SrI2 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.

Growth difficulties and growth of crack free Eu2+ activated KSr2I5 scintillator single crystal by vertical bridgman-stockbarger technique for radiation detection applications

Europium activated potassium strontium iodide (KSr2I5:0.5Eu2+) compound was synthesized and refined by indigenous zone-refinement experimental set-up. The impurities that are insoluble in the KSr2I5:Eu2+ compound was filtered by using a specifically programmed dual chamber quartz ampoule with frit filter method. Temperature profile of this in-house built vertical transparent Bridgman-Stockbarger technique growth furnace is optimized to grow quality single crystals of KSr2I5:Eu2+. From the photoluminescence emission spectrum a typical 4f6 5d1 – 4f7 transition is observed for a broad emission peak at 432 nm whereas a broad emission peak at 448 nm was obtained from the X-ray excited radioluminescence spectrum. The gamma ray spectrometer was administered to detect the scintillation properties of the grown crystal. The scintillation decay time was calculated for the KSr2I5:Eu2+ crystal wherein the energy resolution under 137Cs sealed gamma source is found to be 3.5 % at 662 KeV.

The impact of strontium composition on thallium-doped cesium iodide scintillators

Investigating new scintillators with more alternative methods has been an attractive topic for a long time. This work aims to study the impact of strontium composition on thallium-doped cesium iodide scintillators. There are three different composition ratios of cesium iodide and strontium iodide precursors of 99:1, 95:5, and 90:10 with the same thallium doping of 0.28 mol%. The EDS measurements analyzed the soluble Sr-compositions in these grown crystals as 0%(undetectable), 0.43%, and 2.31%, respectively. With slightly increased strontium composition, the crystallite size was slightly smaller from 59.17, 45.51, to 33.23 nm, respectively. Moreover, the crystals have a somewhat more compressive strain and a slightly higher single crystallinity when the composition of strontium iodide increases. By analyzing the crystals' optical properties, the luminescent properties were trivially enhanced with a bit higher scintillation light yielding up to 29,859 photon/MeV of the crystal with a Sr-composition of 2.31%. Photoluminescence measurements exhibit the enhanced 520 nm scintillation and the lower 410 nm emission at higher Sr contents. These crystals’ emission decay times were obtained as τ1 = 500 ns (fast component) and τ2 = 700 ns (slow component) and slightly slower times with a higher Sr content. Lastly, radiation detection efficiency has been investigated at various energy levels of gamma rays from Am-241, Co-57, Ba-133, and Cs-137 sources. We found that the crystal with a higher Sr composition of 2.31% has better energy resolutions down to the best one of 7.9% at 662-keV measurement. In summary, higher strontium codoping with thallium in cesium iodide scintillators can enhance the crystal structure and optical properties. This would be one candidate of the promising scintillators for developing alternative high-performance radiation detectors for high-speed imaging applications.

A stilbene–strontium iodide based radioxenon detection system for monitoring nuclear explosions

Atmospheric measurement of noble gases has been extensively used for monitoring nuclear weapon explosions for many years. The ratios of four xenon isotopes of interest (131mXe, 133mXe, 133Xe, and 135Xe) help in discriminating steady state reactor operations from nuclear tests. A new coincidence-based detection system using stilbene and strontium iodide [SrI2(Eu)] for electron and photon detection respectively was developed at Oregon State University to address some of the challenges of the radioxenon systems deployed in the field such as memory effect, and poor energy resolution. Silicon photomultipliers (SiPMs) were used for detecting optical photons from all scintillation media. Real-time coincidence identification was achieved using the eight-channel digital pulse processor. The detection system was evaluated using lab check sources and Oregon State TRIGA reactor irradiated xenon samples. A 48-hour background coincidence spectrum was collected yielding a coincidence count rate and background rejection rate of 0.0174 ± 0.0003 counts per second (cps) and 98.9% respectively. The minimum detectable concentration (MDC) of the system was evaluated to be 0.11, 0.13, 0.20, and 0.73 mBq/m3 for 131mXe, 133mXe, 133Xe, and 135Xe, respectively. The memory effect of the detection system was found to be 0.069 ± 0.015%, which is almost a 70-fold reduction compared to traditional plastic scintillators. The detection elements, custom-designed electronics, and the detector response to radioxenon are detailed in this work.

