Bright Innovations: Review of Next-Generation Advances in Scintillator Engineering

This review focuses on modern scintillators, the heart of ionizing radiation detection with applications in medical diagnostics, homeland security, research, and other areas. The conventional method to improve their characteristics, such as light output and timing properties, consists of improving in material composition and doping, etc., which are intrinsic to the material. On the contrary, we review recent advancements in cutting-edge approaches to shape scintillator characteristics via photonic and metamaterial engineering, which are extrinsic and introduce controlled inhomogeneity in the scintillator's surface or volume. The methods to be discussed include improved light out-coupling using photonic crystal (PhC) coating, dielectric architecture modification producing the Purcell effect, and meta-materials engineering based on energy sharing. These approaches help to break traditional bulk scintillators' limitations, e.g., to deal with poor light extraction efficiency from the material due to a typically large refractive index mismatch or improve timing performance compared to bulk materials. In the Outlook section, modern physical phenomena are discussed and suggested as the basis for the next generations of scintillation-based detectors and technology, followed by a brief discussion on cost-effective fabrication techniques that could be scalable.

High-Resolution X-ray Image from Copper-Based Perovskite Hybrid Polymer

Cs3Cu2I5 nanocrystals (NCs) are considered to be promising materials due to their high photoluminescence efficiency, lack of lead toxicity, and X-ray responsiveness. However, during the crystallization process, NCs are prone to agglomeration and exhibit uneven size distribution, resulting in several light scattering that severely affect their imaging resolution. Herein, we successfully developed a high-resolution scintillator film by growing copper-based perovskite NCs within a hybrid polymer matrix. By leveraging the ingenious integration of polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA), the size and distribution uniformity of Cs3Cu2I5 NCs can be effectively controlled. Consequently, a high spatial resolution of 14.3 lp mm-1 and a low detection limit of 105 nGy s-1 are achieved, and the scintillator film has excellent flexibility and stability. These results highlight the promising application of Cs3Cu2I5 scintillator films in low-cost, flexible, and high-performance medical imaging.

Metal Halide Nanocrystals@Silica Aerogel Composite with Enhanced Dispersion Stability and Light Output for Efficient X-Ray Imaging in Harsh Environment

Metal halide nanocrystals (MHNCs) embedded in a polymer matrix as flexible X-ray detector screens is an effective strategy with the advantages of low cost, facile preparation, and large area flexibility. However, MHNCs easily aggregate during preparation, recombination, under mechanical force, storage, or high operating temperature. Meanwhile, it shows an unmatched refractive index with polymer, resulting in low light yield. The related stability and properties of the device remain a huge unrevealed challenge. Herein, a composite screen (CZBM@AG-PS) by integrating MHNCs (Cs2ZnBr4: Mn2+ as an example) into silica aerogel (AG) and embedded in polystyrene (PS) is successfully developed. Further characterization points to the high porosity AG template that can effectively improve the dispersion of MHNCs in polymer detector screens, essentially decreasing nonradiative transition, Rayleigh scattering, and performance aging induced by aggregation in harsh environments. Furthermore, the higher light output and lower optical crosstalk are also achieved by a novel light propagation path based on the MHNCs/AG and AG/PS interfaces. Finally, the optimized CZBM@AG-PS screen shows much enhanced light yield, spatial resolution, and temperature stability. Significantly, the strategy is proven universal by the performance tests of other MHNCs embedded composite films for ultra-stable and efficient X-ray imaging.

Organosilicon-Based Ligand Design for High-Performance Perovskite Nanocrystal Films for Color Conversion and X-ray Imaging

Perovskite nanocrystals (PNCs) bear a huge potential for widespread applications, such as color conversion, X-ray scintillators, and active laser media. However, the poor intrinsic stability and high susceptibility to environmental stimuli including moisture and oxygen have become bottlenecks of PNC materials for commercialization. Appropriate barrier material design can efficiently improve the stability of the PNCs. Particularly, the strategy for packaging PNCs in organosilicon matrixes can integrate the advantages of inorganic-oxide-based and polymer-based encapsulation routes. However, the inert long-carbon-chain ligands (e.g., oleic acid, oleylamine) used in the current ligand systems for silicon-based encapsulation are detrimental to the cross-linking of the organosilicon matrix, resulting in performance deficiencies in the nanocrystal films, such as low transparency and large surface roughness. Herein, we propose a dual-organosilicon ligand system consisting of (3-aminopropyl)triethoxysilane (APTES) and (3-aminopropyl)triethoxysilane with pentanedioic anhydride (APTES-PA), to replace the inert long-carbon-chain ligands for improving the performance of organosilicon-coated PNC films. As a result, strongly fluorescent PNC films prepared by a facile solution-casting method demonstrate high transparency and reduced surface roughness while maintaining high stability in various harsh environments. The optimized PNC films were eventually applied in an X-ray imaging system as scintillators, showing a high spatial resolution above 20 lp/mm. By designing this promising dual organosilicon ligand system for PNC films, our work highlights the crucial influence of the molecular structure of the capping ligands on the optical performance of the PNC film.

A comprehensive investigation of the performance of a commercial scintillator system for applications in electron FLASH radiotherapy

BACKGROUND

Dosimetry in ultra-high dose rate (UHDR) beamlines is significantly challenged by limitations in real-time monitoring and accurate measurement of beam output, beam parameters, and delivered doses using conventional radiation detectors, which exhibit dependencies in ultra-high dose-rate (UHDR) and high dose-per-pulse (DPP) beamline conditions.

PURPOSE

In this study, we characterized the response of the Exradin W2 plastic scintillator (Standard Imaging, Inc.), a water-equivalent detector that provides measurements with a time resolution of 100 Hz, to determine its feasibility for use in UHDR electron beamlines.

METHODS

The W2 scintillator was exposed to an UHDR electron beam with different beam parameters by varying the pulse repetition frequency (PRF), pulse width (PW), and pulse amplitude settings of an electron UHDR linear accelerator system. The response of the W2 scintillator was evaluated as a function of the total integrated dose delivered, DPP, and mean and instantaneous dose rate. To account for detector radiation damage, the signal sensitivity (pC/Gy) of the W2 scintillator was measured and tracked as a function of dose history.

RESULTS

The W2 scintillator demonstrated mean dose rate independence and linearity as a function of integrated dose and DPP for DPP ≤ 1.5 Gy (R2 > 0.99) and PRF ≤ 90 Hz. At DPP > 1.5 Gy, nonlinear behavior and signal saturation in the blue and green signals as a function of DPP, PRF, and integrated dose became apparent. In the absence of Cerenkov correction, the W2 scintillator exhibited PW dependence, even at DPP values <1.5 Gy, with a difference of up to 31% and 54% in the measured blue and green signal for PWs ranging from 0.5 to 3.6 µs. The change in signal sensitivity of the W2 scintillator as a function of accumulated dose was approximately 4%/kGy and 0.3%/kGy for the measured blue and green signal responses, respectively, as a function of integrated dose history.

CONCLUSION

The Exradin W2 scintillator can provide output measurements that are both dose rate independent and linear in response if the DPP is kept ≤1.5 Gy (corresponding to a mean dose rate up to 290 Gy/s in the used system), as long as proper calibration is performed to account for PW and changes in signal sensitivity as a function of accumulated dose. For DPP > 1.5 Gy, the W2 scintillator's response becomes nonlinear, likely due to limitations in the electrometer related to the high signal intensity.

