Single Crystal Scintillators Research Articles

X-ray radiation excited ultralong (>20,000 seconds) intrinsic phosphorescence in aluminum nitride single-crystal scintillators

Phosphorescence is a fascinating photoelectronic phenomenon usually observed in rare-earth-doped inorganic crystals and organic molecular crystals, owning great potential in optical information storage, color display and biological dosimetry. Here, we present an ultralong intrinsic phosphorescence (>20,000 seconds) in AlN single-crystal scintillator through X-ray excitation. We suggest that the long afterglow emission originates from the intra-band transition related to native nitrogen vacancy. Some excited states formed by absorbing X-ray photons cannot satisfy the parity difference between initial and final states required by transition selection rule, so they cannot return to the ground state directly through radiation transitions but through several phonon-assisted intra-band transitions slowly. During this process, a long-term broad-spectra phosphorescence emission is formed. Investigating the X-ray excited phosphorescence emission in the AlN is of great significance to understanding the mechanism of phosphorescence in inorganic materials, and to realizing the practical applications in high-energy ray dosimetry.

Optical and x–ray scintillation properties of X2MnCl4 (X = PEA, PPA) perovskite crystals

An emerging prospect of solution-processed organic–inorganic hybrid halide perovskites is promising for next generation x-ray imaging applications. Herein, the optical and x-ray scintillation properties of lead-free two-dimensional perovskite crystals are reported, i.e. X2MnCl4 (X = PEA, PPA). At room temperature (RT), the photoluminescence (PL) spectra of both crystals show a peak around 600 nm with the lifetime between 3 and 4 µs, making them applicable for scintillator in x-ray imaging applications. Materials with a small electronic band gap of about 2 eV may allow a good promise for high-light-yield scintillators. On the other hand, x-ray luminescence (XL) measurements for both crystals show no spectra at RT, while those at 10 K exhibit the similar features observed in PL spectra. Temperature-dependent XL intensities reveal thermal quenching behaviour with activation energies between 40 and 54 meV. Thermoluminescence (TL) and glow curves in both crystals show residual luminescence background as slow as 1648 s and some deep traps with energies as large as 190 meV. Thermal quenching and TL measurements of both crystals are the opposite of those of PEA2PbCl4 crystals. Although some properties may not be beneficial for scintillators, the small differences of scintillation properties in both crystals may provide direction for the new designs of high-light-yield lead-free perovskite single crystal scintillators.

Characterization of stilbene’s scintillation anisotropy for recoil protons between 0.56 and 10 MeV

The scintillation anisotropy of the single-crystal organic scintillator trans-stilbene was characterized for recoil protons between 0.56 and 10 MeV. The light output and pulse shape anisotropies were measured at 11 distinct recoil proton energies for over 168 recoil proton trajectories relative to the crystal axes. The measurements were performed using a neutron scatter kinematic measurement system and quasi-monoenergetic neutron beams produced by the tandem Van de Graaff accelerator at Triangle Universities Nuclear Laboratory (TUNL). The extensive recoil proton directional coverage enables interpolation over both energy and direction to form a complete response function of stilbene’s scintillation anisotropy for the measured energy range.

Recent advances, challenges, and opportunities of inorganic nanoscintillators.

This review article highlights the exploration of inorganic nanoscintillators for various scientific and technological applications in the fields of radiation detection, bioimaging, and medical theranostics. Various aspects of nanoscintillators pertaining to their fundamental principles, mechanism, structure, applications are briefly discussed. The mechanisms of inorganic nanoscintillators are explained based on the fundamental principles, instrumentation involved, and associated physical and chemical phenomena, etc. Subsequently, the promise of nanoscintillators over the existing single-crystal scintillators and other types of scintillators is presented, enabling their development for multifunctional applications. The processes governing the scintillation mechanisms in nanodomains, such as surface, structure, quantum, and dielectric confinement, are explained to reveal the underlying nanoscale scintillation phenomena. Additionally, suitable examples are provided to explain these processes based on the published data. Furthermore, we attempt to explain the different types of inorganic nanoscintillators in terms of the powder nanoparticles, thin films, nanoceramics, and glasses to ensure that the effect of nanoscience in different nanoscintillator domains can be appreciated. The limitations of nanoscintillators are also highlighted in this review article. The advantages of nanostructured scintillators, including their property-driven applications, are also explained. This review article presents the considerable application potential of nanostructured scintillators with respect to important aspects as well as their physical and application significance in a concise manner.

