Advanced Scintillators Research Articles

Impurity-enhanced core valence luminescence via Zn-doping in cesium magnesium chlorides

Scintillators with faster timing capabilities are currently in high demand for use in radiation detection systems in the fields of nuclear and medical physics. The limited number of suitable materials that meet the performance criteria of next generation detection systems presents an opportunity for discovery of new fast scintillator materials. In this work, the effects of doping several ultrafast core-valence luminescent (CVL) scintillators with divalent Zn is explored. Three compounds are investigated – CsMgCl3, Cs2MgCl4, and Cs3MgCl5 – and single crystals of each doped with 5 mol% Zn are grown via the Bridgman method. Additionally, mixing across the full range of concentrations (from 0 % to 100 % Zn) is explored in the Cs2Mg1-xZnxCl4 and Cs3Mg1-xZnxCl5 systems. For low concentrations of Zn, light yields of all three compounds are enhanced (by up to ∼60 %) compared to the pure crystals, achieving what we believe to be the brightest known CVL, CsMgCl3:Zn 5 % (3400 ± 170 ph/MeV light yield). More importantly, Zn doping does not affect the ultrafast timing properties, with each composition maintaining a single-component decay time around 1–3 ns. A sub-100 ps coincidence time resolution (CTR) is also achieved with CsMgCl3:Zn 5 %. The results of this work reveal a new avenue towards obtaining brighter CVL materials, which could open up possibilities for more advanced ultrafast scintillators to be discovered moving forward.

Reducing Luminescence Intensity and Suppressing Irradiation‐induced Darkening of Bi4Ge3O12 by Ce‐doping for Radiation Detection

AbstractDue to its short radiation length, moderate light output (8000‐9000 photons/MeV), high density (7.13 g cm−3), and non‐hygroscopicity, etc., Bi4Ge3O12 (BGO) material has been widely utilized as an advanced scintillator for irradiation detection. However, pure BGO cannot meet the requirements for future physics experiments and state‐of‐art industrial facilities coupled with a silicon photomultiplier (SiPM) due to its slow response time, poor radiation resistance, and excessive light output. Herein, a Ce‐doping strategy is reported for efficiently improving the overall performance (e.g., irradiation resistance, decay time, radioluminescence, and light output) of BGO that can be expectedly applied in future high energy physics detection. Ce‐doped BGO (BGO:Ce) displays higher radiation resistance ability under 10 h UV irradiation (97% of original) and a faster fluorescence lifetime (269 ns), superior to pure BGO. Furthermore, BGO:Ce shows ≈30% luminescence intensity of pure BGO, well eliminating the oversaturation of SiPM coupled with scintillation detectors. Theoretical calculations imply that an intense competition between electron or hole traps and Ce ions (Ce3+, Ce4+) can effectively reduce the concentration of color centers, thus enhancing irradiation resistance ability.

Characterization of large diameter dual-mode cerium-doped Tl2LiYCl6 advanced scintillator

In this paper we are reporting on the progress and scale up of the Cerium-doped Tl2LiYCl6 (TLYC) scintillator. The boules up to 2-inch in diameter were grown by the Bridgman method at Fisk University. The lapped and polished samples were characterized for their scintillation properties including gamma-neutron dual mode detection. The 1.5-inch diameter samples demonstrated the energy resolution as good as 4.5% (FWHM) at 662 keV. The neutron peak due to 6Li(n, α) reaction was observed at 1.8 MeV gamma equivalent energy. Gamma-neutron pulse shape discrimination (PSD) was demonstrated with the Figure-of-Merit (FOM) of 1.8. The hermetically encapsulated samples were also evaluated for their radiation hardness with irradiation up to 1 Mrad.