Stabilization of light emitting Eu2+ centers inside Ca(Sr)I2:Eu particles in glass ceramics. The preliminary concept of synthesis

Glass ceramics in the form of MI2:Eu crystalline particles grown in MO-B2O3 glass (M = Ca, Sr, Ba) through recrystallization from the alloyed melt were fabricated. Eu2+ ions were detected in the CaI2 and SrI2 crystalline particles (not in the BaI2) inside the corresponding glasses. Some amount of Eu2+ centers are expected to originate from the MO-B2O3 glass hosts as well. This was confirmed by correlated electron paramagnetic resonance (EPR), photo- and radioluminescence (PL, RL) measurements. Peculiarities of the Eu2+ distribution and incorporation into the glass ceramics samples as well as charge and energy transfer properties are discussed in detail. Optimal conditions leading to the enhancement of the Eu2+ emission from the CaI2 and SrI2 crystallites inside the glasses were determined.

Fabricating efficient and stable quasi-3D and 3D/2D perovskite solar cells with 2D-sheets connected by inorganic type ionic-bond

In this work, we report a novel two-dimensional (2D) (SrBr)2PbI4 perovskite layered architecture, which were formed by the reaction of strontium bromide (SrBr2), strontium iodide (SrI2) and lead iodide (PbI2). Formation of 2D (SrBr)2PbI4 was verified by small angle XRD peak at 6.4°, which corresponds to the layer distance of 13.78 Å. The best one of solar cells fabricated with Quasi-3D perovskite, (SrBr)2FA59Pb60I181 (n = 60), showed a power conversion efficiency (PCE) of 18.46% and retained 95% of the initial PCE at 1000 h in the dry air. Further, the 2D (SrBr)2PbI4 as the surface passivation layer on the 3D FAPbI3 perovskite greatly reduced the defects at the perovskite/Spiro-OMeTAD interface, and the corresponding solar cells with FAPbI3/(SrBr)2PbI4 3D/2D structure achieved a PCE of 22.14% and over 90% retention of the original PCE at 1000 h. In short, this work provides an example of inorganic complex cations that can form 2D perovskites and achieve perovskite solar cells with high PCE and stabilization at the same time.

Synthesis and Adsorption Properties of Gadolinium-Imprinted Divinylbenzene-Based Copolymers.

Ion-imprinted divinylbenzene and methacrylic acid copolymers for rare-earth element adsorption with crosslink ratios 60 and 40% have been synthesized. Ion imprinting has been carried out via the trapping approach. Alizarin red S has been incorporated in the polymers as a nonvinylated ligand. The obtained materials were characterized via scanning electron microscopy and Fourier transform infrared spectroscopy. Synthesized polymers exist as gel-type nonporous spherical agglomerates from 2 to 6 μm with low surface areas. The sorption properties of the synthesized polymers with respect to lanthanides in static and dynamic modes have been studied. The most efficiently synthesized materials extract rare earth elements from solutions at pH 4–7. The maximum sorption capacity of the obtained polymers with regard to Gd is around 0.5 mmol/g. According to the obtained results, the imprinted polymer with a crosslink ratio 60% is characterized by the highest values of distribution coefficients for lanthanides. The total lanthanide breakthrough capacity for this polymer is 0.861 μmol/g. The adsorption column has been constructed using the imprinted polymer with a crosslink ratio 60%. The column extraction and preconcentration procedure for the trace Eu content determination in the strontium iodide recycled material by inductively coupled plasma–atomic emission spectrometry at a level of 1 × 10–6%(mass) has been proposed.

Radiation damage assessment of SensL SiPMs

Silicon Photomultipliers (SiPMs) are quickly replacing traditional photomultiplier tubes (PMTs) as the readout of choice for gamma-ray scintillation detectors in space. While they offer substantial size, weight and power saving, they have shown to be susceptible to radiation damage. SensL SiPMs with different cell sizes were irradiated with 64 MeV protons and 8 MeV electrons. In general, results show larger cell sizes were more susceptible to radiation damage with the largest 50μm SiPMs showing the greatest increase in current as a function of dose. Current increases were observed for doses as low at ∼2 rad(Si) for protons and ∼20 rad(Si) for electrons. The U.S. Naval Research Laboratory’s (NRL) Strontium Iodide Radiation Instrument (SIRI-1) experienced a 528μA increase in the bias current of the onboard 2x2 SensL J-series 60035 SiPM over its one-year mission in sun-synchronous orbit. The work here focuses on the increase in bulk current observed with increasing radiation damage and was performed to better quantify this effect as a function of dose for future mission. These include the future NRL mission SIRI-2, the follow on to SIRI-1, Glowbug and the GAGG Radiation Instrument (GARI).