Tungsten co-doping effects on Ce:Gd3Ga3Al2O12 scintillator grown by the micro-pulling down method

Single crystal scintillators are extensively used in various radiation detection applications and their scintillation performances can be improved via co-doping. Therefore, in this study, tungsten-ion co-doped Ce:Gd3(Ga,Al)5O12 (Ce:GGAG) crystals were grown using the micro-pulling-down (μ-PD) method to investigate the effects of co-doping on their scintillation properties. The relationships between the W concentration, optical and luminescence properties, and radiation response of the W-co-doped Ce:GGAG crystals were evaluated. The W-co-doped Ce 0.5%:Gd3Ga3Al2O12 single crystals of diameter 3 mm and length 30–60 mm were grown by the μ-PD method. The light yield increased at W concentrations of 200 and 500 ppm and decreased at W concentrations above 1000 ppm. There was no significant change in the fast decay component of scintillation.

Resolution limits of a single crystal scintillator based X-ray micro-radiography camera

Recently, high resolution micro-radiography became of great interest. Very thin scintillator layers of about 5–20 micrometres are used to achieve spatial resolution below one micrometre in application for low energy X-ray micro-radiography [1]. Such thin screens are mainly used in micro-XCT and nano-XCT systems (X-ray Computed Tomography) with either micro-focus X-ray tubes or with synchrotron sources [2]. This work deals with a high-resolution CCD camera together with different optical systems and different single crystal scintillators in application for low energy X-ray micro-radiography. The light distribution on the screen is re-imaged by an optical system (usually represented by classical microscope objective together with a field lens) to a high-resolution CCD or CMOS chip. A theoretical modelling and practical comparison of a camera set-up has been done to investigate the system resolution limits. Thin screens were prepared from YAG:Ce scintillator. The resolution is presented on test patterns. As recent optical systems are limited to the classical microscopy objectives only, we further investigate a possibility to develop a custom-made objective fully dedicated to X-ray imaging application.

High-sensitivity X-ray imaging of a lead halide perovskite single-crystal scintillator

Low-dose rate detection and high contrast are required to reduce unwanted ionization irradiation for X-ray imaging procedure. Recently, low-cost solution-processed hybrid lead halide perovskite has been demonstrated for direct X-ray detection. However, the performances are limited by the relative poor charge collection. Here we report an organic-inorganic perovskite single-crystal scintillator with high sensitivity for X-ray imaging. High-quality scintillator crystals have been synthesized using the solution-processed method at a low temperature with X-ray excited light emission wavelength of 432 nm. The lowest detectable dose rate is 114.7 n G y s − 1 , which is comparable with the best perovskite-based photoconductor X-ray detector for a 50 keV X-ray. We achieved a high-contrast X-ray image that proves the feasibility for medical applications.

Modified vertical Bridgman method: Time and cost effective tool for preparation of Cs2HfCl6 single crystals

Abstract Time and cost effective methods are highly desirable in research and development of new scintillators. Modern techniques like micro-pulling down (μ-PD) are suitable for material screening but are unfit for the growth of some crystals. These crystals must be grown by different methods that are usually very time demanding. Modification of halide μ-PD apparatus by custom made elements allowed us to grow cesium hafnium chloride (Cs2HfCl6) by vertical Bridgman method (VB) with significantly reduced growth time. Structural and optical properties of samples prepared from as-grown crystals were studied and compared to crystals grown by standard VB method. The X-ray diffraction confirmed the formation of cesium hafnium chloride single-phase and natural cleavage of the crystals along the (1 1 1) crystallographic plane. Photoluminescence emission, excitation, absorption, and radioluminescence spectroscopy revealed that the optical quality of the crystals grown by modified VB method was comparable to the quality of the crystals grown by standard VB method. Therefore we can use samples prepared by modified VB to estimate and optimize the performance of Cs2HfCl6 based crystals in scintillation detectors. This setup allows the time and cost-effective material screening and it is a powerful tool for the development of new halide based single crystal scintillators.

Engineering of a new single-crystal multi-ionic fast and high-light-yield scintillation material (Gd0.5–Y0.5)3Al2Ga3O12:Ce,Mg

A single crystal scintillation material (Gd0.5–Y0.5)3Al2Ga3O12 (GYAGG) doped with Ce and codoped with Mg at a small concentration was grown by the Czochralski technique and studied for its scintillation properties for the first time.