Magnetic field influence on the light yield from fiber-coupled BCF-60 plastic scintillators of relevance for output factor dosimetry in MR-linacs

Organic plastic scintillators are of interest for ionizing radiation dosimetry in megavoltage photon beams because plastic scintillators have a mass density very similar to that of water. This leads to insignificant perturbation of the electron fluence at the point of measurement in a water phantom. This feature is a benefit for dosimetry in strong magnetic fields (e.g., 1.5 T) as found in linacs with magnetic resonance imaging. The objective of this work was to quantify if the light yield per dose for the scintillating fiber BCF-60 material from Saint-Gobain Ceramics and Plastics Inc. is constant regardless of the magnetic flux density. This question is of importance for establishing traceable measurement in MR linacs using this detector type. Experiments were carried out using an accelerator combined with an electromagnet (max 0.7 T). Scintillator probes were read out using chromatic stem-removal techniques based on two optical channels or full spectral information. Reference dosimetry was carried out with PTW31010 and PTW31021 ionization chambers. TOPAS/GEANT4 was used for modelling. The light yield per dose for the BCF-60 was found to be strongly influenced by the magnitude of the magnetic field from about 1 mT to 0.7 T. The light yield per dose increased (1.3 ± 0.2)% (k = 1) from 1 mT to 10 mT and it increased (4.5 ± 0.9)% (k = 1) from 0 T to 0.7 T. Previous studies of the influence of magnetic fields on medical scintillator dosimetry have been unable to clearly identify if observed changes in scintillator response with magnetic field strength were related to changes in dose, stem signal removal, or scintillator light yield. In the current study of BCF-60, we see a clear change in light yield with magnetic field, and none of the other effects.

Bright Transparent Scintillators with High Fraction BaCl2 : Eu2+ Nanocrystals Precipitation: An Ionic-Covalent Hybrid Network Strategy toward Superior X-Ray Imaging Glass-Ceramics

Metal halide crystals are bright but hygroscopic scintillator materials that are widely used in X-ray imaging and detectors. Precipitating them in situ in glass to form glass ceramics (GCs) scintillator offers an efficient avenue for large-scale preparation, high spatial resolution, and excellent stability. However, precipitating a high fraction of metal halide nanocrystals in glass to maintain high light yield remains a challenge. Herein, an ionic-covalent hybrid network strategy for constructing GCs scintillator with high crystallinity (up to ≈37%) of BaCl2 : Eu2+ nanocrystals is presented. Experimental data and simulations of glass structure reveal that the Ba2+ -Cl- clustering promotes the high crystallization of BaCl2 nanocrystals. The ultralow phonon energy (≈200 cm-1 ) of BaCl2 nanocrystals and good Eu reduction effect enable high photoluminescence inter quantum efficiency (≈80.41%) in GC. GCs with varied crystallinity of BaCl2 : Eu2+ nanocrystals demonstrate efficient radioluminescence and tunable scintillator performance. They either outperform Bi4 Ge3 O14 single crystal by over 132% steady-state light yield or provide impressive X-ray imaging resolutions of 20 lp mm-1 . These findings provide a new design strategy for developing bright transparent GCs scintillators with a high fraction of metal halide nanocrystals for X-ray high-resolution imaging applications.

Photoluminescence of Cesium-Doped Sodium Iodide Films Irradiated by UV LED

Alkali metal halides have long been used as scintillators for applications as sensors and detectors. Usually, a small amount of impurities are added to these inorganic materials to improve their luminescence efficiencies. We investigate the structures and luminescent properties of un-doped sodium iodide (NaI) and cesium-doped NaI (NaI:Cs) films deposited by thermal vacuum evaporation. Instead of using the toxic element thallium (Tl), we introduced cesium dopant into NaI. This is the first study for the NaI:Cs film excited by UV LED's ultraviolet C (273 nm, 4.54 eV). The luminescence spectra show two main peaks at 3.05 and 4.32/3.955 eV (for fused silica/B270 substrate), originating from the intrinsic defects and/or activator excited states and the intrinsic self-trapped excitons (STEs), respectively. In general, both Cs-doping and post-annealing processes enhance the luminescence performance of NaI films.

High-Quality Cs3Cu2I5@PMMA Scintillator Films Assisted by Multiprocessing for X-ray Imaging

In recent years, novel metal halide scintillators have shown great application potential due to their tunable emission wavelength, high X-ray absorption, and high luminescence efficiency. However, poor stability and complex device packaging remain key issues for metal halide scintillators, making it difficult to achieve high-resolution and flexible X-ray imaging applications. To address the above issues, a multiprocessing strategy was introduced to prepare Cs3Cu2I5@PMMA scintillator films for long-term stable application, mainly undergo different annealing treatments to make Cs3Cu2I5 crystals to accurately nucleate and then grow in-situ in the PMMA matrix. Then, a series of characterization results illustrate that the prepared Cs3Cu2I5@PMMA scintillator films have high crystallinity, uniform size, excellent flexibility, high stable photoluminescence (PL) and radioluminescence (RL) performance, and high-resolution X-ray imaging capability. Most importantly, Cs3Cu2I5@PMMA scintillator films can not only provide clear and accurate imaging recognition of objects with different complex structures but also maintain stable X-ray imaging quality within 60 days and can achieve flexible X-ray imaging. Therefore, we have provided an effective strategy for producing high-quality scintillator films to meet the multidimensional needs of a new generation of scintillators.

The Influence of Halide Ion Substitution on Energy Structure and Luminescence Efficiency in CeBr2I and CeBrI2 Crystals

This study aims to determine the optimum composition of the CeBr_1-xI_x compound to achieve the maximum light output. It is based on calculations of the band energy structure of crystals, specifically taking into account the characteristics of the mutual location of local and band 5d states of the Ce³⁺ ions. The band energy structures for CeBr₂I and CeBrI₂ crystals were calculated using the projector augmented wave method. The valence band was found to be formed by the hybridized states of 4p Br and 5p I. The 4f states of Ce³⁺ are located in the energy forbidden band gap. The conduction band is formed by the localized 5d1 states, which are created by the interaction between the 5d states of Ce³⁺ and the 4f⁰ hole of the cerium ion. The higher-lying delocalized 5d2 states of Ce³⁺ correspond to the energy levels of the 5d states of Ce³⁺ in the field of the halide Cl⁰ (Br⁰) hole. The relative location of 5d1 and 5d2 bands determines the intensity of 5d-4f luminescence. The bottom of the conduction band is formed by localized 5d1 states in the CeBr₂I crystal. The local character of the bottom of the conduction band in the CeBr₂I crystal favors the formation of self-trapped Frenkel excitons. Transitions between the 5d1 and 4f states are responsible for 5d-4f exciton luminescence. In the CeBrI₂ crystal, the conduction band is formed by mixing the localized 5d1 and delocalized 5d2 states, which leads to quenching the 5d-4f luminescence and a decrease in the light output despite the decrease in the forbidden band gap. CsBr₂I is the optimum composition of the system to achieve the maximum light output.

Scintillation Properties of Ba3RE(PO4)3 Single Crystals (RE = Y, La, Lu)

Eulytite-type Ba₃RE(PO₄)₃ (RE = Y, La, and Lu) single crystals were synthesized by the floating zone method, and their scintillation properties were investigated. The powder X-ray diffraction measurement revealed that the single phase of Ba₃RE(PO₄)₃ samples were successfully synthesized. The samples exhibited a luminescence peak due to self-trapped exciton at around 400 nm under vacuum ultraviolet and X-ray irradiation. The X-ray-induced scintillation decay time constants of the samples were several microseconds at room temperature. In the ²⁴¹Am α-ray irradiated pulse height spectra, all the samples showed a clear full energy peak, and the absolute light yields of the Ba₃Y(PO₄)₃, Ba₃La(PO₄)₃, and Ba₃Lu(PO₄)₃ single crystals were estimated to be 960, 1160, and 1220 ph/5.5 MeV-α, with a typical error of ±10%, respectively. The scintillation light yields of the Ba₃RE(PO₄)₃ have been quantitatively clarified for the first time.

