Fast Scintillation Materials Research Articles

Novel compositionally disordered (Pb,Sr)WO4 single-crystalline scintillation material for X- and gamma-ray scanners

Heavy, bright, and fast single-crystalline scintillation material (Pb,Sr)WO4 was produced and characterized for the first time. Incongruently melted material was obtained by the solution-melt method under the conditions of spontaneous crystallization. It has a density of 7.3 g/cm3 and an effective charge of Zeff = 71. The scintillation kinetics are characterized by a decay constant of 490 ns, while the light yield of scintillation is measured to be 13 500 ph/MeV, both at room temperature. A fabrication of the new low-temperature melting single crystalline tungstate family’s material opens the door for better and cheaper scintillators for X-ray and γ-ray detectors, in particular for radiographic scanners and medical imaging devices.

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.

Customizing the luminescent properties of compositionally disordered ceramics (Gd, Y, Yb, Tb, Ce)3Al2Ga3O12: From an ultra-fast scintillator to bright, wide-spectrum phosphor

A series of (Gd, Y, Yb, Tb, Ce)3Al2Ga3O12 compositionally disordered compounds with a garnet structure were prepared in the form of ceramics by sintering in oxygen at 1650 °C for 2 h and studied for the luminescent properties and interaction of ions entering the matrix host. The luminescence features of Ce3+ ions were found to be strongly dependent on the Yb concentration. Photoluminescence and scintillation kinetics are characterized by subnanosecond kinetics when the Yb index in the compound exceeds X = 0.3. It opens an opportunity to create an extremely fast and dense scintillation material emitting in a visible range. A further decrease in the Yb index in the compound leads to an increase in the intensity of Yb3+ infrared (IR) emission, whereas Ce3+ and Tb3+ ions contribute to the luminosity of the material by overlapping intra- and intereconfiguration luminescence bands in the spectral range of 300–700 nm. This finding opens an opportunity to create converter materials tolerant to the corpuscular radiation of isotope sources, providing a high efficiency of electric current production when coupled with a silicon photovoltaic element. The compounds were engineered at the nanoscale level, providing control over electronic excitation transfer between luminescent ions.

Fast response 4f15d1→4f2 emission and host-to-impurity energy transfer in Pr3+ doped Na3LuSi3O9 double salt silicate

Understanding of host-to-impurity energy transfer process is crucial for the development of efficient and fast response scintillator materials. In this work, Pr3+ doped Na3LuSi3O9 (NLS) double salt silicate has been successfully synthesized using a high temperature solid-state reaction method and further comprehensively characterized by means of XRD measurements, crystal structure refinement, luminescence spectroscopic and time-domain study upon VUV-UV and X-ray synchrotron excitation, and thermally stimulated luminescence (TSL) study. Based on these results a model of host to Pr3+ 4f15d1 and 4f2 has been proposed. It has been demonstrated that NLS:Pr3+ has a good potential for fast response scintillator applications due to the presence of an efficient energy transfer from host electronic excitations to Pr3+ 4f15d1 states. The Pr3+ 4f15d1→4f2 emission reveals a good thermal stability and is characterized by a lifetime of about 16 ns. Upon pulse X-ray excitation the main fast decay component is accompanied by slower one with lifetime of about 64 ns that is ascribed to the presence of shallow traps which retrap carriers and cause appearance of delayed recombination. Parameters for the corresponding traps have been calculated based on the TSL glow curve analysis.

Charge Transfer and Charge Trapping Processes in Ca- or Al-Co-doped Lu2SiO5 and Lu2Si2O7 Scintillators Activated by Pr3+ or Ce3+ Ions.

