Low-energy Photons Research Articles

Efficient and Robust Europium(III)-Based Hybrid Lanthanide Scintillators for Advanced X-Ray Imaging.

Scintillators that convert ionizing radiation into low-energy photons are essential for medical diagnostics and industrial inspections. Despite advances in X-ray scintillators, challenges remain in achieving high efficiency, environmental compatibility, stability, and flexibility. Here, we present experimental investigations of a new type of europium(III)-based hybrid ternary complex scintillators for improved X-ray detection and imaging. Benefiting from the synergistic interaction between dual organic ligands and lanthanide ions, the Eu(TTA)3Phen complex demonstrates exceptional radioluminescence and light yield under X-ray excitation, with a detection limit of 19.97 nGy s-1, well below typical radiation doses used in medical diagnostics. Moreover, lanthanide complex Eu(TTA)3Phen exhibited excellent thermal and photostability, showing minimal degradation even after extended X-ray exposure. By integrating with flexible polymer matrices, a high-transmission Eu(TTA)3Phen-PMMA composite film was fabricated for X-ray radiography, demonstrating high spatial resolution (<10 um) and superior image quality across various target samples. These findings hold substantial promise for next-generation X-ray imaging applications, offering high sensitivity, stability, flexibility, and versatility, making them ideally suited for advanced radiographic systems.

Simulations of the Potential for Diffraction Enhanced Imaging at 8 keV using Polycapillary Optics.

Conventional x-ray radiography relies on attenuation differences in the object, which often results in poor contrast in soft tissues. X-ray phase imaging has the potential to produce higher contrast but can be difficult to utilize. Instead of grating-based techniques, analyzer-based imaging, also known as diffraction enhanced imaging (DEI), uses a monochromator crystal with an analyzer crystal after the object. Analyzer-based systems most commonly employ synchrotron sources to provide adequate intensity, and typically use higher photon energies. In this work, a simulation has been devised to assess the potential for a polycapillary-based system. The collimating optic has previously been shown to greatly enhance the intensity of the beam diffracted from the monochromatizing crystal. Detailed simulation of the optic is computationally intensive and requires comprehensive knowledge of the optic internal shape, so a simple geometric model using easier to obtain optic output data was developed and compared to the more detailed simulation. After verification, refraction band visibility was used as a quality parameter to address the effectiveness of the polycapillary-based DEI system at x-ray photon energies of 8 and 17.5 keV. The result shows promise for a polycapillary-coupled analyzer-based system even at low x-ray photon energy.

Sub-bandgap charge harvesting and energy up-conversion in metal halide perovskites: ab initio quantum dynamics

Metal halide perovskites (MHPs) exhibit unusual properties and complex dynamics. By combining ab initio time-dependent density functional theory, nonadiabatic molecular dynamics and machine learning, we advance quantum dynamics simulation to nanosecond timescale and demonstrate that large fluctuations of MHP defect energy levels extend light absorption to longer wavelengths and enable trapped charges to escape into bands. This allows low energy photons to contribute to photocurrent through energy up-conversion. Deep defect levels can become shallow transiently and vice versa, altering the traditional defect classification into shallow and deep. While defect levels fluctuate more in MHPs than traditional semiconductors, some levels, e.g., Pb interstitials, remain far from band edges, acting as charge recombination centers. Still, many defects deemed detrimental based on static structures, are in fact benign and can contribute to energy up-conversion. The extended light harvesting and energy up-conversion provide strategies for design of novel solar, optoelectronic, and quantum information devices.

Multispectral Integrated Black Arsenene Phototransistors for High-Resolution Imaging and Enhanced Secure Communication.

The demand for broadband, room-temperature infrared, and terahertz (THz) detectors is rapidly increasing owing to crucial applications in telecommunications, security screening, nondestructive testing, and medical diagnostics. Current photodetectors face significant challenges, including high intrinsic dark currents and the necessity for cryogenic cooling, which limit their effectiveness in detecting low-energy photons. Here, we introduce a high-performance ultrabroadband photodetector operating at room temperature based on two-dimensional black arsenene (b-As) nanosheets. This device demonstrates responsivity across visible, near-infrared, and THz spectral ranges, with responsivities reaching 91.6 A/W at 520 nm, 6.3 A/W at 1550 nm, and 7.8 V/W at 0.27 THz. The exceptional THz responsivity is attributed to the use of plasma-wave rectification in antenna-integrated field-effect transistors with asymmetric antennas, enhancing light-matter interaction and facilitating nonlinear rectification within the two-dimensional electron gas of the transistor channel, achieving a voltage-dependent bipolar response. These advanced b-As-based photodetectors also enable secure THz communication through complex logic operations, achieving robust data encryption and high-performance signal processing.