Design, testing and characterization of a proton central axis alignment device for the Dynamic Collimation System

OBJECTIVE

Proton therapy conformity has improved over the years by evolving from passive scattering to spot scanning delivery technologies with smaller proton beam spot sizes. Ancillary collimation devices, such the Dynamic Collimation System (DCS), further improves high dose conformity by sharpening the lateral penumbra. However, as spot sizes are reduced, collimator positional errors play a significant impact on the dose distributions and hence accurate collimator to radiation field alignment is critical. &#xD;Approach. The purpose of this work was to develop a system to align and verify coincidence between the center of the DCS and the proton beam central axis. The Central Axis Alignment Device (CAAD) is composed of a camera and scintillating screen-based beam characterization system. Within a light-tight box, a 12.3-megapixel camera monitors a P43/Gadox scintillating screen via a 45⁰ first-surface mirror. When a collimator trimmer of the DCS is placed in the uncalibrated center of the field, the proton radiation beam continuously scans a 7x7 cm² square field across the scintillator and collimator trimmer while a 7 second exposure is acquired. From the relative positioning of the trimmer to the radiation field, the true center of the radiation field can be calculated.&#xD;Main results. The CAAD can calculate the offset between the proton beam radiation central axis and the DCS central axis within 0.054 mm accuracy and 0.075 mm reproducibility.&#xD;Significance. Using the CAAD, the DCS is now able to be aligned accurately to the proton radiation beam central axis and no longer relies on an x-ray source in the gantry head which is only validated to within 1.0 mm of the proton beam.&#xD.

High Thermal Stability of Copper-Based Perovskite Scintillators for High-Temperature X-ray Detection

High-temperature scintillation detectors play a significant role in oil exploration. However, traditional scintillators have limited ability to meet the requirements of practical applications owing to their low thermal stability. In this study, we designed and developed a one-dimensional (1D) Cs₅Cu₃Cl₆I₂ scintillator with high thermal stability. In addition, by preparing Cs₅Cu₃Cl₇I, we proved that the Cs₅Cu₃Cl₆I₂ scintillator exhibits high thermal stability because the bridges linking the structural units in the 1D chain structure are only formed by I^- ions, which improve their structural rigidity. The scintillator has a high steady-state light yield (59,700 photons MeV^-1) and exhibits the highest spatial resolution for powder-based scintillation screens (18 lp mm^-1) after cyclic treatment within the temperature range of 298-423 K. The Cs₅Cu₃Cl₆I₂ scintillator allows the visualization of alloy melting, indicating that it has significant potential for application in high-temperature environments. This study provides a new perspective toward the design of scintillators with high thermal stability.

Large Scale BN-perovskite Nanocomposite Aerogel Scintillator for Thermal Neutron Detection

State-of-the-art thermal neutron scintillation detectors rely on rare isotopes for neutron capture, lack stability and scalability of solid-state scintillation devices, and poorly discriminate between the neutron and gamma rays. The boron nitride (BN)-CsPbBr₃ perovskite nanocomposite aerogel scintillator enables discriminative detection of thermal neutrons, features the largest known size (9 cm across), the lowest density (0.17 g cm^-3 ) among the existing scintillation materials, high BN (50%) perovskite (1%) contents, high optical transparency (85%), and excellent radiation stability. The new detection mechanism relies on thermal neutron capture by ¹⁰ B and effective energy transfer from the charged particles to visible-range scintillation photons between the densely packed BN and CsPbBr₃ nanocrystals. Low density minimizes the gamma ray response. The neutrons and gamma rays are discriminated by complete decoupling of the respective single pulses in time and intensity. These outcomes open new avenues for neutron detection in resource exploration, clean energy, environmental, aerospace, and homeland security applications.

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 Ca²⁺and Mg²⁺, 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 mm³LYSO: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 mm³pixels. 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.

High Quantum Efficiency Rare-Earth-Doped Gd2O2S:Tb, F Scintillators for Cold Neutron Imaging

High-resolution neutron radiography provides novel and stirring opportunities to investigate the structures of light elements encased by heavy elements. For this study, a series of Gd₂O₂S:Tb, F particles were prepared using a high-temperature solid phase method and then used as a scintillation screen. Upon reaching 293 nm excitation, a bright green emission originated from the Tb³⁺ luminescence center. The level of F doping affected the fluorescence intensity. When the F doping level was 8 mol%, the fluorescence intensity was at its highest. The absolute quantum yield of the synthesized particles reached as high as 77.21%. Gd₂O₂S:Tb, F particles were applied to the scintillation screen, showing a resolution on the neutron radiograph as high as 12 μm. These results suggest that the highly efficient Gd₂O₂S:Tb, F particles are promising scintillators for the purposes of cold neutron radiography.

X-ray Activated Nanoplatforms for Deep Tissue Photodynamic Therapy

Photodynamic therapy (PDT), the use of light to excite photosensitive molecules whose electronic relaxation drives the production of highly cytotoxic reactive oxygen species (ROS), has proven an effective means of oncotherapy. However, its application has been severely constrained to superficial tissues and those readily accessed either endoscopically or laparoscopically, due to the intrinsic scattering and absorption of photons by intervening tissues. Recent advances in the design of nanoparticle-based X-ray scintillators and photosensitizers have enabled hybridization of these moieties into single nanocomposite particles. These nanoplatforms, when irradiated with diagnostic doses and energies of X-rays, produce large quantities of ROS and permit, for the first time, non-invasive deep tissue PDT of tumors with few of the therapeutic limitations or side effects of conventional PDT. In this review we examine the underlying principles and evolution of PDT: from its initial and still dominant use of light-activated, small molecule photosensitizers that passively accumulate in tumors, to its latest development of X-ray-activated, scintillator-photosensitizer hybrid nanoplatforms that actively target cancer biomarkers. Challenges and potential remedies for the clinical translation of these hybrid nanoplatforms and X-ray PDT are also presented.

Color-Tunable and Stable Copper Iodide Cluster Scintillators for Efficient X-Ray Imaging

The search for color-tunable, efficient, and robust scintillators plays a vital role in the development of modern X-ray radiography. The radioluminescence tuning of copper iodide cluster scintillators in the entire visible region by bandgap engineering is herein reported. The bandgap engineering benefits from the fact that the conduction band minimum and valence band maximum of copper iodide cluster crystals are contributed by atomic orbitals from the inorganic core and organic ligand components, respectively. In addition to high scintillation performance, the as-prepared crystalline copper iodide cluster solids exhibit remarkable resistance toward both moisture and X-ray irradiation. These features allow copper iodide cluster scintillators to show particular attractiveness for low-dose X-ray radiography with a detection limit of 55  nGy s^-1 , a value ≈100 times lower than a standard dosage for X-ray examinations. The results suggest that optimizing both inorganic core and organic ligand for the building blocks of metal halide cluster crystals may provide new opportunities for a new generation of high-performance scintillation materials.

A versatile laboratory setup for high resolution X-ray phase contrast tomography and scintillator characterization

BACKGROUND

X-ray micro-tomography (μCT) is a powerful non-destructive 3D imaging method applied in many scientific fields. In combination with propagation-based phase-contrast, the method is suitable for samples with low absorption contrast. Phase contrast tomography has become available in the lab with the ongoing development of micro-focused tube sources, but it requires sensitive and high-resolution X-ray detectors. The development of novel scintillation detectors, particularly for microscopy, requires more flexibility than available in commercial tomography systems.

OBJECTIVE

We aim to develop a compact, flexible, and versatile μCT laboratory setup that combines absorption and phase contrast imaging as well as the option to use it for scintillator characterization. Here, we present details on the design and implementation of the setup.

METHODS

We used the setup for μCT in absorption and propagation-based phase-contrast mode, as well as to study a perovskite scintillator.

RESULTS

We show the 2D and 3D performance in absorption and phase contrast mode, as well as how the setup can be used for testing new scintillator materials in a realistic imaging environment. A spatial resolution of around 1.3μm is measured in 2D and 3D.

CONCLUSIONS

The setup meets the needs for common absorption μCT applications and offers increased contrast in phase contrast mode. The availability of a versatile laboratory μCT setup allows not only for easy access to tomographic measurements, but also enables a prompt monitoring and feedback beneficial for advances in scintillator fabrication.