Lutetium oxyorthosilicate Lu2SiO5 (LSO) and pyrosilicate Lu2Si2O7 (LPS) activated by Ce3+ or Pr3+ are known to be effective and fast scintillation materials for the detection of X-rays and γ-rays. Their performances can be further improved by co-doping with aliovalent ions. Herein, we investigate the Ce3+(Pr3+) → Ce4+(Pr4+) conversion and the formation of lattice defects stimulated by co-doping with Ca2+ and Al3+ in LSO and LPS powders prepared by the solid-state reaction process. The materials were studied by electron paramagnetic resonance (EPR), radioluminescence spectroscopy, and thermally stimulated luminescence (TSL), and scintillation decays were measured. EPR measurements of both LSO:Ce and LPS:Ce showed effective Ce3+ → Ce4+ conversions stimulated by Ca2+ co-doping, while the effect of Al3+ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr3+ → Pr4+ conversion was not detected by EPR, suggesting that the charge compensation of Al3+ and Ca2+ ions is realized via other impurities and/or lattice defects. X-ray irradiation of LPS creates hole centers attributed to a hole trapped in an oxygen ion in the neighborhood of Al3+ and Ca2+. These hole centers contribute to an intense TSL glow peak at 450-470 K. In contrast to LPS, only weak TSL peaks are detected in LSO and no hole centers are visible via EPR. The scintillation decay curves of both LSO and LPS show a bi-exponential decay with fast and slow component decay times of 10-13 ns and 30-36 ns, respectively. The decay time of the fast component shows a small (6-8%) decrease due to co-doping.

Timing advances of commercial divalent-ion co-doped LYSO:Ce and SiPMs in sub-100 ps time-of-flight positron emission tomography

Objective. Together with novel photodetector technologies and emerging electronic front-end designs, scintillator material research is one of the key aspects to obtain ultra-fast timing in time-of-flight positron emission tomography (TOF-PET). In the late 1990s, Cerium-doped lutetium–yttrium oxyorthosilicate (LYSO:Ce) has been established as the state-of-the-art PET scintillator due to its fast decay time, high light yield and high stopping power. It has been shown that co-doping with divalent ions, such as Ca 2+ and Mg 2+, is beneficial for its scintillation characteristics and timing performance. Therefore, this work aims to identify a fast scintillation material to combine it with novel photosensor technologies to push the state of the art in TOF-PET. Approach. This study evaluates commercially available LYSO:Ce,Ca and LYSO:Ce,Mg samples manufactured by Taiwan Applied Crystal Co., LTD regarding their rise and decay times as well as their coincidence time resolution (CTR) with both ultra-fast high-frequency (HF) readout and commercially available readout electronics, i.e. the TOFPET2 ASIC. Main results. The co-doped samples exhibit state-of-the-art rise times of on average 60 ps and effective decay times of on average 35 ns. Using the latest technological improvements made on NUV-MT SiPMs by Fondazione Bruno Kessler and Broadcom Inc., a 3 × 3 × 19 mm3 LYSO:Ce,Ca crystal achieves a CTR of 95 ps (FWHM) with ultra-fast HF readout and 157 ps (FWHM) with the system-applicable TOFPET2 ASIC. Evaluating the timing limits of the scintillation material, we even show a CTR of 56 ps (FWHM) for small 2 × 2 × 3 mm3 pixels. A complete overview of the timing performance obtained with different coatings (Teflon, BaSO4) and different crystal sizes coupled to standard Broadcom AFBR-S4N33C013 SiPMs will be presented and discussed. Significance. This work thoroughly evaluates commercially available co-doped LYSO:Ce crystals and, in combination with novel NUV-MT SiPMs, shows a TOF performance that significantly exceeds the current state of the art.

Design of a High-Speed Neutron Imager Using a Boron-Loaded Organic Glass Scintillator

Upgrades to the Spallation Neutron Source at Oak Ridge National Laboratory will provide a second target station and an increased neutron flux, which will offer a more powerful tool for neutron reflectometry. To fully utilize the higher neutron flux, a high-speed, neutron-imaging device (an imaging plane) specifically for reflectometry is required. The neutron imaging plane requires a detection efficiency of 60% for 2 Å neutrons for event rates exceeding 2 Mcps/cm2 with less than 10% dead time. A novel organic glass scintillator material loaded with a boron compound demonstrated good neutron sensitivity. Simulations show that the detection efficiency for thermal neutrons can reach 60% with a 500 μm thickness, if the glass is loaded with 99% enriched 10B compound at 10%wt. A lower concentration of 95% enrichment at 5%wt loading can provide 60% efficiency with a thickness slightly above 1mm. The decay time of the scintillator is less than 100 ns, providing a fast response for high rate counting. The instrument design is based on detecting the neutron with a fast scintillation material and integrating silicon photomultipliers with high-speed digital electronics. Traditional pulse sampling using a high-speed analog to digital converter to conduct pulse shape discrimination is not viable for imaging, and a new technique has been formulated for this material using a time over threshold method to isolate neutrons from gamma ray interactions. The gamma-neutron peak separation is greater than 2 sigma, and with a thin scintillator, the gamma ray rejection per detected neutron should meet the design specification of 10-6. Using the time over threshold method, the digital information to be processed by a interfacing ADC is reduced allowing for readout per SiPM, providing a position resolution close to 1 mm.

