interest for uranium enrichment analysis (<250 keV). It demonstrates better χv2 and coefficient of determination values than caesium iodide and sodium iodide when measuring uranium enrichment using the gross- and net-count from the 186 keV emission. It is shown to have the least measurement variance of the three scintillators studied in determining the uranium enrichment of pellets in a blind test, with a relative error comparative to sodium iodide and smaller than caesium iodide. This research heralds the potential of strontium iodide in passive γ-ray uranium enrichment applications.

Initial Performance Testing of Sri Gamma Spectroscopy Scintillators and Comparison to Other Improved-Resolution Detectors for Typical Health Physics Applications

Europium-doped Strontium Iodide (SrI) scintillation gamma detectors have only recently become commercially available. SrI has very high light output ranging from 80,000-100,000 ph/MeV and energy resolution as good as 2.9% at 662 keV and 14.8% at 32 keV. The high density of 4.6 g/cc in combination with a high effective Atomic number and the absence of internal activity make SrI a very attractive sensor material for spectroscopic radiation monitoring devices. This new entrant into the field of commercially available gamma spectroscopy detectors offers improved energy resolution over NaI, without the elevated background of LaBr. While CZT and HPGe detectors have better resolution, the small available size of CZT and the cooling requirement of HPGe limit their usefulness in portable applications. Of these scintillators, SrI2 has the lowest detection limits when compared to other equal- size scintillation detectors, especially at low energies where U and Pu are of interest.

Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation

AbstractThe excellent light yield proportionality of europium-doped strontium iodide (SrI2:Eu) has resulted in state-of-the-art γ-ray detectors with remarkably high-energy resolution, far exceeding that of most halide compounds. In this class of materials, the formation of self-trapped hole polarons is very common. However, polaron formation is usually expected to limit carrier mobilities and has been associated with poor scintillator light-yield proportionality and resolution. Here using a recently developed first-principles method, we perform an unprecedented study of polaron transport in SrI2, both for equilibrium polarons, as well as nascent polarons immediately following a self-trapping event. We propose a rationale for the unexpected high-energy resolution of SrI2. We identify nine stable hole polaron configurations, which consist of dimerised iodine pairs with polaron-binding energies of up to 0.5 eV. They are connected by a complex potential energy landscape that comprises 66 unique nearest-neighbour migration paths. Ab initio molecular dynamics simulations reveal that a large fraction of polarons is born into configurations that migrate practically barrier free at room temperature. Consequently, carriers created during γ-irradiation can quickly diffuse away reducing the chance for non-linear recombination, the primary culprit for non-proportionality and resolution reduction. We conclude that the flat, albeit complex, landscape for polaron migration in SrI2 is a key for understanding its outstanding performance. This insight provides important guidance not only for the future development of high-performance scintillators but also of other materials, for which large polaron mobilities are crucial such as batteries and solid-state ionic conductors.

Fabrication and characterization of rectangular strontium iodide scintillator coupled to TSV-MPPC array

Europium-doped strontium iodide (SrI2(Eu)) is a promising material for the scintillation crystals in a Compton imaging system, which requires an excellent energy resolution, as an alternative to NaI(Tl) crystals. Rectangular SrI2(Eu) crystals with dimensions of 10×10×10mm3 are fabricated, aiming for coupling with semiconductor-based photodetectors, especially silicon photomultipliers (SiPMs) in array detectors. The fabricated crystals are evaluated by coupling with a through silicon via (TSV)-type multipixel photon counter (MPPC) with dimensions of 12.6×12.6mm2. The saturation response of the SiPMs is corrected by using several photopeaks of isotopes with a fitting function. The measured energy resolution is approximately 4.4% at 662keV compared with an energy resolution of 3.4% with a PMT, and the crystals exhibit the best energy resolution with a shaping time of 6μs. All of the five prepared samples exhibit very stable performance and are promising for our future Compton imaging system for environmental radiation monitoring.

Performance evaluation of newly developed SrI2(Eu) scintillator

The development of europium-doped strontium iodide (SrI2(Eu)) has attracted considerable attention, because of its excellent material properties as regards gamma-ray scintillator applications. These include its excellent energy resolution, high light output (>80,000ph/MeV), and high effective atomic number (Z=49). Here we report on the performance of ϕ 1in×1in SrI2(Eu) cylindrical crystals newly fabricated by Union Materials Inc. In this study, we measured the energy resolution and light output at 10 °C temperature intervals between −40 and 40°C, using an optically coupled 2-in photomultiplier tube (PMT) (Super Bialkali, Hamamatsu). The SrI2(Eu) light output increased by 0.12%/°C as the temperature decreased. At −40°C, we obtained the optimal energy resolution recording 2.91±0.02% full width at half maximum (FWHM) for 662keV gamma rays measured with 137Cs. For comparison, we also measured the same crystal using both a large-area (19×19mm2) avalanche photodiode detector (APD) and 8×8 multi-pixel photon counter (MPPC) arrays of 3×3mm2 pixels. The energy resolutions of 2.94±0.02%, 3.14±0.06% and 3.99±0.01% were obtained using PMT, APD, and MPPC, respectively, as measured at −20°C. We also measured the inherent background of SrI2(Eu) in a cave composed of Cu–Pb blocks with their thickness of 5–10cm confirming that SrI2(Eu) has an extremely low inherent background radiation. In this study, we have shown that SrI2(Eu) is a promising scintillator that can be utilized for radiation measurements incorporating low-energy X-rays to high-energy gamma rays, and can thus be applied in various medical, industrial, and environmental treatment fields in the near future.