Understanding the Variations of Optical Bandgap in AZO Nanostructured Thin Films: Analysis of Possible Influences

Aluminum doped zinc oxide (AZO) thin films with varying thicknesses are fabricated using radio frequency (RF) sputtering combined with substrate rotation. The films display distinct nanocolumnar structures characterized by a hexagonal ZnO phase and a noticeable shift of the primary diffraction peak to lower 2θ angles. Lattice parameters a and c are used to evaluate residual stress and structural relaxation, both of which vary with increasing film thickness. Despite these structural changes, the films consistently maintain an average optical transmittance close to 85% in the range of 400–900 nm. The absorption edge and bandgap energy shift toward lower photon energies, decreasing from 3.51 to 3.38 eV as the thickness increases. The interplay between residual stress, structural relaxation, and bandgap energy is analyzed, offering insights into the complex dynamics influencing AZO thin‐film fabrication and the potential effects of quantum confinement. Lastly, the findings are compared with recent studies on ZnO thin films.

First-order perturbative estimate of the d+t+γ→α+n reaction rate

A new type of photoinduced nuclear reactions is considered when a photon is absorbed by a continuum state and accompanied by nuclear rearrangement. An important example of such reactions is d+t+γ→α+n which, in the regions of space containing a hot d−t mixture and a very large number of low-energy photons, can dominate the d+t→α+n fusion reaction, leading to an additional high-energy release. The present estimates of the environmental conditions where this might happen are made based on first-order perturbation theory with several values of the infrared cutoff. It is shown that with a cutoff of 1 eV, which corresponds to infrared light, the photon capture is several times larger than the d−t fusion rate in the big bang nucleosynthesis in the early universe, makes a noticeable contribution to energy release in tokamaks, and dominates by a few orders of magnitude in laser-direct-driven inertial confinement fusion. No effect on these three environments can be seen if the infrared cutoff is 1 keV. However, with this cutoff the photon absorption in a d−t mixture could become noticeable in future laser facilities at power intensities above 1018Watt/cm2. With further increase of the intensity towards 1027Watt/cm2 photon capture will dominate even if the first-order perturbation theory breaks down at very large values of the infrared cutoff, around 1 MeV. The development of a nonperturbative approach to d+t+γ→α+n reaction is crucial to capture correctly the physics of low-energy photoabsorption with high-energy release. Published by the American Physical Society 2024

Spectral Energy Distribution Modeling of BL Lacertae during a Large Submillimeter Outburst and Low X-Ray Polarization State

Abstract In 2023 October–November, the blazar BL Lacertae underwent a very large-amplitude submillimeter outburst. The usual single-zone leptonic model with the lower-energy peak of the spectral energy distribution (SED) fit by the synchrotron emission from one distribution of relativistic electrons in the jet and inverse-Compton (IC) scattering of lower-energy photons from the synchrotron radiation in the jet itself (synchrotron self-Compton or SSC) or those from the broad-line region and torus by the same distribution of electrons cannot satisfactorily fit the broadband SED with simultaneous data at submillimeter, optical, X-ray, and GeV energies. Furthermore, simultaneous observations with IXPE indicate the X-ray polarization is undetected. We consider two different synchrotron components, one for the high flux in the submillimeter wavelengths and another for the data at the optical band, which are supposedly due to two separate distributions of electrons. In that case, the optical emission is dominated by the synchrotron radiation from one electron distribution, while the X-rays are mostly due to SSC process by another, which may result in low polarization fraction due to the IC scattering. We show that such a model can fit the broadband SED satisfactorily as well as explain the low polarization fraction at the X-rays.

Unambiguous Detection of High-Energy Vortex States via the Superkick Effect

Vortex states of photons, electrons, and other particles are freely propagating wave packets with helicoidal wave fronts winding around the axis of a phase vortex. A particle prepared in a vortex state carries a nonzero orbital angular momentum projection on the propagation direction, a quantum number that has never been exploited in experimental particle and nuclear physics. Low-energy vortex photons, electrons, neutrons, and helium atoms have been demonstrated in experiment and found numerous applications, and there exist proposals of boosting them to higher energies. However, verification that a high-energy particle is indeed in a vortex state will be a major challenge, since the low energy techniques become impractical at higher energies. Here, we propose a new diagnostic method based on the so-called superkick effect, which can unambiguously detect the presence of a phase vortex. A proof-of-principle experiment with vortex electrons can be done with existing technology, and its realization will also constitute the first observation of the superkick effect. Published by the American Physical Society 2024

The clinical applications of dual-layer spectral detector CT in digestive system diseases.