Structural tailoring of p-terphenyl scaffold: Towards advanced plastic scintillator

A comprehensive series of fifteen p-terphenyl derivatives has been designed and prepared using facile synthetic approaches (Suzuki-Miyaura and Friedel-Crafts reactions). Various alkyl, alkoxy or trifluoromethyl groups have been attached to p-terphenyl to gain both symmetrical and unsymmetrical derivatives. Symmetry breaking accounts for improved solubility of mono-substituted derivatives. Thermal analysis revealed a reversible formation of several crystalline phases and very high thermal robustness. Reduction and oxidation of the parent p-terphenyl π-system affected by the electronic and steric effects of the substituents were recorded by cyclic voltammetry. When compared to parent p-terphenyl, a narrowed HOMO–LUMO gap has been measured/calculated for most of the prepared derivatives. The absorption and emission maxima ranged from 286 to 293 and 341–360 nm, respectively. The latter is affected by the substitution more significantly, the fluorescence quantum yields are within the range of 0.52–0.75. Stokes shifts up to 6400 cm−1 were measured pointing to a large structural rearrangement (planarization) upon excitation. PTP derivatives were further used as primary and secondary luminophores for scintillation. 4-Methyl-p-terphenyl proved to be a superior luminophore with a straightforward synthesis, easy isolation, large solubility and excellent luminescence characteristic. Based on this derivative, a plastic scintillator has been manufactured that showed superior performance as compared to standard and widely used unsubstituted p-terphenyl. Thus, a relatively minor structural change (appending single methyl group) altered scintillation properties significantly.

Accelerator Technology for Well Logging: Advances, Challenges, and Opportunities

Accelerators have been integral to subsurface probing for decades. Tools with deuterium-tritium (D-T) generators and scintillators utilizing gamma rays from thermal neutron capture, inelastic scattering, and activation are routine in cased-hole logging tools for reservoir and well monitoring to locate and quantify remaining hydrocarbons prior to initiating secondary or tertiary production. X-ray and neutron generators field-tested to, respectively, replace 137Cs and americium-beryllium (Am-Be) source tools that measure two bulk parameters, formation density and neutron porosity critical for initial characterization of formations, have yielded mixed results. D-T generator-based spectroscopy tools with advanced scintillators that can record both inelastic and capture n-gamma spectra, faster and with much better energy resolution, to provide a more complete mineralogy appear poised to replace Am-Be–based mineralogy tools. In view of their ability to measure both bulk and spectral parameters, accelerator-based nuclear methods appear attractive to extract additional geological information needed to transition to a low-carbon energy future. The paper discusses the current state of application of accelerator-based subsurface probing techniques, notes their potential for nonpetroleum applications, and concludes by briefly exploring technology advances that could significantly advance the state of the art.

Ce 3+:Lu 3Al 5O 12–Al 2O 3 optical nanoceramic scintillators elaborated via a low-temperature glass crystallization route

Transparent Ce:lutetium aluminum garnet (Ce:Lu₃Al₅O₁₂, Ce:LuAG) ceramics have been regarded as potential scintillator materials due to their relatively high density and atomic number (<i>Z</i>_eff). However, the current Ce:LuAG ceramics exhibit a light yield much lower than the expected theoretical value due to the inevitable presence of Lu_Al antisite defects at high sintering temperatures. This work demonstrates a low-temperature (1100 ℃) synthetic strategy for elaborating transparent LuAG–Al₂O₃ nanoceramics through the crystallization of 72 mol% Al₂O₃–28 mol% Lu₂O₃ (ALu28) bulk glass. The biphasic nanostructure composed of LuAG and Al₂O₃ nanocrystals makes up the whole ceramic materials. Most of Al₂O₃ is distributed among LuAG grains, and the rest is present inside the LuAG grains. Fully dense biphasic LuAG–Al₂O₃ nanoceramics are highly transparent from the visible region to mid-infrared (MIR) region, and particularly the transmittance reaches 82% at 780 nm. Moreover, Lu_Al antisite defect-related centers are completely undetectable in X-ray excited luminescence (XEL) spectra of Ce:LuAG–Al₂O₃ nanoceramics with 0.3–1.0 at% Ce. The light yield of 0.3 at% Ce:LuAG–Al₂O₃ nanoceramics is estimated to be 20,000 ph/MeV with short 1 μs shaping time, which is far superior to that of commercial Bi₄Ge₃O₁₂ (BGO) single crystals. These results show that a low-temperature glass crystallization route provides an alternative approach for eliminating the antisite defects in LuAG-based ceramics, and is promising to produce garnet-based ceramic materials with excellent properties, thereby meeting the demands of advanced scintillation applications.