Visualization of X-rays with an Ultralow Detection Limit via Zero-Dimensional Perovskite Scintillators

X-rays play an extremely significant role in medical diagnosis, safety testing, scientific research, and other practical applications. However, as the main sources of radioactive pollution, the hazard of X-rays to human health and the environment has been a major concern. Herein, the explored perovskite scintillator of Cs₂Zr_1-xPb_xCl₆ in this work exhibits an ultrahigh radioluminescence intensity owing to the enhanced X-ray absorption for the introduction of Pb²⁺ ions. The Cs₂Zr_1-xPb_xCl₆ crystals are demonstrated as efficient scintillators with a self-trapped exciton emission and extremely high steady-state light yield (∼101,944 photons meV^-1). This fascinating scintillator provides a convenient visual tool for X-ray detection even for an indoor lighting environment, reaching a low detection limit of ∼14.2 nGy·s^-1, which is about 1/387 of the typical medical imaging dose (5.5 μGy·s^-1). Moreover, X-ray imaging with a high resolution of 16.6 lp·mm^-1 is achieved with the as-explored Cs₂Zr_1-xPb_xCl₆ scintillator film. Herein, the Cs₂Zr_1-xPb_xCl₆ scintillator provides a feasible strategy for X-ray monitoring in the field of biomedicine, high-energy physics, national security, and other applications.

Scintillation Response of Nd-Doped LaMgAl11O19 Single Crystals Emitting NIR Photons for High-Dose Monitoring

The Nd-doped LaMgAl₁₁O₁₉ single crystals were synthesized by the floating zone method, and the photoluminescence and scintillation properties were evaluated. Under X-ray irradiation, several sharp emission peaks due to the 4f-4f transitions of Nd³⁺ were observed at 900, 1060, and 1340 nm in the near-infrared range, and the decay curves show the typical decay time for Nd³⁺. The samples show good afterglow properties comparable with practical X-ray scintillators. The 1% and 3% Nd-doped LaMgAl₁₁O₁₉ samples show a good linearity in the dynamic range from 6-60,000 mGy/h.

X-ray-Induced Scintillation Properties of Nd-Doped Bi4Si3O12 Crystals in Visible and Near-Infrared Regions

Undoped, 0.5, 1.0, and 2.0% Nd-doped Bi₄Si₃O₁₂ (BSO) crystals were synthesized by the floating zone method. Regarding photoluminescence (PL) properties, all samples had emission peaks due to the 6p-6s transitions of Bi³⁺ ions. In addition, the Nd-doped samples had emission peaks due to the 4f-4f transitions of Nd³⁺ ions as well. The PL quantum yield of the 0.5, 1.0, and 2.0% Nd-doped samples in the near-infrared range were 67.9, 73.0, and 56.6%, respectively. Regarding X-ray-induced scintillation properties, all samples showed emission properties similar to PL. Afterglow levels at 20 ms after X-ray irradiation of the undoped, 0.5, 1.0, and 2.0% Nd-doped samples were 192.3, 205.9, 228.2, and 315.4 ppm, respectively. Dose rate response functions had good linearity from 0.006 to 60 Gy/h for the 1.0% Nd-doped BSO sample and from 0.03 to 60 Gy/h for the other samples.

Compositionally Disordered Crystalline Compounds for Next Generation of Radiation Detectors

The review is devoted to the analysis of the compositional disordering potential of the crystal matrix of a scintillator to improve its scintillation parameters. Technological capabilities to complicate crystal matrices both in anionic and cationic sublattices of a variety of compounds are examined. The effects of the disorder at nano-level on the landscape at the bottom of the conduction band, which is adjacent to the band gap, have been discussed. The ways to control the composition of polycationic compounds when creating precursors, the role of disorder in the anionic sublattice in alkali halide compounds, a positive role of Gd based matrices on scintillation properties, and the control of the heterovalent state of the activator by creation of disorder in silicates have been considered as well. The benefits of introducing a 3D printing method, which is prospective for the engineering and production of scintillators at the nanoscale level, have been manifested.

Rose Bengal Decorated NaYF4:Tb Nanoparticles for Low Dose X-ray-Induced Photodynamic Therapy in Cancer Cells

The use of scintillating nanoparticles (ScNPs) in X-ray-induced photodynamic therapy (X-PDT) is a technique for deep tissue-localized tumor therapy with few side effects. ScNPs transfer X-ray-induced energy to photosensitizers, which generate massive amounts of reactive oxygen species (ROS) and kill cancer cells. Here we fabricated rose bengal (RB)-installed, Tb³⁺-rich NaYF₄ nanocrystals (NaYF₄:Tb@RB), in which optically inert Y³⁺ enables highly efficient energy transfer via high amounts of Tb³⁺ doping. NaYF₄:Tb was prepared via solvothermal synthesis to have an average size of 7.6 nm, followed by coating with poly(maleic anhydride-alt-1-octedecene)-poly(ethylene glycol) with a molecular weight of 2000 (C₁₈PMH-PEG_2k). Further, RB was covalently conjugated to carboxyl groups generated from PMH on NaYF₄:Tb using an ethylenediamine linker. NaYF₄:Tb@RB exhibited a hydrodynamic diameter of ∼75 nm with a ζ-potential of -12 mV. NaYF₄:Tb@RB efficiently generated ROS in cultured luciferase-expressing murine epithelial breast cancer (4T1-luc) cells under low dose X-ray irradiation (0.5 Gy). The ROS generation amounts of NaYF₄:Tb@RB were 1.5-2-fold higher than those of NaGdF₄:Tb@RB, in which host nanocrystals were prepared with optically active Gd³⁺. Flow cytometric and confocal microscopic analyses showed higher intracellular ROS production of NaYF₄:Tb@RB, compared to NaYF₄:Tb and RB, resulting in higher X-ray-induced DNA damage in cultured 4T1-luc cells. Ultimately, NaYF₄:Tb@RB elicited significant cytotoxicity after X-ray irradiation (0.5 Gy), while inducing marginal cytotoxicity without X-ray irradiation. Altogether, this research proposes a promising ScNP design for efficient X-PDT agents that make the better use of incident X-ray energy while causing the fewest side effects.

Micrometer-Resolution X-ray Imaging Enabled by a Flexible Perovskite Screen

Spatial resolution improvement has been keenly sought recently in the perovskite-based scintillation community. Here, micrometer resolution (∼2.0 μm) was achieved by using an X-ray imaging screen of self-assembled perovskite nanosheets. The assembly behavior of nanosheets was applicable to many substrates, including glass, metal, and polymer surfaces. The use of a polymer substrate not only eliminated the parasite absorption of X-ray but also enabled a flexible screen with robust bending stability. The assembly behavior, on the other hand, provided vicinity for an efficient energy transfer between nanosheets of varied thicknesses, as evidenced by both transient absorption and photoluminescence lifetime measurements. Importantly, the ensuing large Stokes shift (∼316 meV) significantly mitigated the reabsorption issue, leading to a comparable light yield to LYSO/Ce crystals. With the aid of the synchrotron-based collimated X-ray beam, the fine structure of two-dimensional objects, such as microchips, was clearly visualized with the flexible scintillation screen. Furthermore, those challenging biological samples were also scanned by phase-contrast imaging, whereby a three-dimensional reconstruction was obtained successfully. Despite the labile nature of the perovskite screen, this work represents the state-of-the-art spatial resolution for perovskite scintillation.