Dual-layer spectral detector CT (DLCT) has several advantages in clinical practice, this study aims to reveal the clinical applications of DLCT in digestive system diseases. We searched PubMed and Cochrane Reviews for articles published from January 1, 2010 to May 31, 2024, using the terms "dual-layer spectral detector CT" or "dual-layer CT" combined with "hepatic fat" or "hepatic fibrosis" "hepatocellular carcinoma" or "pancreatic ductal adenocarcinoma" or "pancreatic neuroendocrine tumors" or "gastric cancer" or "colorectal cancer" or "Crohn's disease" or "bowel ischemia" or "acute abdominal conditions". DLCT consists of a top layer sensitive to lower-energy photons and a bottom layer sensitive to higher-energy photons. This configuration enables simultaneous acquisition of two energy spectra from a single X-ray beam ensuring consistent spatial alignment and temporal resolution. Spectral raw images allow image post-processing to improve image quality, reduce radiation doses and contrast media doses, and generate multiple quantitative parameters. It has broad potential for early detection, accurate staging, efficacy assessment, and prognosis prediction of liver, pancreatic, and gastrointestinal diseases, as well as for the assessment of digestive system vasculature. DLCT not only provides valuable information for the clinical diagnosis and therapeutic effect evaluation of digestive system diseases but also may play a more important role in the overall management of digestive diseases and in the decision-making of individualized medicine. Question What are the advantages of DLCT compared to traditional single-energy CT in the early detection, staging, and therapeutic evaluation of digestive system diseases? Findings DLCT enhances image quality, improves tissue characterization, and allows for multi-parametric analysis, making it superior in detecting and evaluating liver, pancreatic, and gastrointestinal diseases. Clinical relevance DLCT provides high-quality, multi-parametric imaging that improves the accuracy of diagnosing digestive diseases, facilitates more precise treatment planning, and enhances monitoring of treatment response, ultimately contributing to better patient management and prognosis.

Atomic-Scale Interface Modification in Complex Oxide Heterojunctions for Near-Infrared Photodetection.

Photodetectors that detect near-infrared (NIR) light serve as important components in contemporary energy-efficient optoelectronic devices. However, detecting the low-energy photons of the NIR light has long been challenging since the ease of photoexcitation inevitably involves increasing the background current in the dark. Herein, we report the atomic-scale interface modification in SrRuO3/LaAlO3/Nb-doped SrTiO3 (SRO/LAO/Nb:STO) heterostructures for NIR photodetection. The interfacial band alignment by a polar monolayer LAO allows precise tuning of the Schottky barrier to achieve a specific energy band profile suitable for the NIR photodetection. The SRO/LAO/Nb:STO heterojunctions show a high photoresponsivity up to ∼1.1 mA/W under NIR light irradiation (λ = 850 nm), while keeping the pA-scale dark current. The increase in the responsivity by interface modification is evaluated at a maximum of 1371%. Based on the enhanced NIR photoresponsivity, as a proof of concept, we demonstrate the spatial imaging of NIR signals using a conceptual array of SRO/LAO/Nb:STO heterojunctions. In addition, the experimental-data-based simulation verifies that the array device can implement pulse-number-dependent plasticity, which is based on the characteristic persistent photoconductivity. This study suggests that atomic-scale interface modification is a facile and powerful method for optimizing the photoresponsive properties of complex-oxide-based heterojunctions.

Gamma-ray burst prompt emission from the synchrotron radiation of relativistic electrons in a rapidly decaying magnetic field