Characterization of strontium iodide scintillators with silicon photomultipliers

This work characterizes a commercially available europium-doped strontium iodide detector recently developed by Radiation Monitoring Devices (RMD). The detector has been chosen for a space-based mission scheduled to launch in early 2017. The primary goal of this work was to characterize the detector׳s response over the expected operational range of −10°C to 30°C as well as the expected operational voltage range of +26.5–+28.5V and identify background interferences that may develop due to neutron activation produced by cosmic-ray interactions. The 8mm×8mm×20mm detectors use KETEK silicon photomultipliers (SiPM), with an active area of 6mmx6mm (KETEK PM6660). Our results show substantial integral nonlinearity due to the SiPM ranging from 0% to 25% at room temperature over the energy range of 80–2614keV. The nonlinearity, a function of temperature and overvoltage, leads to an underestimate of the full width at half max (FWHM), which is 2.6% uncorrected at 662keV and 3.8% corrected at 662keV. The temperature dependence of the detector results in a noise threshold that increases substantially above 30°C due to the SiPM dark rate. In an effort to simulate the harsh environment of space, neutron activation of the detector was also explored. Gamma-ray lines at 127keV and 164keV were observed in the detector along with Kα x-rays associated with europium. Beta decay from europium- and iodine-activation products were also observed within the detector.

Instrument Development and Gamma Spectroscopy With Strontium Iodide

Development of the Europium-doped Strontium Iodide scintillator, SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Eu), involves advances in crystal growth, optics and readout methodology for prototype detectors. We have demonstrated energy resolution of 3% at 662 keV for a 26 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Eu) crystal, which is equivalent to the performance obtained with Cerium-doped Lanthanum Bromide of equivalent size. Compared to standard analog readout, use of a digital readout method allows improved energy resolution to be obtained with large volume SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Eu) crystals. Comparative gamma spectra acquired with LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) and NaI(Tl) quantitatively depict the value of the high resolution of SrI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Eu) in discriminating closely spaced gamma lines for radioisotope identification applications.

Bridgman growth of large SrI2:Eu2+ single crystals: A high-performance scintillator for radiation detection applications

Single-crystal strontium iodide (SrI2) doped with relatively high levels (e.g., 3–6%) of Eu2+ exhibits characteristics that make this material superior, in a number of respects, to other scintillators that are currently used for radiation detection. Specifically, SrI2:Eu2+ has a light yield that is significantly higher than LaBr3:Ce3+—a currently employed commercial high-performance scintillator. Additionally, SrI2:Eu2+ is characterized by an energy resolution as high as 2.6% at the 137Cs gamma-ray energy of 662keV, and there is no radioactive component in SrI2:Eu2+—unlike LaBr3:Ce3+ that contains 138La. The Ce3+-doped LaBr3 decay time is, however, faster (30ns) than the 1.2μs decay time of SrI2:Eu2+. Due to the relatively low melting point of strontium iodide (∼515°C), crystal growth can be carried out in quartz crucibles by the vertical Bridgman technique. Materials-processing and crystal-growth techniques that are specific to the Bridgman growth of europium-doped strontium iodide scintillators are described here. These techniques include the use of a porous quartz frit to physically filter the molten salt from a quartz antechamber into the Bridgman growth crucible and the use of a “bent” or “bulb” grain selector design to suppress multiple grain growth. Single crystals of SrI2:Eu2+ scintillators with good optical quality and scintillation characteristics have been grown in sizes up to 5.0cm in diameter by applying these techniques. Other aspects of the SrI2:Eu2+ crystal-growth methods and of the still unresolved crystal-growth issues are described here.

Modeling scintillation light absorption and re-emission in SrI2(Eu) scintillators

Abstract Europium-doped strontium iodide has recently attracted interest as a scintillator for gamma-ray spectroscopy. Excellent energy resolution (2.6% FWHM at 662 keV) with SrI2(Eu) has been reported for small (

Prospects for High Energy Resolution Gamma Ray Spectroscopy with Europium-Doped Strontium Iodide

AbstractEuropium-doped strontium iodide scintillators offer a light yield exceeding 100,000 photons/MeV and excellent light yield proportionality, while at the same time, SrI2 is readily grown in single crystal form. Thus far, our collaboration has demonstrated an energy resolution with strontium iodide of 2.6% at 662 keV and 7.6% at 60 keV, and we have grown single crystals surpassing 30 cm3 in size (with lower resolution). Our analysis indicates that SrI2(Eu) has the potential to offer 2% energy resolution at 662 keV with optimized material, optics, and read-out. In particular, improvements in feedstock purity may result in crystal structural and chemical homogeneity, leading to improved light yield uniformity throughout the crystal volume, and consequently, better energy resolution. Uniform, efficient light collection and detection, is also required to achieve the best energy resolution with a SrI2(Eu) scintillator device.