Visualization of dose distribution and basic study of dose estimation using plastic scintillator and digital camera

Radiation can be visualized using a scintillator and a digital camera. If the amount of light emitted by the scintillator increases with dose, the dose estimation can be obtained from the amount of light emitted. In this study, the basic performance of the scintillator and digital camera system was evaluated by measuring computed tomography dose index (CTDI). A circular plastic scintillator plate was sandwiched between polymethyl methacrylate (PMMA) phantoms, and X-rays were irradiated to them while rotating the X-ray tube to confirm changes in light emission. In addition, CTDI was estimated from the amount of light emitted by the scintillator during the helical scan and compared with the value measured from dosimeter. The scintillator emitted light while changing its distribution according to the movement of the X-ray tube. The measured CTDIvol was 33.20 mGy, the CTDIvol estimated from the scintillation light was approximately 46 mGy, which was 40% larger. In particular, when the scintillator was directly irradiated, the dose was overestimated compared with the value measured from the dosimeter. This overestimation can be because of the reproducibility of the position and the difference between the sensitivity of the scintillator to detect light emission and the sensitivity of the dosimeter, and the non-uniformity of position sensitivity due to the wide-angle lens.

Organic-Inorganic Hybrid Cuprous Halide Scintillators for Flexible X-ray Imaging

Recently, organic-inorganic hybrid scintillators have received more and more attention because of their merits of easy preparation, good stability, and nontoxicity. Considering the high cost of traditional inorganic scintillators, here we describe experimental investigations of a low-cost zero-dimensional scintillator comprising organic-inorganic hybrid cuprous halide and its capabilities for sensitive X-ray detection and flexible X-ray imaging. This scintillator is synthesized using a facile antisolvent diffusion method with large scalability (50 g). The crystal structure shows an unreported plane rhombus cuprous halide core, which also demonstrates outstanding photoluminescence with a high quantum yield (99.5%), excellent radioluminescence with an efficient internal light yield (25 000 photon/MeV), and sensitive X-ray response with a low detection limit (40.4 nGy/s). The organic-inorganic hybrid chemical feature allows the fabrication of a flexible film based on this scintillator for fine-resolution X-ray radiography. These advantages endow our organic-inorganic hybrid scintillator with promising potential in wearable and portable medical devices.

Wide Concentration Range of Tb3+ Doping Influence on Scintillation Properties of (Ce, Tb, Gd)3Ga2Al3O12 Crystals Grown by the Optical Floating Zone Method

To obtain a deeper understand of the energy transfer mechanism between Ce³⁺ and Tb³⁺ ions in the aluminum garnet hosts, (Ce, Tb, Gd)₃Ga₂Al₃O₁₂ (GGAG:Ce, Tb) single crystals grown by the optical floating zone (OFZ) method were investigated systematically in a wide range of Tb³⁺ doping concentration (1-66 at.%). Among those, crystal with 7 at.% Tb reached a single garnet phase while the crystals with other Tb³⁺ concentrations are mixed phases of garnet and perovskite. Obvious Ce and Ga loss can be observed by an energy dispersive X-ray spectroscope (EDS) technology. The absorption bands belonging to both Ce³⁺ and Tb³⁺ ions can be observed in all crystals. Photoluminescence (PL) spectra show the presence of an efficient energy transfer from the Tb³⁺ to Ce³⁺ and the gradually quenching effect with increasing of Tb³⁺ concentration. GGAG: 1% Ce³⁺, 7% Tb³⁺ crystal was found to possess the highest PL intensity under excitation of 450 nm. The maximum light yield (LY) reaches 18,941 pho/MeV. The improved luminescent and scintillation characteristics indicate that the cation engineering of Tb³⁺ can optimize the photoconversion performance of GGAG:Ce.

Quantum Shells Boost the Optical Gain of Lasing Media

Auger decay of multiple excitons represents a significant obstacle to photonic applications of semiconductor quantum dots (QDs). This nonradiative process is particularly detrimental to the performance of QD-based electroluminescent and lasing devices. Here, we demonstrate that semiconductor quantum shells with an "inverted" QD geometry inhibit Auger recombination, allowing substantial improvements to their multiexciton characteristics. By promoting a spatial separation between multiple excitons, the quantum shell geometry leads to ultralong biexciton lifetimes (>10 ns) and a large biexciton quantum yield. Furthermore, the architecture of quantum shells induces an exciton-exciton repulsion, which splits exciton and biexciton optical transitions, giving rise to an Auger-inactive single-exciton gain mode. In this regime, quantum shells exhibit the longest optical gain lifetime reported for colloidal QDs to date (>6 ns), which makes this geometry an attractive candidate for the development of optically and electrically pumped gain media.

Nanosecond and Highly Sensitive Scintillator Based on All-Inorganic Perovskite Single Crystals

The scintillator is a unique class of luminescent materials, which is of great significance in clinical diagnosis, security inspection, and radiation detection. Herein, an all-inorganic Cs₄PbI₆ single crystals (SCs) as a nanosecond and an efficient X-ray and α particle scintillator is described. The radioluminescence (RL) spectrum of Cs₄PbI₆ SCs under X-ray excitation consists of a band gap emission at 310 nm and a broadband emission at 552 nm at room temperature. Furthermore, Cs₄PbI₆ SCs demonstrate nanosecond decay times of 0.95 and 6.86 ns, a high sensitivity to low-energy X-ray (30 keV) with a low detection limit (187 nGy_air/s), and a favorable linearity detection range, potentially enabling their broad application in X-ray imaging. Under ²³⁷Np α particle irradiation, the light yield of Cs₄PbI₆ SCs is about 49.5% of that of a BGO scintillator with an energy resolution of 35% at 4.78 MeV. Our results demonstrate the potential of Cs₄PbI₆ SCs as a nanosecond and low-cost scintillator in radiation detection applications.

Replacing gamma knife beam-profiles on film with point-detector scans

PURPOSE

Detector arrays and profile-scans have widely replaced film-measurements for quality assurance (QA) on linear accelerators. Film is still used for relative output factor (ROF) measurements, positioning, and dose-profile verification for annual Leksell Gamma Knife (LGK) QA. This study shows that small-field active detector measurements can be performed in the easily accessed clinical mode and that they are an effective replacement to time-consuming and exacting film measurements.

METHODS

Beam profiles and positioning scans for 4-mm, 8-mm, and 16-mm-collimated fields were collected along the x-, y-, and z-axes. The Exradin W2-scintillator and the PTW microdiamond-detector were placed in custom inserts centered in the Elekta solid-water phantom for these scans. GafChromic EBT3-film was irradiated with single uniformly collimated exposures as the clinical-standard reference, using the same solid-water phantom for profile tests and the Elekta film holder for radiation focal point (RFP)/patient-positioning system (PPS) coincidence. All experimental data were compared to the tissue-maximum-ratio-based (TMR10) dose calculation.

RESULTS

The detector-measured beam profiles and film-based profiles showed excellent agreement with TMR10-predicted full-width, half-maximum (FWHM) values. Absolute differences between the measured FWHM and FWHM from the treatment-planning system were on average 0.13 mm, 0.08 mm, and 0.04 mm for film, microdiamond, and scintillator, respectively. The coincidence between the RFP and the PPS was measured to be ≤0.5 mm with microdiamond, ≤0.41 mm with the W2-1 × 1 scintillator, and ≤0.22 mm using the film-technique.

CONCLUSIONS

Small-volume field detectors, used in conjunction with a clinically available phantom, an electrometer with data-logging, and treatment plans created in clinical mode offer an efficient and viable alternative for film-based profile tests. Position verification can be accurately performed when CBCT-imaging is available to correct for residual detector-position uncertainty. Scans are easily set up within the treatment-planning-system and, when coupled with an automated analysis, can provide accurate measurements within minutes.