A Comparative Study for Application of Pitzer and ePC-SAFT Equations to Predict Volumetric and Saturation Properties in “Formation” Water

Predictions of salt solubility, brine vapor pressure and density are necessary to plan subsurface and surface operations. In this work, a comparative study was conducted to investigate prediction capabilities for salt solubility, equilibrium and volumetric properties of several minerals in “Formation” water by the Pitzer model (a commonly used industrial model) and by the ePC-SAFT equation of state (EOS). To achieve this, several validation and comparison steps were considered for reliable implementation of both models. Firstly, solubility, brine densities and vapor pressures for single-salt solutions were predicted. Afterward, the models’ applications were extended to several mixtures of two salts to predict solubility compared to experimental data from available literature. ePC-SAFT shows promising accuracy. The average relative deviation for prediction of liquid density (which cannot be estimated with the Pitzer model) for single-salt solutions of NaBr, KCl, NaCl and Na2SO4 are 1.13%, 0.70%, 1.02% and 0.36%, respectively. The average relative deviation from experimental data of vapor pressure for mixtures of NaCl and KBr is 0.75% and for mixtures of NaBr and KCl is 0.74% for systems with different concentrations. Moreover, a stochastic regression procedure is presented to evaluate the ePC-SAFT parameters. This technique is used for strontium in different salt solutions. The average relative deviation for mean ionic activity coefficients calculated by ePC-SAFT from experimental data using the ePC-SAFT parameters of strontium from the work of Held et al. [1] for single-salt solutions of strontium chloride, strontium bromide, strontium iodide, strontium nitrate and strontium perchlorate are 19.73%, 19.96%, 15.15%, 14.95% and 25.70%, respectively. These values using the ePC-SAFT parameters of strontium regressed in this work are 6.98%, 10.13%, 8.33%, 9.59% and 10.08%, respectively. Finally, the solubility of different salts was studied for mixing of formation water (FW) and injection water (SW).

Stress‐Driven Phase Transitions of SrI2: A First‐Principles Investigation

The structural and electronic properties of strontium iodide (SrI2) under hydrostatic and nonhydrostatic compressions up to 20 GPa are investigated using first‐principles calculations. Upon hydrostatic compression, SrI2 undergoes a phase transition from the Pbca structure to a quasilayered Pbcm structure around 13.2 GPa, and the bandgap narrows with increasing pressure. Upon uniaxial compression, the system exhibits strong anisotropy. Along [010], a Pbca → Cmcm phase transition is observed at about 16.8 GPa via an intermediate metastable Pbcm structure, whereas along [100] and [001], the Pbca structure remains with cell shape changed. These phase transitions are systematically analyzed with shear moduli, band structures, and densities of states. The suitable bandgaps manifested during its uniaxial compression are exploited for optical and semiconductor 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.

Alkaline Earth Metal Template (Cross-)Coupling Reactions with Hybrid Disila-Crown Ether Analogues.

Alkaline earth metal iodides were used as templates for the synthesis of novel silicon‐based ligands. Siloxane moieties were (cross‐)coupled and ion‐specific, silicon‐rich crown ether analogues were obtained. The reaction of 1,2,7,8‐tetrasila[12]crown‐4 (I) and 1,2‐disila[9]crown‐3 (II) with MgI2 yielded exclusively [Mg(1,2,7,8‐tetrasila[12]crown‐4)I2] (1). The larger Ca2+ ion was then employed for cross‐coupling of I and II and yielded the complex [Ca(1,2,7,8‐tetrasila[15]crown‐5)I2] (2). Cross‐coupling of I and 1,2,4,5‐tetrasila[9]crown‐3 (III) with SrI2 enables the synthesis of the silicon‐dominant 1,2,4,5,10,11‐hexasila[15]crown‐5 ether complex of SrI2 (3). Further, the compounds [Sr(1,2,10,11‐tetrasila[18]crown‐6)I2] (4), [Sr(1,2,13,14‐tetrasila[24]crown‐8)I2] (5), and [Sr(1,2,13,14‐tetrasila‐dibenzo[24]crown‐8)I2] (6) were obtained by coupling I, 1,2‐disila[12]crown‐4 (IV) or 1,2‐disila‐benzo[12]crown‐4 (V), respectively. Using various anions, the (cross‐)coupled ligands were also observed in an X‐ray structure within the mentioned complexes. These template‐assisted (cross‐)couplings of various ligands are the first of their kind and a novel method to obtain macrocycles and/or their metal complexes to be established. Further, the Si−O bond activations presented herein might be of importance for silane or even organic functionalization.