Upgrade and absolute calibration of the JET scintillator-based fast-ion loss detector

The JET FILD is a scintillator-based Fast-ion Loss Detector optimized to measure fusion-born alpha-particle losses. This work covers its upgrade and absolute calibration in preparation for the following JET DT experiments. A fast scintillator material (TG-Green) has been installed in the JET FILD. A heater jacket is installed around the fiber bundle, responsible for transmitting the light from the scintillator plate, to anneal the fiber obscuring due to neutron damage. The JET FILD has been upgraded with a 1 Mpx camera and 2MHz photomultiplier data acquisition hardware. Full-orbit simulations give an estimate of the shading effects on the scintillator plate of the first wall structures and provide a synthetic signal of the JET FILD. A detector instrument function enables absolute values of fast-ion losses using calibration factors. The calibration factors are made available in a shot-to-shot basis for the characterized species and energies and with corrections for the diagnostic conditions. The fast acquisition system sets the Nyquist frequency (1MHz) above the typical mode frequencies (≈102kHz), thus making it possible to identify MHD-induced fast-ion losses.

Impulse response measurements of fast scintillator-based current mode detectors

Experimental measurements were performed to characterize the impulse response of seven different gamma ray detector prototypes being considered to be fielded as a current mode diagnostic for neutron-diagnosed subcritical experiments at the Nevada National Security Site (NNSS). For such experiments, the impulse response of the fielded detector is required to have a full-width half-maximum (FWHM) of approximately 5 ns or less and a low amplitude tail. Each of the detector prototypes evaluated in this work were selected based on the potential to meet this performance requirement. An impulse of bremsstrahlung x-rays created from 2 MeV electrons from the NNSS’s Transformational Diagnostics and Imaging, Los Alamos, linear accelerator was measured with each detector. The measured impulse response was evaluated for each detector configuration. A comparison of these impulse responses revealed a relationship between fast timing performance and scintillator material, geometry, surface reflectivity conditions, and photomultiplier tube (PMT) selection. The detector configuration yielding an impulse response with the shortest FWHM of 3.82 ± 0.11 ns and possessing a low amplitude tail was a 5-inch (12.7-cm) diameter, 5-inch (12.7-cm) height cylindrical EJ-399-17-VI liquid scintillator in a black-painted housing coupled to an Adit D798B 5-inch (12.7-cm) PMT by means of a 0.079-inch (0.2-cm) EJ-560 optical coupling pad.

Luminescence and scintillation properties of Cs2ZnCl4 and Cs3ZnCl5

Fast scintillation materials based on the ternary halide crystals of Cs2ZnCl4 and Cs3ZnCl5 were synthesized. Under X-ray irradiation, an emission band at 310 nm with shoulders at 260 and 410 nm was observed for Cs2ZnCl4, and emission bands at 240, 290, and 390 nm were observed for Cs3ZnCl5. The observed bands were primarily attributable to Auger-free luminescence (AFL). In the temporal scintillation profiles, scintillation decay time constants of 1.7 and 1.1 ns were found for Cs2ZnCl4 and Cs3ZnCl5, respectively. These fast components are attributed to AFL and constituted greater than 88% of the total scintillation amount. On the basis of the pulse height spectra, the light yields of Cs2ZnCl4 and Cs3ZnCl5 were estimated to be 1280 and 440 photons MeV−1, respectively. The light yield of the fast component of Cs2ZnCl4 was slightly lower than that of BaF2, which is a commercially available fast scintillator exhibiting AFL.