A high-speed radiation imaging system based on liquid scintillator filled capillary arrays.

A high-speed radiation imaging system based on an image converter of liquid scintillator filled capillary arrays has been developed, which is sensitive to x rays, gamma rays, and neutrons. This imaging system has advantages of both high spatial resolution and high sensitivity because increasing the thickness of the image converter only leads to little deterioration on imaging resolution. The capillary arrays have dimensions of 150mm diameter and 50mm thickness, with 100 µm diameter of each capillary. The fluorescence decay time of the filled liquid scintillator based on the mixture of p-xylene and 2,5-diphenyloxazole has been evaluated to be ∼3ns with the single photon method under the gamma ray excitation. The spatial resolution has been experimentally evaluated to be about 1.15 and 0.6mm, under excitation of x rays and neutrons, respectively. The imaging system has been applied for diagnosing the dynamic x-ray spot generated by the rod pinch. Two frames in single shot with 15ns temporal resolution and 20ns inter-frame separation time have been obtained, which show the spatiotemporal distribution of the electrons bombarding the tungsten rod, indicating the ability of this imaging system in diagnosing dynamic radiation objects. In addition, the technique of capillary arrays provides a promising path for applications of advanced liquid scintillators in the field of radiation imaging.

Gamma-Ray Interaction of Selected Inorganic Scintillators Used in HEP Experiments

We attempted to study gamma-ray attenuation and sensing properties of conventional and modern inorganic scintillators being employed in the high energy physics (HEP) experiments. The mass attenuation coefficient (μm ), effective atomic number (Zeff ) and mean free path (mfp)were theoretically evaluated for the conventional scintillators materials such as CsI and NaI (Tl) and compared with advanced scintillator materials: PWO, PbF2, and BGO along with rare earth elements based scintillators such as LYSO:Ce, LuAG:Ce, BaF2:Y which have been proposed for applications in the future HEP experiments. Thegamma-ray attenuation parameters are analyzed within the framework of online software toolkit ‘py-MULBF’ over wide photon energy range from 0.015 MeV to 15 MeV.Variationof μm (and, Zeff ) with photon energy follows a trend similar for most of the inorganic scintillator materialsinvestigated here.CsI, however, maintained almost same effective atomic number value with respect to photon energy which signifies that CsI may be suitable for specific gamma-ray detection and sensing applications. Lead-based scintillator materials such as PbF2, PWO along with high-Z BGO are observed to exhibit better radiation attenuation capabilities.

Balloon flight test of a CeBr3 detector with silicon photomultiplier readout

Recent advances in silicon photomultiplier (SiPM) technology and new scintillator materials allow for the creation of compact high-performance gamma-ray detectors which can be deployed on small low-cost satellites. A small number of such satellites can provide full sky coverage and complement, or in some cases replace the existing gamma-ray missions in detection of transient gamma-ray events. The aim of this study is to test gamma-ray detection using a novel commercially available CeBr3 scintillator combined with SiPM readout in a near-space environment and inform further technology development for a future space mission. A prototype gamma-ray detector was built using a CeBr3 scintillator and an array of 16 J-Series SiPMs by ON Semiconductor. SiPM readout was performed using SIPHRA, a radiation-tolerant low-power integrated circuit developed by IDEAS. The detector was flown as a piggyback payload on the Advanced Scintillator Compton Telescope balloon flight from Columbia Scientific Balloon Facility. The payload included the detector, a Raspberry Pi on-board computer, a custom power supply board, temperature and pressure sensors, a Global Navigation Satellite System receiver and a satellite modem. The balloon delivered the detector to 37 km altitude where its detection capabilities and readout were tested in the radiation-intense near-space environment. The detector demonstrated continuous operation during the 8-hour flight and after the landing. It performed spectral measurements in an energy range of 100 keV to 8 MeV and observed the 511 keV gamma-ray line arising from positron annihilation in the atmosphere with full width half maximum of 6.8%. During ascent and descent, the detector count rate peaked at an altitude of 16 km corresponding to the point of maximum radiation intensity in the atmosphere. Despite several engineering issues discovered after the flight test, the results of this study confirm the feasibility of using CeBr3 scintillator, SiPMs, and SIPHRA in future space missions.