Comparison of photon transport efficiency in simple scintillation electron detector configurations for scanning electron microscope

The purpose of this paper is to find some general rules for the design of robust scintillation electron detectors for a scanning electron microscope (SEM) that possesses an efficient light-guiding (LG) system. The paper offers some general instructions on how to avoid the improper design of highly inefficient LG configurations of the detectors. Attention was paid to the relevant optical properties of the scintillator, light guide, and other components used in the LG part of the scintillation detector. Utilizing the optical properties of the detector components, 3D Monte Carlo (MC) simulations of photon transport efficiency in the simple scintillation detector configurations were performed using the computer application called SCIUNI to assess shapes and dimensions of the LG part of the detector. The results of the simulation of both base-guided signal (BGS) configurations for SE detection and edge-guided signal (EGS) configurations for BSE detection are presented. It is demonstrated that the BGS configuration with a matted disc scintillator exit side connected to the cylindrical light guide without optical cement is almost always a sufficiently efficient system with a mean LG efficiency of about 20%. It is simulated that poorly designed EGS strip configurations have an extremely low mean LG efficiency of only 0.01%, which can significantly reduce detector performance. On the other hand, no simple nonoptimized EGS configuration with a light guide widening to a circular or square profile, with a polished cemented scintillator and with an indispensable hole in it has a mean LG efficiency lower than 6.5%.

Size-Dependent Nonlinear Optical Properties of Gd2O2S:Tb3+ Scintillators and Their Doped Gel Glasses

With the advancement of ultra-fast and high-energy pulsed laser output, lasers have caused serious harm to precision instruments and human eyes. Therefore, the development of optical limiting materials with a fast response, low optical limiting threshold, and high damage threshold are important. In this work, for the first time, it is reported that phosphors Gd₂O₂S:Tb³⁺(GOS) displays exceptional functionality in laser protection. GOS with sizes of 11 μm, 1 μm, and 0.45 μm are prepared. Based on the optical limiting and Z-scan technology systems under 532 nm and 1064 nm nanosecond laser excitation, the nonlinear optical properties of GOS are investigated. It is found that GOS exhibits outstanding optical limiting properties. In addition, the optical limiting response of GOS is size-dependent. Concerning the largest particle size, GOS has the best nonlinear optical response, while the precursor shows no nonlinear optical performance. Meanwhile, GOS doped gel glass also displays excellent optical limiting properties with high transmittance, which preliminarily validates the application of GOS and other scintillators in nonlinear optics and encourages more research to better realize the potential of GOS.

Scintillation Response Enhancement in Nanocrystalline Lead Halide Perovskite Thin Films on Scintillating Wafers

Lead halide perovskite nanocrystals of the formula CsPbBr₃ have recently been identified as potential time taggers in scintillating heterostructures for time-of-flight positron emission tomography (TOF-PET) imaging thanks to their ultrafast decay kinetics. This study investigates the potential of this material experimentally. We fabricated CsPbBr₃ thin films on scintillating GGAG:Ce (Gd_2.985Ce_0.015Ga_2.7Al_2.3O₁₂) wafer as a model structure for the future sampling detector geometry. We focused this study on the radioluminescence (RL) response of this composite material. We compare the results of two spin-coating methods, namely the static and the dynamic process, for the thin film preparation. We demonstrated enhanced RL intensity of both CsPbBr₃ and GGAG:Ce scintillating constituents of a composite material. This synergic effect arises in both the RL spectra and decays, including decays in the short time window (50 ns). Consequently, this study confirms the applicability of CsPbBr₃ nanocrystals as efficient time taggers for ultrafast timing applications, such as TOF-PET.

Stable and Bright Commercial CsPbBr3 Quantum Dot-Resin Layers for Apparent X-ray Imaging Screen

CsPbBr₃ quantum dots (QDs) have recently gained much interest due to their excellent optical and scintillation properties and their potential for X-ray imaging applications. In this study, we blended CsPbBr₃ QDs with resin at different QD concentrations to achieve thick films and to protect the CsPbBr₃ QDs from environmental moisture. Then, their scintillation properties are investigated and compared to the traditional commercial scintillators, CsI:Tl microcolumns, and Gadox layers. The CsPbBr₃ QD-resin sheets show a high light yield of up to 21 500 photons/MeV at room temperature and a relatively small variation in light yield across a wide temperature range. In addition, the CsPbBr₃ QD-resin sheets feature a small scintillation afterglow. The CsPbBr₃ QD-resin sheets show a negligible trap density for the concentration below 50% weight, indicating that traps might arise from the aggregation of the QDs. The CsPbBr₃ QD-resin sheets are also very stable at low irradiation intensities and relatively stable at higher intensities, with higher CsPbBr₃ QD concentrations being more stable. Gamma-ray-excited-time-resolved emission measurements at 662 keV showed that the CsPbBr₃ QD-resin sheets have an average scintillation decay time between 108 and 176 ns, which are still 10 000 and 6000 times faster than CsI:Tl and Gadox, respectively. Imaging tests show that the CsPbBr₃ QD-resin sheets have a mean transfer function of 50% at 2 lp/mm and 20% at 4 lp/mm, comparable to that of commercial Gadox layers. This feature makes CsPbBr₃ QD-resin sheets a good candidate for the low-cost, flexible X-ray imaging screens and γ-ray applications.

Remote Optogenetics Using Up/Down-Conversion Phosphors

Microbial rhodopsins widely used for optogenetics are sensitive to light in the visible spectrum. As visible light is heavily scattered and absorbed by tissue, stimulating light for optogenetic control does not reach deep in the tissue irradiated from outside the subject body. Conventional optogenetics employs fiber optics inserted close to the target, which is highly invasive and poses various problems for researchers. Recent advances in material science integrated with neuroscience have enabled remote optogenetic control of neuronal activities in living animals using up- or down-conversion phosphors. The development of these methodologies has stimulated researchers to test novel strategies for less invasive, wireless control of cellular functions in the brain and other tissues. Here, we review recent reports related to these new technologies and discuss the current limitations and future perspectives toward the establishment of non-invasive optogenetics for clinical applications.

High Photoluminescence Quantum Yield Perovskite/Polymer Nanocomposites for High Contrast X-ray Imaging

A surface modified-CsPbBr₃/polybutylmethacrylate (PBMA) nanocomposite is reported to be a scintillator that enables us to provide a high contrast X-ray image using a common charge-coupled device (CCD) camera. Bis(2-(methacryloyloxy)ethyl) phosphate (BMEP) was employed to alter the ratio of the original ligands on the CsPbBr₃ nanocrystal (NC) surface for optimizing the optical performance of the CsPbBr₃/PBMA nanocomposites. The nanocomposites with a concentration of 0.02 wt % NCs exhibit more than 70% transmittance in the visible region and show a green emission at 515 nm, the fast decay time is 13 ns, while the photoluminescence quantum yield value is 99.2%. Under X-ray excitation, the emission peak wavelength is centered at 524 nm and shows a narrow full width at half-maximum of 26.6 nm; the result nicely matches with the peak quantum efficiency of most commercial CCD/complementary metal oxide semiconductor cameras. The high contrast X-ray image is recorded at a low dose rate of 4.6 μGy_air/s, which enables read out with software. Our results demonstrate that these CsPbBr₃/PBMA nanocomposites have promising application prospects for ionizing radiation detection, especially for X-ray imaging.

Simulating 50 keV X-ray Photon Detection in Silicon with a Down-Conversion Layer

Simulation results are presented that explore an innovative, new design for X-ray detection in the 20-50 keV range that is an alternative to traditional direct and indirect detection methods. Typical indirect detection using a scintillator must trade-off between absorption efficiency and spatial resolution. With a high-Z layer that down-converts incident photons on top of a silicon detector, this design has increased absorption efficiency without sacrificing spatial resolution. Simulation results elucidate the relationship between the thickness of each layer and the number of photoelectrons generated. Further, the physics behind the production of electron-hole pairs in the silicon layer is studied via a second model to shed more light on the detector's functionality. Together, the two models provide a greater understanding of this detector and reveal the potential of this novel form of X-ray detection.