Developing new SrI2 and β-D-fructopyranose-based metal-organic frameworks with nonlinear optical properties.

In the context of personalized medicine, there is a growing interest in materials bearing at the same time diagnostic and therapy functions. This article reports a cheap and easily reproducible procedure to obtain materials with a high potential for these applications. Three new strontium iodide-fructose-based metal-organic frameworks with formulae [Sr(C6H12O6)2]I2, [Sr2(C6H12O6)3(H2O)3]I4·0.5H2O and [Sr(C6H12O6)(H2O)3I]I differing in stoichiometry, symmetry and crystal packing, were obtained and characterized by X-ray diffraction. Bulk quantum simulations show that both the ions and the sugar are crucial in determining the predicted nonlinear response; also, the relative arrangement of various functional groups in the unit cell plays a role in the computed optical properties. Small fragments of the three compounds were selected for in vacuo calculations, proving that the reduced dimensions of the particles have a great influence on the nonlinear optical response. Despite the similar chemical composition of the three compounds, second harmonic generation measurements and in crystal and in vacuo theoretical calculations agree that one of the compounds is a much more efficient second harmonic emitter than the other two, and is thus a suitable candidate for bio-sensor applications.

Determination of the crystallographic orientation of SrI2 crystals

Single crystals of strontium iodide (SrI2), an important material for nuclear detector applications, are grown commercially in cylindrical ampoules using the Bridgman self-seeding method. As a result, the axial orientation of Bridgman boules varies from run to run. Most crystal growth methods benefit from the use of oriented seeds, which can be helpful in maximizing growth rates and crystal quality. However, it is very difficult to orient SrI2 crystals because they are deliquescent and their surfaces damage easily during cutting and polishing. In this study, unpolished facets formed on an edge-defined film-fed growth (EFG) boule were used to generate the first Laue patterns. The principal boule used in this study had a square cross section and was grown using a seed cut from along the growth axis of a Bridgman boule. X-ray analysis showed that the EFG boule grown from this seed grew along the b-axis and the side facets were the (1 0 0) and (0 0 1) faces. This work made possible the fabrication of oriented SrI2 seeds for use in future EFG and Czochralski growth experiments and allowed for the determination of the optic axes using polarized light.

Difficulties and improvement in growth of Europium doped Strontium Iodide (SrI2:Eu2+) scintillator single crystal for radiation detection applications

The molten salt of Strontium Iodide (SrI2) and Europium Iodide (EuI2) was filtered by specially designed dual chamber quartz ampoule using micro frit filter. Eu2+ doped SrI2 single crystal was grown by modified transparent vertical Bridgman technique. Photoluminescence (PL) excitation and emission (PLE) were recorded for the grown crystal. The characteristic emission of Eu2+ was observed at 432 nm. Similar emission was observed at 435 nm, when the sample was excited by X-ray source also. Scintillation properties of the SrI2:Eu2+ crystal were checked by the gamma ray spectrometer using 137Cs, 57Co and 60Co gamma sources. The energy resolutions of the grown crystal were found to be 4.6% at 662 KeV, 7.5% at 122 KeV and 9.8% at 1332 KeV. The Scintillation decay profile was also analyzed. The scintillation decay time of Eu2+ ion was calculated to be 1.26 μs for SrI2:Eu2+ single crystal.

Alkali and Alkaline Earth Metal Derivatives of Disila-Bridged Podands: Coordination Chemistry and Structural Diversity.

Within this study, the synthesis and coordination chemistry of open-chain ligands bearing disila-units is presented. Instead of basic 1:1 complexes, structural diversity was discovered in the variety of ligand and salt. Stable complexes of alkali and alkaline earth metal complexes were obtained by equimolar reactions of different salts with the disila-bridged podands 8,9-disila-EO5 (1) and 11,12-disila-EO7 (2) (EO5 = pentaethylene glycol; EO7 = heptaethylene glycol). The respective alkaline earth metal complexes of the type [Ca(8,9-disila-EO5)(OTf)2] (3), [Sr(8,9-disila-EO5)I2] (5), [Sr(11,12-disila-EO7)I]I (6), and [Ba(11,12-disila-EO7)OTf2] (7) (OTf = CF3SO3-) were characterized via single-crystal X-ray diffraction analyses. Within the reaction of the alkali metal salt NaPF6 with 1, the sodium ion acts as a template during the complexation process. Under elimination of one molecule of diethylene glycol, the dinuclear species [Na2(8,9,17,18-tetrasila-EO8)(PF6)2]·EO2 (4) (EO8 = octaethylen glycol, EO2 = diethylene glycol) is obtained, in which the sodium cations are 7-fold coordinated within a disilane-bearing framework. The reaction of 2 with CsOTf failed, leading to recrystallization of anhydrous CsOTf. By means of DFT calculations it was shown that the disila-bearing ligands are burdened with negative hyperconjugation interactions between the silicon and the oxygen atoms, but the coordination by sufficiently hard cations can easily overcompensate the competing polarization. In contrast, soft Lewis acids barely share interactions with silicon-bonded oxygen atoms. All findings are consistent with observations made in solution according to 29Si NMR spectroscopical studies.