Gallium Concentration Optimisation of Gallium Doped Zinc Oxide for Improvement of Optical Properties

Abstract The near-band luminescence of doped ZnO is promising for advanced scintillators; however, the dopant type and concentration effects require a detailed study. Undoped and Ga-doped ZnO nanopowders were prepared by a microwave-assisted solvothermal method and the gallium concentration effect on luminescence properties was studied. The near-band luminescence peak position dependence on gallium concentration was observed. Near-band luminescence intensity versus defect luminescence intensity ratio was explored for different gallium concentrations and the optimal value was determined. Samples were prepared with dopant concentrations between 0.2 and 1.5 at%, XRD analysis confirmed that samples contained only zinc oxide hexagonal wurtzite phase. The results of the research showed that ZnO:Ga containing 0.9 at.% gallium was promising for scintillators.

Influence of field conditions on quantitative analysis of single crystal thorium dioxide by atom probe tomography

Atom probe tomography (APT), a 3D microscopy technique, has great potential to reveal atomic scale compositional variations, such as those associated with irradiation damage. However, obtaining accurate compositional quantification by APT for high bandgap materials is a longstanding challenge, given the sensitivity to field evaporation parameters and inconsistent behaviors across different oxides. This study investigates the influence of APT laser energy and specimen base temperature on compositional accuracy in single crystal thoria (ThO2). ThO2 has a broad range of applications, including advanced nuclear fuels, sensors, lasers and scintillators, electrodes, catalysis, and photonics and optoelectronics. The expected stoichiometry of ThO2 is achieved at APT base temperature of 24 K and laser energy of 100 pJ. To overcome mass resolution limitations associated with significant thermal tails, Bayesian methods are applied to deconvolute ion identity within the mass spectra. This approach affirms that the parameters chosen are appropriate for APT analysis of ThO2.

Advanced algorithms for signal processing scintillation gamma ray detectors at high counting rates

Gamma ray spectrometry measurements at high detector counting rates (on the order of 107 s−1 and higher) are relevant for high-temperature plasma diagnostics for existing tokamaks and during the development of gamma ray diagnostic systems for the ITER tokamak under construction. At high loads, to obtain spectra without distortion and with a small amount of dead time, it is necessary to use advanced scintillation detector signal processing methods, which can resolve superimposed pulses. Two algorithms that can be used for digital signal processing of scintillation gamma ray detectors with many piled-up pulses are considered in this article, the fitting and deconvolution methods. These algorithms are compared with both one another and two less sophisticated pulse-height analysis algorithms (maximum height and total sum under the peak) in applications that process model and measured signals. Baseline detection algorithms are also considered, which are necessary when processing signals from detectors. The algorithms are applied to LaBr3(Ce) detector signal processing. For the modeled signals, the best results in terms of the number of resolved events and energy resolution at counting rates up to 2 × 107 s−1 of the LaBr3(Ce) detector are demonstrated by the fitting method. In the real gamma ray measurements at a loading of 5.1 106 s−1, the deconvolution method demonstrated the best energy resolution.

Prospects for THEIA: an advanced liquid scintillator neutrino experiment

THEIA is a proposed large-scale neutrino experiment based on advanced liquid scintillator and readout by high-quantum efficiency and fast photosensors. In order to combine the advantages of water Cherenkov detectors (i.e. large mass, direction reconstruction and low cost) with the ones of liquid scintillator (high light yield, low threshold) THEIA will deploy a Water-based Liquid Scintillator, which is currently at the center of an active R&D program. This detector concept has the potential to pursue a broad physics program that is summarized in this contribution. As a long baseline experiment installed at Homestake, THEIA will be complementary to the forthcoming DUNE experiment for the determination of the neutrino mass hierarchy and of the CP phase. At the same time, the low energy threshold and efficient neutron tagging makes THEIA an excellent detector for solar and supernova neutrinos measurements as well as for the search of neutrinoless ββ-decay and of other rare phenomena.