Effect of Ceramic Formation on the Emission of Eu3+ and Nd3+ Ions in Double Perovskites

Herein, the structure, morphology, as well as optical properties of the powder and ceramic samples of Ba2MgWO6 are presented. Powder samples were obtained by high temperature solid-state reaction, while, for the ceramics, the SPS technique under 50-MPa pressure was applied. The morphology of the investigated samples showed some agglomeration and grains with a submicron size of 490-492 µm. The theoretical density and relative density of ceramics were calculated using the Archimedes method. The influence of sample preparation on the position, shape, and character of the host, as well as dopants emission was investigated. Sample sintering enhances regular emission of WO6 groups causing a blue shift of Ba2MgWO6 emission. Nonetheless, under X-ray excitation, only the green emission of inversion WO6 group was detected. For the ceramic doped with Eu3+ ions, the emission of both host and dopant was detected. However, for the powder efficient host to activator energy, the transfer process occurred, and only the magnetic dipole emission of Eu3+ was detected. The intensity of Nd3+ ions of Ba2MgWO6 powder sample is five times higher than for the ceramic. The sintering process reduces inversion defects and creates a highly symmetrical site of neodymium ions. The emission of Ba2MgWO6:Nd3+ consists of transitions from the 4F3/2 excited level to the 4IJ multiplet states with the dominance of the 4F3/2→4I11/2 one. The spectroscopic quality parameter and branching ratio of Nd3+ emission are presented.

Highly Resolved and Robust Dynamic X-Ray Imaging Using Perovskite Glass-Ceramic Scintillator with Reduced Light Scattering

All-inorganic perovskite quantum dots (QDs) CsPbX3 (X = Cl, Br, and I) have recently emerged as a new promising class of X-ray scintillators. However, the instability of perovskite QDs and the strong optical scattering of the thick opaque QD scintillator film imped it to realize high-quality and robust X-ray image. Herein, the europium (Eu) doped CsPbBr3 QDs are in situ grown inside transparent amorphous matrix to form glass-ceramic (GC) scintillator with glass phase serving as both matrix and encapsulation for the perovskite QD scintillators. The small amount of Eu dopant optimizes the crystallization of CsPbBr3 QDs and makes their distribution more uniform in the glass matrix, which can significantly reduce the light scattering and also enhance the photoluminescence emission of CsPbBr3 QDs. As a result, a remarkably high spatial resolution of 15.0 lp mm-1 is realized thanks to the reduced light scattering, which is so far a record resolution for perovskite scintillator based X-ray imaging, and the scintillation stability is also significantly improved compared to the bare perovskite QD scintillators. Those results provide an effective platform particularly for the emerging perovskite nanocrystal scintillators to reduce light scattering and improve radiation hardness.

Nanomaterials for Deep Tumor Treatment

According to statistics, cancer is the second leading cause of death in the world. Thus, it is important to solve this medical and social problem by developing new effective methods for cancer treatment. An alternative to more well-known approaches, such as radiotherapy and chemotherapy, is photodynamic therapy (PDT), which is limited to the shallow tissue penetration (< 1 cm) of visible light. Since the PDT process can be initiated in deep tissues by X-ray irradiation (X-ray induced PDT, or XPDT), it has a great potential to treat tumors in internal organs. The article discusses the principles of therapies. The main focus is on various nanoparticles used with or without photosensitizers, which allow the conversion of X-ray irradiation into UV-visible light. Much attention is given to the synthesis of nanoparticles and analysis of their characteristics, such as size and spectral features. The results of in vitro and in vivo experiments are also discussed.

Image quality evaluation of projection- and depth dose-based approaches to integrating proton radiography using a monolithic scintillator detector

The purpose of this study is to compare the image quality of an integrating proton radiography (PR) system, composed of a monolithic scintillator and two digital cameras, using integral lateral-dose and integral depth-dose image reconstruction techniques. Monte Carlo simulations were used to obtain the energy deposition in a 3D monolithic scintillator detector (30 × 30 × 30 cm³poly vinyl toluene organic scintillator) to create radiographs of various phantoms-a slanted aluminum cube for spatial resolution analysis and a Las Vegas phantom for contrast analysis. The light emission of the scintillator was corrected using Birks scintillation model. We compared two integrating PR methods and the expected results from an idealized proton tracking radiography system. Four different image reconstruction methods were utilized in this study: integral scintillation light projected from the beams-eye view, depth-dose based reconstruction methods both with and without optimization, and single particle tracking PR was used for reference data. Results showed that heterogeneity artifact due to medium-interface mismatch was identified from the Las Vegas phantom simulated in air. Spatial resolution was found to be highest for single-event reconstruction. Contrast levels, ranked from best to worst, were found to correspond to particle tracking, optimized depth-dose, depth-dose, and projection-based image reconstructions. The image quality of a monolithic scintillator integrating PR system was sufficient to warrant further exploration. These results show promise for potential clinical use as radiographic techniques for visualizing internal patient anatomy during proton radiotherapy.

Silicon photomultiplier-based scintillation detectors for photon-counting CT: A feasibility study

PURPOSE

The implementation of photon-counting detectors is widely expected to be the next breakthrough in X-ray computed tomography (CT) instrumentation. A small number of prototype scanners equipped with direct-conversion detectors based on room-temperature semiconductors, such as CdTe and CdZnTe (CZT), are currently installed at medical centers. Here, we investigate the feasibility of using silicon photomultiplier (SiPM)-based scintillation detectors in photon-counting computed tomography (PCCT) scanners, as a potential alternative to CdTe and CZT detectors.

METHODS

We introduce a model that allows us to compute the expected energy resolution as well as the expected pulse shape and associated rate capability of SiPM-based PCCT detectors. The model takes into account SiPM saturation and optical crosstalk, because these phenomena may substantially affect the performance of SiPM-based PCCT detectors with sub-mm pixels. We present model validation experiments using a single-pixel detector consisting of a 0.9 × 0.9 × 1.0 mm³ LuAP:Ce scintillation crystal coupled to a 1 × 1 mm² SiPM. We subsequently use the validated model to compute the expected performance of the fast scintillators LYSO:Ce, LuAP:Ce, and LaBr₃ :Ce, coupled to currently available SiPMs, as well as to a more advanced SiPM prototype with improved dynamic range, for sub-mm pixel sizes.

RESULTS

The model was found to be in good agreement with the validation experiments, both with respect to energy resolution and pulse shape. It shows how saturation progressively degrades the energy resolution of detectors equipped with currently available SiPMs as the pixel size decreases. Moreover, the expected pulse duration is relatively long (~200 ns) with these SiPMs. However, when LuAP:Ce and LaBr₃ :Ce are coupled to the more advanced SiPM prototype, the pulse duration improves to less than 60 ns, which is in the same order of magnitude as pulses from CdTe and CZT detectors. It follows that sufficient rate capability can be achieved with pixel sizes of 400 μm or smaller. Moreover, LaBr₃ :Ce detectors can provide an energy resolution of 11.5%-13.5% at 60 keV, comparable to CdTe and CZT detectors.

CONCLUSIONS

This work provides first evidence that it may be feasible to develop SiPM-based scintillation detectors for PCCT that can compete with CdTe and CZT detectors in terms of energy resolution and rate capability.

Feasibility of cerium-doped LSO particles as a scintillator for x-ray induced optogenetics

Objective.Non-invasive light delivery into the brain is needed forin vivooptogenetics to avoid physical damage. An innovative strategy could employ x-ray activation of radioluminescent particles (RLPs) to emit localized light. However, modulation of neuronal or synaptic function by x-ray induced radioluminescence from RLPs has not yet been demonstrated.Approach.Molecular and electrophysiological approaches were used to determine if x-ray dependent radioluminescence emitted from RLPs can activate light sensitive proteins. RLPs composed of cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light, were used as they are biocompatible with neuronal function and synaptic transmission.Main results.We show that 30 min of x-ray exposure at a rate of 0.042 Gy s-1caused no change in the strength of basal glutamatergic transmission during extracellular field recordings in mouse hippocampal slices. Additionally, long-term potentiation, a robust measure of synaptic integrity, was induced after x-ray exposure and expressed at a magnitude not different from control conditions (absence of x-rays). We found that x-ray stimulation of RLPs elevated cAMP levels in HEK293T cells expressing OptoXR, a chimeric opsin receptor that combines the extracellular light-sensitive domain of rhodopsin with an intracellular second messenger signaling cascade. This demonstrates that x-ray radioluminescence from LSO:Ce particles can activate OptoXR. Next, we tested whether x-ray activation of the RLPs can enhance synaptic activity in whole-cell recordings from hippocampal neurons expressing channelrhodopsin-2, both in cell culture and acute hippocampal slices. Importantly, x-ray radioluminescence caused an increase in the frequency of spontaneous excitatory postsynaptic currents in both systems, indicating activation of channelrhodopsin-2 and excitation of neurons.Significance.Together, our results show that x-ray activation of LSO:Ce particles can heighten cellular and synaptic function. The combination of LSO:Ce inorganic scintillators and x-rays is therefore a viable method for optogenetics as an alternative to more invasive light delivery methods.