Luminescence characteristics of Cs2BaCl4

Fast scintillation material based on the ternary halide crystal of Cs2BaCl4 was synthesized. Under X-ray excitation, bands ascribed to STEs and AFL were observed. Cs2BaCl4 had a low scintillation decay time constant of 1.2 ns, whose proportion was approximately 70% of the total scintillation amount. The light yield of Cs2BaCl4 was estimated through measuring the gamma-ray-excited pulse height spectra. Cs2BaCl4 had a total light yield of 2400 photons/MeV. Considering the proportion of the fast component was 70% of the total scintillation amount, the fast component light yield was approximately 1700 photons/MeV, which is larger than that of BaF2.

Comparative study on fluorescence decay time of doped ZnO crystals under α and β excitation

To acquire the direct time response of ZnO crystals to high energy particles, a dual-channels single photon correlation (DCSPC) system based on the measurement of the autocorrelation function of the fluoresce temporal profile was employed. The measuring resolution of the DCSPC system calibrated by Cerenkov luminescence is 46 ps. With this DCSPC system, the fast decay time constants of ZnO:Ga, ZnO:In and ZnO:Sc under charged particle alpha and beta excitation were successfully measured, which are 1.56 ns, 0.48 ns, 0.12 ns, and 1.11 ns, 0.40 ns, 0.10 ns, respectively . For all the three samples, it is found that the decay time constants under beta excitation are faster than those under alpha excitation, indicating that ZnO crystal is a fast scintillation material with pulse shape discrimination (PSD) ability. This would be applied in selective detection of mixed radiation field, particularly where high counting rate is required.

A liquid VI scintillator cell for fast-gated neutron imaging.

The design of a new fast-gated neutron imaging system for the National Ignition Facility with much stricter timing constraints than a previous system has prompted the search for a fast scintillator material that can be used in imaging. A novel imaging cell based on Liquid VI has recently been developed with Eljen Technology and characterized at the Special Technologies Laboratory and the Los Alamos Neutron Science Center. The results show superior timing characteristics and spatial resolution, and sufficient light production for the new system compared to fast plastic scintillators previously used in neutron imaging. While the primary application is in inertial confinement fusion diagnostics, the imaging cell can be used in any fast-gated imaging application where timing characteristics and spatial resolution are of concern.

Effects of atmosphere and temperature on luminescence property of YAG:Ce synthesized by co-precipitation method

Ce-doped yttrium aluminum garnet (YAG)-based crystal powders were synthesized using a co-precipitation method. The effects of the sintering atmosphere and temperature on the luminescence property were investigated using the photoluminescence (PL) and cathodoluminescence (CL) spectroscopy along with X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS). The PL and CL results showed that YAG:Ce samples sintered in an inert atmosphere at high temperatures had a higher luminescence intensity around 550 nm related to Ce3+ in the YAG host. The XRD results showed that high temperatures and inert atmosphere conditions were favorable to the growth of the YAG crystal. When the YAG:Ce samples were sintered in an inert atmosphere, the conversion of Ce3+ to Ce4+ could be suppressed effectively. Meanwhile, the CL intensity around 370 nm related to the antisite defects (AD) in the YAG lattice decreased significantly. Therefore, the YAG:Ce samples sintered in an inert atmosphere at high temperatures with a good crystal structure, high Ce3+ concentrations, and less AD had better luminescence properties. YAG:Ce samples synthesized using a co-precipitation method with excellent luminescence properties can be used as fast and efficient scintillation materials.

Scintillation Powders for the Detection of Neutrons

This paper presents scintillation powders, such as GdOBr:Ce, BaMgAl10O17:Eu, Mn, YAP:Ce, and YAG:Ce, for the detection of neutrons of wide energy ranges in connection with suitable conversion isotope. The influence of particle size of scintillators was studied as well as the fraction size of conversion powder. In addition, the proper mixture ratio was also investigated. Several powders are commercially available, but not used in neutron detectors. The inaccessible powders were self-prepared by solid-state synthesis. At the beginning, the response of selected scintillation powders to alpha and gamma radiation was studied. The results and properties of chosen scintillators were compared with ZnS:Ag in connection with 6LiF. This paper aims to take advantage of current knowledge in the field of scintillation materials synthesis and to find a fast scintillation material with properties similar to ZnS:Ag.