Exploring growth conditions and Eu2+ concentration effects for KSr2I5:Eu scintillator crystals II: Ø 25 mm crystals

Europium doped potassium strontium iodide is a very promising scintillator for national security applications due to its ease of growth and excellent scintillation properties. For this work the fast crystal growth and scintillation properties of 1-inch diameter single crystals of KSr2I5:Eu2+ (KSI:Eu) were investigated. We focused our efforts on optimizing the growth parameters required to produce one-inch diameter crystals without decreasing the previously reported fast pulling rate of 5 mm/h. Cracking was minimized by replacing the quartz ampoules with carbon coated quartz ampoules; thus, several crack free single crystals of KSI with varying Eu2+ concentrations were grown, including a Ø 1″ by 6″ long boule with 2.5% Eu.The maximum achievable performance of each crystal was measured using small 0.012 cm3 specimens. The volumetric dependencies of the light yield, energy resolution and decay time were evaluated using KSI:Eu 2% specimens with volumes ranging from 0.012 cm3 to 18 cm3. For large volumes (≥ 9 cm3), the performance was comparable to other high performing scintillators, with light yields up to 78,200 ph/MeV and energy resolutions as good as 3.2% at 662 keV. The initial version of a hermetic package has been developed, and the stability of the sealed crystal is promising.

High speed growth of SrI2 scintillator crystals by the EFG process

Strontium iodide (SrI2), an important new scintillator crystal having a high light yield and excellent energy resolution, was grown for the first time by the edge-defined film-fed (EFG) growth method. Using high purity starting materials and floating dies made of graphite, fused quartz or AlN, large cylindrical, planar or square cross-section single crystals (12–15mm across and >7cm long) were produced at growth rates up to 15mm/h, significantly faster than the current Bridgman growth technology. Details on the equipment used to grow this deliquescent material and on its growth behavior are given along with some discussion of crystalline quality.

Radioluminescence Properties of Europium Doped Strontium Aluminum Borate Glass

Recent topics of scintillation materials were development of halide single crystals which exhibit high energy resolution such as divalent Eu doped strontium iodide and novel solid neutron scintillators which contains high efficiency luminescent centers and Li-6 or B-10 ions which convert neutron to charged particles. One of the most traditional neutron scintillator is Ce doped Li silicate glass. On the other hand, Eu doped glass scintillators were not almost studied. We studied radioluminescence properties of Eu doped strontium aluminum borate glass (Eu 0.1% : 35 SrO – 15 Al2O3 – 50 B2O3) in order to obtain divalent Eu doped borate glass. As a result of X-ray excited luminescence, emission peaks were observed around 600 nm; they are originated from trivalent Eu. Emission peak was also observed around 400 nm; it might be originated from defect or divalent Eu. Detail of X-ray excited luminescence around 400 nm and Eu doping concentration dependence of radioluminescence spectra will be discussed on the conference.

Radiation damage of strontium iodide crystals due to irradiation by 137Cs gamma rays: A novel approach to altering nonproportionality

Strontium iodide doped with europium (SrI2:Eu2+) is a new scintillator being developed for use in high-energy astrophysical detectors with excellent energy resolution. Nonproportionality is the primary limiting factor to improving its energy resolution, although the physics of nonproportionality is not yet fully understood. In the past few years, co-dopants have been used to alter nonproportionality. By irradiating a SrI2:Eu2+ sample with a 2255 Ci 137Cs source, we explore both the crystal's potential for space-based applications in a radiation environment and this new method of altering nonproportionality. At ~6200Gy irradiation, a drop of 7.8% at 700nm and a drop of 14.1% at 450nm were seen in the transmission spectrum. Nonproportionality was also reduced after irradiation, shifting from 87% to 101% of the theoretical light yield at 32.1keV, while the 4.7keV peak decreased 40% closer to its theoretical value. We propose a novel method of altering the nonproportionality of scintillators, using radiation-induced F-centers in place of co-dopants.