Luminescence efficiency of CaF2:Eu single crystals: Temperature dependence

During the last decades, there is increasing interest in applications of scintillators at harsh environments (i.e., high temperatures or radiation fluxes), such as in geophysical detectors for deep geology boreholes, non-destructive testing (NDT) of pipelines in oil and gas industry, space and marine exploration, nuclear reactor monitoring, radiation chemistry, etc. To this aim, the current study is the first step towards the investigation of the luminescence efficiency dependence of single-crystal scintillators over wide temperature ranges. Calcium fluoride doped with europium (CaF2:Eu) was selected due to the fact that it has a high melting point at 1418°C and is also robust to mechanical and thermal shocks. The dimensions of the single-crystal sample were 10x10x10 mm3, and it was irradiated using typical X-ray radiographic exposures (90 kVp, 63mAs) in order to measure the light photon intensity dependence with temperature (22 to 128 °C). The luminescence efficiency was found maximum at the lowest examined temperature (22.01 efficiency units-E.U. at 22 °C-environmental). With increasing temperature, the luminescence efficiency decreased almost exponentially due to thermal quenching (4.43 efficiency units-E.U. at 128 °C).

Temperature Dependence of the Luminescence output of CdWO4 Crystal. Comparison with CaF2:Eu

Scintillators are radiation converters applied in medical imaging detectors, in applications at harsh environments, including in geophysical detectors for deep geology boreholes, non-destructive testing (NDT) in gas and oil facilities, space, marine exploration, etc. In this study the luminescence efficiency dependence of single-crystal scintillators was examined with increasing temperature. Cadmium tungstate (CdWO4) was examined against calcium fluoride doped with europium (CaF2:Eu). The dimensions of the single crystals’ samples were 10x10x10 mm3 and were irradiated using X-ray radiographic exposures (90 kVp, 63mAs) to measure the light output with temperature (22 to 128 °C). The luminescence efficiency was found in both cases maximum at the lowest examined temperature (23.06 efficiency units-E.U for CdWO4 and 22.01 E.U. for CaF2:Eu, at 22 °C-environmental). With increasing temperature, the luminescence efficiency constantly decreased for both crystals due to thermal quenching (5.32 efficiency units for CdWO4 and 4.43 for CaF2:Eu, at 128 °C). In the mid-range (50-80 °C) CdWO4 shows increased differences compared to CaF2:Eu. CdWO4 has a higher density (7.9 g/cm 3) and luminescence signal than CaF2:Eu (3.18 g/cm 3), thus it is suitable, besides medical imaging, also for operation in harsh environments.

Czochralski growth, electronic structure, luminescence and scintillation properties of Cs2Mo3O10: A new scintillation crystal for 0νββ decay search

A new molybdenum (Mo) based Cesium tri-molybdate (Cs2Mo3O10) single crystal scintillator has been grown successfully by the Czochralski technique. The crystal growth conditions such as pulling, rotation and cooling rate were optimized for crack free high-quality single crystals. The electronic band structure has been calculated with density functional theory using projector augmented wave potentials as implemented in the Vienna ab initio Simulation Package. The major contribution in the formation of valence band near the fermi level is observed from Mo and O p orbitals while the bottom of the conduction band mainly consists from Mo-d and O-p states. The grown crystal possesses good transparency above the fundamental absorption edge in the wavelength range of 400–900 nm. Optical band gap of 3 eV is estimated from the absorption spectra measured at room temperature. Luminescence and scintillation properties were measured in the temperature range of 10–300 K under the excitation of UV light at 4.42 eV, X-rays and beta rays. The emission spectrum measured at 230 K is comprising of a single band peaking at 645 nm, which intensity is enhanced with the cooling of crystal. A single exponential photoluminescent decay time of 43 μs is obtained at 220 K which further slows down upon cooling of the crystal and found to be 1.64 ms at 10 K. The scintillation light yield of Cs2Mo3O10 crystal at 10 K is found to be 185% of Li2MoO4 (LMO) crystal. The thermally stimulated luminescence (TSL) kinetic parameters such as trap depth and frequency factor from the glow curve measured after X-ray irradiation at 10 K, have been determined using general order kinetics. A possibility of crystal growth with large volume, good optical, luminescence and scintillation properties reveal that this scintillation material can be a good candidate for the neutrinoless double beta (0νββ) decay search of 100Mo.