Scintillation and luminescence properties of a single CsCaCl3 crystal

We synthesized a fast scintillation material based on a ternary halide crystal, CsCaCl3, which is known to exhibit Auger-free luminescence (AFL) under core-level excitation. We characterized its luminescence properties using vacuum ultraviolet (VUV) light for excitation. We observed a broad AFL band centered at approximately 300nm for the core hole excitation, with a decay time of 2.3ns. In addition to AFL, we observed several luminescence bands for interband and sub-band-gap excitation. The scintillation light yield was estimated to be 410photons/MeV. We observed a fast scintillation component due to the AFL having a decay time constant of 2.3ns. This fast component accounts for 58% of the total scintillation. These results indicate that a fast scintillation material was successfully fabricated, employing AFL as the luminescence mechanism based on a ternary halide crystal.

Synchrotron Radiation Study of Interconfigurational 5d-4f Luminescence of Pr3+ in KLuP2O7

The double phosphate KLuP2O7 doped with Pr3+ ions was prepared by solid-state reaction. The material obtained was characterized by powder X-ray diffraction. The luminescence spectroscopy and the excited state dynamics of this material were studied upon excitation with VUV synchrotron radiation. The 5d-4 f emission of Pr3+ upon both direct and band gap excitation was detected and assigned. The decay kinetics of the Pr3+ 5d-4 f emission is characterized by a decay time of about 20 ns and is nearly temperature independent within the range 8 - 300 K. Both dynamics and energy transfer peculiarities revealed in the study suggested good potentials for application of KLuP2O7:Pr3+ as a fast scintillator material.

Luminescence properties of CsI crystals grown from the melt treated by metals-getters

The processes of purification of CsI melt from admixtures by metals-getters (Ti, Ta, and Zr) are studied through two ways: investigation of change in concentration of oxide-ion entering from the getter into the melt and investigation of luminescence properties of CsI single crystals grown from the treated melt. The treatment by Ti does not lead to the removal of oxide-ions; however the growth melt is polluted by Ti species (Ti2O3). This causes drastic changes in the luminescence properties of CsI crystals. Their radioluminescence spectra do not contain the band caused by fast 7 and 30ns components (maximum at 308nm) and there arises a band (maximum 418nm) corresponding to slow microsecond component. The enterance of Ta leads to removal of oxide ions, but the interaction products (Ta2O5 or CsTaO3) are partially dissolved in CsI melt that leads to appearance in the radioluminescence spectrum of the intense band (maximum 416nm) caused by the slow component together with less intense band (maximum at 305nm) due to the fast components. Only treatment by Zr allows to suppression of the slow component completely. The radioluminescence spectrum of CsI crystals grown from the Zr-treated melt includes only one band (maximum at 306nm), whereas the luminescence at wavelengths more than 410nm is absent. For this crystal two parameters describing its performance are determined. The effective time of luminosity of the fast components is equal to 14ns and the ‘Fast/Total’ ratio is 0.88. So, the treatment of CsI melt by Zr allows obtaining an extremely fast scintillation material.

Further performance tests of a picosecond X-ray and laser induced streak camera system with fast scintillation materials

A further performance test of a fluorescence lifetime spectroscopy system with 2D-photon counting based on a streak camera was carried out. This system offers three different excitation light sources. It includes a pulsable X-ray tube with 40 kV and a laser. A pulsed UV-LED has been installed for sample excitation. The table top measurement device has a temporal resolution down to 20 ps after deconvolution and fluorescence/scintillation decay times can be evaluated in a wavelength selectable range between 200 and 850 nm. Cesium fluoride, cesium chloride and cesium bromide as fast core-valence luminescence emitters with a relatively low light yield were used in the presented performance test. The easily manageable system is able to detect low light levels and to determine the decay times in agreement with literature in most instances. Beside mentioned scintillators PbCO3, SrI2 and Lu2SiO5:Ce as a high light yield material were also measured.

Study of Silicon Photomultipliers for the GRIPS Calorimeter Module

GRIPS is a proposed gamma-ray (200 keV to 80 MeV) astronomy mission, which incorporates a pair-creation and Compton scattering telescope, along with X-ray and infrared telescopes. It will carry out a sensitive all-sky scanning survey, investigating phenomena such as gamma-ray bursts, blazars and core collapse supernovae. The main telescope is composed of a Si strip detector surroundedby a calorimeter with a fast scintillator material. We present the initial results of a study which considers the potential use of silicon photomultipliers in conjunction with the scintillator in the GRIPS calorimeter module.