Liquid phase epitaxy growth of high-performance composite scintillators based on single crystalline films and crystals of LuAG

Top – Scheme of the composite scintillator for registration of α-particles and γ-quanta. Bottom – Samples of the LuAG:Ce SCF/LuAG:Sc SC (a) and LuAG:Pr SCF/LuAG:Sc SC (b) composite scintillators prepared using the liquid phase epitaxy growth method.

Research on Efficient Fast Scintillators: Evidence and X‐Ray Absorption Near Edge Spectroscopy Characterization of Ce4+ in Ce3+, Mg2+‐Co‐Doped Gd3Al2Ga3O12 Garnet Crystal

Herein, the most advanced oxide scintillator Ce3+, Mg2+‐co‐doped Gd3Al2Ga3O12 (GAGG) garnet host, grown using the Czochralski method is reported. The charge transfer absorption band in UV, such as in other Ce3+, Mg2+‐co‐doped oxides, reveals the creation of stable Ce4+ oxidation state, in addition to the usual Ce3+ one, admitted as responsible of the scintillation mechanism improvement displayed by this garnet. Strangely, the confirmation of quantitative values of Ce4+ concentration has never been done, and the goal is mainly focused on the presence of Ce4+ and the evaluation of the Ce3+/Ce4+ ratio measured by X‐ray absorption near edge spectroscopy (XANES) spectroscopy at the Ce LIII threshold of the European Synchrotron Radiation Facility (ESRF). This result is compared with those obtained for Ce3+, Mg2+‐co‐doped Lu3Al5O12 (LuAG) and, also, in garnets without any Mg2+ ions such as Ce3+‐doped GAGG, Ce3+‐doped LuAG, and Ce3+‐doped YAG. The role of Li+ ion in place of Mg2+ one is also considered in Ce3+, Li+‐co‐doped LuAG single crystal.

Comprehending the role of trap centers and host energy transfers in excitation density dependent kinetics of Ce doped Gd3Ga3Al2O12scintillator; an unresolved scintillation characteristic

Single crystal of Ce doped Gd3Ga3Al2O12 is one of the most studied advanced scintillators currently. The scintillation kinetics has been investigated with different excitations. The higher excitation density of alpha particles quenches the scintillation light yield but on the contrary the decay curve gets accelerated with gamma rays unlike that have been typically observed for conventionally used halide scintillators. In view of resolving this unusual behavior, a thorough investigation has been first time performed by carrying out systematic experiments on temperature dependent scintillation properties with gamma and alpha irradiation. The dependence of light yield for both radiations behaves differently with temperature with a notable early onset of quenching for charged particles. All three decay components also behave differently with temperature to indicate the various mechanisms governing the relaxation of excited charged carriers. At some temperatures the decay time components indeed behave in the similar manner as measured for halide crystals. The maximum difference in decay components carrying major amplitude occurs close to room temperatures leading to better discrimination ability. A strong correlation with thermo-luminescence properties has been observed to investigate the role of defect structure. A comprehensive model based on the prominent role of charged carriers released from trap centers along with the energy transfer and migration via Gd sub-lattice in governing the scintillation properties has been convincingly presented. It has demonstrated precisely the unusual behavior of this material but can be extended more considerably to describe various properties of other scintillators as well.

Advanced scintillators for fast-timing applications

Gamma spectroscopy has been recast by a new generation of inorganic scintillators, mostly halide compounds, with large effective atomic number, excellent timing properties and a good energy resolution. The most prominent example is LaBr3(Ce), commercially available for more than a decade. The impact of LaBr3(Ce) in fast-timing experiments dedicated to measure nuclear state lifetimes has been tremendous. In fact, it has been the key player in the development of fast-timing with mixed arrays of HPGe detectors and fast scintillators. In this contribution we discuss the main parameters affecting the precision of timing measurements. We describe the evaluation of a newly-available LaBr3(Ce+Sr) crystal for fast-timing applications, and compare the time and energy resolutions to a well-established LaBr3(Ce) of the same size and shape. The measurements are performed using a fully-digital signal processing data acquisition system, which has been proven to yield even better results than standard analog acquisition systems.