Characterizations of Pr:Ca2Al2SiO7 single crystal scintillator for α-ray detection

Undoped and Pr-doped Ca2Al2SiO7 single crystals were synthesized by the floating zone method. The X-ray diffraction patterns confirmed that all the crystals have no impurity phases. Pr-doped crystals show photoluminescence with broad emission bands from 250 to 400 nm and sharp emission lines from 500 to 800 nm due to the 5d-4f and 4f-4f transitions of Pr3+, respectively. Under VUV photon excitation using a synchrotron source, the undoped crystal shows broad emission bands around 380 and 600 nm considered to be due to self-trapped excitons (STEs). The PL decay time constants of the Pr-doped crystals are 15–19 ns and 23–56 μs. The scintillation spectra of Pr-doped crystals are different compared with PL spectra, and the emissions consist of emission peaks due to Pr3+ as well as the STEs. From the pulse height spectra measured using the Pr-doped crystals under 241Am 5.5 MeV α-rays, all the crystals exhibit a clear peak of full-energy absorption, and the 3.0% Pr-doped crystal shows the highest scintillation light yield of 2,600 ph/5.5 MeV-α.

Observations regarding inclusions in the growth of Cs2HfCl6 single crystal scintillators

Cs2HfCl6 (CHC) is a promising high density, high-Z, non-hygroscopic, and high energy resolution scintillator. In CHC, many crystals have CsCl inclusions that form during growth. In this paper, we investigate how material synthesis, growth rate, and thermal gradient affect the formation of CsCl inclusions and their effect on scintillation performance. First, precursor material was made through a methanol synthesis process both with and without hydrochlorination. Next, five crystals were grown using Bridgman method, at growth rates of 1 or 0.5 mm/h, and thermal gradients of 21 °C or 34 °C per millimeter. The best overall performance was observed in a 22 mm diameter crystal produced using hydrochlorination which was grown at 1 mm/h in a thermal gradient of 34 °C per millimeter. It had a light yield of 36,000 photons/MeV and an energy resolution of 4.0% at 662 keV. We have also shown that poorer scintillation performance in the lower quality crystals is most likely due to reduced light collection caused by a higher concentration of inclusions.

A novel versatile phoswich detector consisting of single crystal scintillators

The discrimination of different types of radiations like gamma, charged particles, neutrons etc., is required in various applications in Academic, the Nuclear industry, homeland security, medical diagnostics, etc. For these versatile uses, we have developed a novel phoswich detector consisting of two promising single crystal scintillators to discriminate various kinds of radiation with a promising figure-of-merit (FOM) along with advantages over other single crystal scintillators reported so far. The high pulse-shape discrimination (PSD) for different radiations has been achieved by a novel combination of a Boron co-doped Gd3Ga3Al2O12:Ce (GGAG) crystal coupled to a CsI:Tl (CsI) single crystal in a phoswich detector design. This combination was optically coupled to a single photomultiplier tube and a desktop digitizer to build a compact detector setup. The FOM for discriminating alpha and gamma radiations was observed to be better than twice that of the FOM obtained using individual crystals. The gamma interacting in the front GGAG crystal and the back CsI crystal could also be discriminated with a distinguishing FOM that may lead to notable improvement of spatial resolution in the medical imaging applications. The gamma–gamma discrimination and the presence of Gd in GGAG makes it a suitable candidate for the detection of thermal neutrons in mixed fields. Overall, the observed significant improvement in the discrimination ability along with the remarkable versatility opens a vast scope for using this combination in various applications.

Neutron/γ discrimination by an emission-based phoswich approach

Particle discrimination in a mixed radiation field using scintillators is a challenging topic in radiation detection research. We propose a novel approach relying on the possibility of identifying particles interacting in a phoswich detector from the emission spectrum of the produced scintillation signal. As a proof of concept, we focus on the discrimination between neutrons and gamma rays.Lu3Al5O12:Pr and Gd3Al2Ga3O12:Ce thin single crystal scintillators, coupled to two different silicon photomultipliers equipped with optical filters, are simultaneously used in the same phoswich detector. Their optical emissions peak at approximately 310 nm and 545 nm respectively, and thus they can easily be distinguished by optical filtering. While both crystals are sensitive to gamma rays, neutrons interact only with the Gd3Al2Ga3O12:Ce thanks to the presence of Gd acting as neutron converter. Optical filtration and an anti-coincidence algorithm are therefore used to perform particle discrimination, rejecting coincidence signals arising from gamma rays, which simultaneously deposit energy in both crystals, and counting anti-coincidence signals due to neutrons, which deposit energy only in the Gd3Al2Ga3O12:Ce.The simple neutron counter developed here is intended to be a proof of the principle of the feasibility of the color-based particle discrimination technique.