Basic study of mobile gamma ray imaging using a digital camera and scintillator

Gamma cameras are used in nuclear medicine examinations involving radioisotopes; however, they do not provide real-time feedback. We propose a real-time imaging method based on a commercially available digital camera and a scintillator array to provide simple and accurate measurements of radioisotope accumulation and contamination. We evaluate the sensitivity and resolution of the proposed device using X-rays as a proxy for gamma-rays. The performance of the device is demonstrated using PENTAX KP and ORCA-spark C11440-36U digital cameras. A caesium iodide scintillator array is irradiated with X-rays, with the state of light emission confirmed using live view images. The pixel value is evaluated as a function of dose rate. Furthermore, we investigate the state of light emission in response to amplifying the light signal using an image intensifier. For the PENTAX KP, luminescence is observable for a dose rate of approximately 10 mSv/h, which changes to 2.1 mSv/h when an image intensifier is used. Notably, the ORCA-spark detected emission at a low dose rate of 0.06 mSv/h. However, using an image intensifier resulted in noisier images. Therefore, although the ORCA-spark can observe luminescence at a suitable predicted dose rate for application in nuclear medicine examinations, a collimator is required to control the spread of gamma rays. However, as this causes the sensitivity to decrease, increasing the amount of light emitted by the scintillator and improving the sensitivity of the camera is vital.

Non-Hygroscopic, Self-Absorption Free, and Efficient 1D CsCu2I3 Perovskite Single Crystal for Radiation Detection

A novel all-inorganic CsCu₂I₃ single-crystalline perovskite as a nonhygroscopic and efficient X-ray and γ-ray scintillator is described herein. It is featured by a one-dimensional (1D) perovskite structure with an orthorhombic system and a space group of Cmcm. The CsCu₂I₃ crystal emits yellow light peaking at 570 nm originated from strongly localized 1D exciton emission. It appears self-absorption free because of the large Stokes shift of 1.54 eV. The photophysics process of the self-trapped exciton was studied using temperature dependent photoluminescene spectra and decay kinetics measurements. The CsCu₂I₃ crystal exhibits an extremely low afterglow level of 0.008% at 10 ms under X-ray excitation. Under ¹³⁷Cs γ-ray irradiation, its light yield is 16 000 photons/MeV with an energy resolution of 7.8% at 662 keV.

Oriented-Structured CsCu2I3 Film by Close-Space Sublimation and Nanoscale Seed Screening for High-Resolution X-ray Imaging

An all-inorganic lead-free halides Cs-Cu-I system, represented by Cs₃Cu₂I₅ and CsCu₂I₃, has attracted attention for their good photophysical characteristics recently. Successive works had reported their application potential in light-emitting devices. However, there is no report for CsCu₂I₃ in X-ray scintillation detectors so far. We notice that CsCu₂I₃ may be advantageous in such an application due to the one-dimensional crystal structure, the congruent-melting feature, and the high spectral matching to some photosensors. In this work, we explore the scintillation properties and imaging application of CsCu₂I₃ in X-ray scintillator detector. The oriented structure is designed to enhance the imaging performance of a CsCu₂I₃ detector. Close-space sublimation process and nanoscale seed screening strategy are employed to realize this design by producing a large-area (25 cm²) CsCu₂I₃ thick film layer with the oriented nanorod structure. This CsCu₂I₃ detector eventually achieves a high spatial resolution of 7.5 lp mm^-1 in X-ray imaging.

The crystal structure of TlMgCl3 from 290 K to 725 K

The title compound, thallium magnesium trichloride, has been identified as a scintillator with both moderate gamma-stopping power and moderate light yield. Knowledge of its crystal structure is needed for further development. This work determines the crystal structure of TlMgCl₃ to be hexa­gonal P6₃/mmc (No. 194) and isostructural with RbMgCl₃, contrary to previously reported data. Extending neutron diffraction measurements to high temperature, the data show that TlMgCl₃ maintains this crystal structure from 290 K up through 725 K, approaching the melting point of 770 K.

The title compound, thallium magnesium trichloride, has been identified as a scintillator with both moderate gamma-stopping power and moderate light yield. Knowledge of its crystal structure is needed for further development. This work determines the crystal structure of TlMgCl₃ to be hexa­gonal P6₃/mmc (No. 194) and isostructural with RbMgCl₃, contrary to previously reported data. This structure was obtained by single-crystal X-ray diffraction and was further confirmed by neutron diffraction measurements. Extending neutron diffraction measurements to high temperature, the data show that TlMgCl₃ maintains this crystal structure from 290 K up through 725 K, approaching the melting point of 770 K. Anisotropic thermal expansion coefficients increase over this temperature range, from 31 to 38 × 10⁻⁶ K⁻¹ along the a axis and from 19 to 34 × 10⁻⁶ K⁻¹ along the c axis.

Characterization of a Low-Cost Plastic Fiber Array Detector for Proton Beam Dosimetry

The Pencil Beam Scanning (PBS) technique in proton therapy uses fast magnets to scan the tumor volume rapidly. Changing the proton energy allows changing to layers in the third dimension, hence scanning the same volume several times. The PBS approach permits adapting the speed and/or current to modulate the delivered dose. We built a simple prototype that measures the dose distribution in a single step. The active detection material consists of a single layer of scintillating fibers (i.e., 1D) with an active length of 100 mm, a width of 18.25 mm, and an insignificant space (20 μm) between them. A commercial CMOS-based camera detects the scintillation light. Short exposure times allow running the camera at high frame rates, thus, monitoring the beam motion. A simple image processing method extracts the dose information from each fiber of the array. The prototype would allow scaling the concept to multiple layers read out by the same camera, such that the costs do not scale with the dimensions of the fiber array. Presented here are the characteristics of the prototype, studied under two modalities: spatial resolution, linearity, and energy dependence, characterized at the Center for Proton Therapy (Paul Scherrer Institute); the dose rate response, measured at an electron accelerator (Swiss Federal Institute of Metrology).

Prismatoid light guide array for enhanced gamma ray localization in PET: a Monte Carlo simulation study of scintillation photon transport

High spatial resolution PET relies on having excellent depth-of-interaction (DOI) resolution and small detector elements. Depth-encoding in PET modules has traditionally been performed using dual-ended readout. In recent years, researchers have explored the feasibility of replacing the second readout array with a light guide at the entrance layer that introduces intercrystal light sharing in order to reduce cost and and make depth-encoding modules more compact. However, single-ended readout depth-encoding modules have suboptimal and non-uniform crystal separation and DOI performance due to the random light sharing patterns of the uniform light guide, resulting in degraded peformance along the edges and corners of the detector arrays. In this paper, we introduce and characterize a segmented light guide composed of an array of prism mirrors which introduce deterministic intercrystal light sharing in single-ended readout PET detectors. We determined the expected spatial performance of our modules with our light guide using optical ray tracing Monte Carlo simulations. We demonstrate that having controlled, deterministic light sharing improves both DOI and crystal identification performance, enabling uniform spatial performance throughout the detector array. Designed specifically for high resolution PET, our prismatoid light guide array can be used to build cost-effective total-body and organ-dedicated PET systems with single-ended readout depth-encoding modules.