Novel All-Solid-State Composite Scintillators Based on the Epitaxial Structures of LuAG Garnet Doped With Pr, Sc, and Ce Ions

This paper presents our achievement in the development of new types of advanced composite scintillators (CSs) based on the single crystalline films (SCFs) of Lu3Al5O12 (LuAG) garnet, doped with Pr3+ and Sc3+ ions, and substrate from single crystals (SCs) of Ce3+-doped LuAG using the technology of liquid phase epitaxy. We show the possibility of the simultaneous registration of $\alpha$ -particles and $\gamma$ -quanta by means of separation of the decay kinetics of SCF and crystal parts of such CSs. Namely, the significant differences in the scintillation decay kinetics of LuAG:Pr SCF/LuAG:Ce SC and LuAG:Sc SCF/LuAG:Ce SC CSs under excitation by $\alpha$ -particles of 241Am (5.5 MeV) source and $\gamma$ -quanta of 137Cs (662 keV) source are observed. Thus, such types of CSs can be successfully applied for separation of the signals coming from their film and crystal parts at the registration of the mixed radiation fluxes of $\alpha$ -particles and $\gamma$ -quanta.

Composite scintillators based on the crystals and single crystalline films of LuAG garnet doped with Ce3+, Pr3+ and Sc3+ ions

This work is devoted to the development of new types of advanced composite scintillators based on the single crystalline films (SCFs) of Lu3Al5O12 (LuAG) garnet, doped with Pr3+ and Sc3+ ions, and substrate from single crystals (SCs) of Ce3+ doped LuAG using the technology of liquid phase epitaxy (LPE). We show the possibility of the simultaneous registration of α-particles and γ-quanta by means of separation of the decay kinetics of SCF and crystal parts of such composite scintillators. Namely, the significant differences in the pulse height spectra and the scintillation decay kinetics of LuAG:Pr SCF/LuAG:Ce SC and LuAG:Sc SCF/LuAG:Ce SC composite scintillators under excitation by α–particles of 241Am (5.5 MeV) source and γ-quanta of 137Cs (662 keV) source are observed. For these reasons, such types of composite scintillators can be applied for separation of the signals coming from their film and crystal parts at the registration of the mixed radiation fluxes of α-particles and γ-quanta.

TRIMAGE: A dedicated trimodality (PET/MR/EEG) imaging tool for schizophrenia

Simultaneous PET/MR/EEG (Positron Emission Tomography – Magnetic Resonance – Electroencephalography), a new tool for the investigation of neuronal networks in the human brain, is presented here within the framework of the European Union Project TRIMAGE. The trimodal, cost-effective PET/MR/EEG imaging tool makes use of cutting edge technology both in PET and in MR fields. A novel type of magnet (1.5T, non-cryogenic) has been built together with a PET scanner that makes use of the most advanced photodetectors (i.e., SiPM matrices), scintillators matrices (LYSO) and digital electronics. The combined PET/MR/EEG system is dedicated to brain imaging and has an inner diameter of 260 mm and an axial Field-of-View of 160 mm.It enables the acquisition and assessment of molecular metabolic information with high spatial and temporal resolution in a given brain simultaneously. The dopaminergic system and the glutamatergic system in schizophrenic patients are investigated via PET, the same physiological/pathophysiological conditions with regard to functional connectivity, via fMRI, and its electrophysiological signature via EEG. In addition to basic neuroscience questions addressing neurovascular-metabolic coupling, this new methodology lays the foundation for individual physiological and pathological fingerprints for a wide research field addressing healthy aging, gender effects, plasticity and different psychiatric and neurological diseases.The preliminary performances of two components of the imaging tool (PET and MR) are discussed. Initial results of the search of possible candidates for suitable schizophrenia biomarkers are also presented as obtained with PET/MR systems available to the collaboration.