Effect of lithium codopant concentration on the luminescence properties of (Lu0.75Y0.25)3Al5O12: Pr3+ single crystals: Before and after air annealing

In this paper, we present the photoluminescence and scintillation performance of Pr3+ doped (Lu0.75Y0.25)3Al5O12 single crystals as a function of Li+ concentration. Lithium concentration had no effect on the optical properties of LuYAG: Pr single crystal scintillators regardless of concentration. On the other hand, scintillation light yield increased by as much as 94% with the incorporation of lithium as a codopant, and the energy resolution at 662 keV was improved to 4.1%, which is an outstanding energy resolution for an oxide single crystal scintillator. Lithium codoping slightly lengthened the fast component of the scintillation decay time, and slightly decreased the contribution from the slow component. Additionally, the samples were annealed in air and scintillation properties were compared before and after this annealing treatment. The change in scintillation properties is explained through the analysis of thermoluminescence glow curves.

Development of instruments for space exploration using meteorological balloons

Indian Centre for Space Physics is engaged in studying terrestrial and extra-terrestrial high energy phenomena from meteorological balloon borne platforms. A complete payload system with such balloons is at the most about five kilograms of weight. One has to adopt innovative and optimal design for various components of the experiment, so that the data can be procured at decent heights of ~ 35-42 km and at the same time, some scientific goals are achieved. In this paper, we mainly describe the instruments in detail and present their test and calibration results. We discuss, how we implemented and tested three major instruments, namely, a Geiger-M\"uller counter, a single crystal scintillator detector and a phoswich type scintillator detector for our missions. We also present some flight data of a few missions to demonstrate the capability of such experiments.

Scintillation response of Europium and Indium-co-doped CsI(Na) single crystal under the exposure of gamma-ray

The traditional CsI(Na) single crystal scintillator was studied to improve its scintillation properties, by co-doping Sodium with Europium and Indium ions. The growth was done by the Czochralski technique. Inductively coupled plasma optical emission spectroscopy and UV spectra including the absorption, excitation, and photoluminescence of the cut ingots were obtained in the region of 200 to 800 nm. The results show that the luminescence intensity of Europium-co-doped CsI(Na) is significantly increased compared to CsI(Na) single crystal, however Indium co-dopant has reduced the CsI(Na) luminescence intensity. Eu’s high quantum emission efficiency due to its 4f → 5d internal transitions and the radiative energy transfer between Na + and Eu 2 + centers are the possible reason for this enhancement. While decreasing the CsI(Na) luminescence intensity, by adding the In co-dopant, is probably due to non-constructive spectral overlap between emission transition of In + and absorption transition of Na + which results in non-radiative energy transfer between Na + and In + . In this regard, the pulse height spectrum of these crystals was determined under the excitation of the gamma-ray sources. It is observed that Eu co-dopant strongly increases the scintillation light yield of the conventional CsI(Na) detector and improves its energy resolution, however In co-doped CsI(Na) reduces scintillation yield.

Optimization of Parameters for a CsI(Tl) Scintillator Detector Using GEANT4-Based Monte Carlo Simulation Including Optical Photon Transport

GEANT4-based Monte Carlo simulation has been performed for a 2"φ × 2" L cylindrical CsI(Tl) single-crystal scintillator. The simulation includes transport of incident gamma photons as well as generation and transport of optical photons in the crystal up to the coupled photodetector. An optical photon detection spectrum was generated from the number of optical photons detected at the photodetector surface per incident primary gamma photon. This spectrum is equivalent to a conventional pulse-height spectrum, apart from the fact that its abscissa is only proportional, but not equal, to the actual pulse height (volts). This has an energy resolution of about 6.5% at 662 keV arising from the light generation and transport statistics. This spectrum was compared with an experimentally recorded pulse-height spectrum (after the abscissa of both the spectra were converted to energy scale) from a gamma spectrometer based on an in-house grown 2"φ × 2" L cylindrical CsI(Tl) crystal, thereby validating the simulation code. The effects of variation of scintillation and optical properties as well as physical and surface parameters on the simulated spectrum were subsequently studied in order to identify the important parameters. The quantum efficiency of the photodetector and the matching of its spectral response with the emission spectrum of the scintillator, reflectivity of the scintillator coating material, and the absolute light yield of the scintillator were identified as the parameters that influence the pulse-height spectrum in the most dominant way. Results of simulation presented in this paper are likely to facilitate the optimization of future detector setups.