Synchrotron radiation from accelerated electrons above the photosphere of a relativistic ejecta is a natural candidate for the dominant radiative process for the prompt gamma-ray burst emission. There is, however, a tension between the predicted low-energy spectral index, $ in the fast cooling regime and observations. Radiating electrons have time to travel away from their acceleration site and may experience an evolving magnetic field. We study the impact of a decaying field on the synchrotron spectrum. We computed the radiation from electrons in a decaying magnetic field, including adiabatic cooling, synchrotron radiation, inverse Compton scatterings, and pair production. We explored the physical conditions in the co-moving frame of the emission region and focused on the fast cooling regime where the radiative timescale of electrons with a Lorentz factor $ m $ responsible for the peak of the emission, $t_ syn m )$, is much shorter than the dynamical timescale $t_ dyn We find that the effect of the magnetic field decay depends on its characteristic timescale $t_ B $: (i) for a slow decay with $t_ B 10\, t_ syn m )$, the effect is very weak and the spectral shape is mostly determined by the impact of the inverse Compton scatterings on the electron cooling, leading to $-3/2 -1$, and (ii) for a fast decay with $0.1 \,t_ syn m t_ B 10 \,t_ syn m )$, the magnetic field decay has a strong impact, leading naturally to the synchrotron marginally fast cooling regime, where alpha tends to $-2/3$, while the radiative efficiency remains high. The high-energy inverse Compton component is enhanced in this regime. (iii) For an even faster decay, the whole electron population is in the slow cooling regime. We conclude that efficient synchrotron radiation in a rapidly decaying magnetic field can reproduce low-energy photon indices ranging from $ to $-2/3$, which is in agreement with the measured value in the majority of gamma-ray burst spectra.

Effect of lead oxide addition on gamma radiation shielding properties of newly developed geopolymers: theoretical and simulation studies

The efficiency of geopolymers as an effective immobilization system for various hazardous waste materials can be enhanced by adding PbO to improve its radiation shielding characteristics. In this study, the impact of PbO addition on the shielding properties of geopolymer composites was examined to evaluate the gamma radiation shielding characteristics of the geopolymer using FLUKA and XCOM computer programs. The results showed that adding 10% and 20% lead oxide significantly improved the shielding properties of the investigated geopolymer, mostly at lower photon energies. The higher values of MAC of 59.66728 cm2/g at 0.015 MeV, and 0.03916 cm2/g at 15 MeV for the investigated geopolymers suggest that these materials have improved radiation shielding at lower and intermediate energies due to higher photoelectric absorption and Compton scattering. The findings of this study provided valuable insights for designing high-performance radiation protection in medical imaging facilities, nuclear power plants, industrial radiography and other special radiation installations. Therefore, GEO doped with 20PbO should be deployed to fortify these facilities against ionizing radiations.

Investigation of electronic and optical properties of InAsSb/GaAs quantum well solar cell (QWSC)

This paper provides a detailed theoretical analysis of a newly developed InAsSb/GaAs quantum well solar cell (QWSC). The study investigates how critical parameters, including the number and thickness of InAsxSb1-x quantum well (QW) layers, the GaAs barrier width, and operating temperature, affect the cell's electrical and optical characteristics. The performance metrics analyzed include current-voltage density (J-V), power-voltage (P-V), and external quantum efficiency (EQE). Results indicate that at 250 K, an optimal configuration of 20 quantum wells, each with a thickness of 4 nm, combined with a 60 nm barrier width, enhances the solar cell's performance significantly. This design achieves a 35.34% increase in short-circuit current and an 82.56% improvement in efficiency compared to a standard p-i-n solar cell. Additionally, the structure extends the absorption band for low-energy photons from 880 nm to 1000 nm. These findings underscore the potential of the proposed QWSC design in advancing photovoltaic technologies by improving efficiency and expanding spectral absorption capabilities, making it a promising candidate for next-generation solar cell applications.

An experimental and computational evaluation of a novel Timepix3 detector for Compton imaging in nuclear medicine

In this paper, we investigate the use of a MiniPIX (Timepix3) hybrid pixel detector as a single layer Compton camera for low-energy (< 200 keV) photons for Nuclear Medicine imaging applications. Literature to date has focused on using Compton camera imaging for high energy photons emitted from non-clinically relevant radionuclides. This paper aims to investigate Compton imaging for nuclear medicine specific radionuclides such as Tc99m (140 keV). For this, a Timepix3 chip with a 1 mm CdTe sensor has been fully characterised in terms of efficiency, energy and timing resolution using a range of point sources, and a detailed model of the detector developed using the EGSnrc Monte Carlo toolkit. Knowledge of the specific interaction points within the detector in the simulation allowed a prediction to be made of the performance of the detector as a Compton camera. Comparison with experimental measurements showed good agreement with simulations, providing validation of the methods employed for image reconstruction. Simple Back Projection (SBP), Filtered Back Projection (FBP) and List Mode-Maximum Likelihood Expectation Maximisation (LM-MLEM) techniques were used for image reconstruction. For all experimental acquisitions, measured Full Width Half Maximum (FWHM) values were within 6% of the modelled values, with Doppler broadening identified as the main limiting factor of the spatial resolution of the system. LM-MLEM consistently returned the highest spatial resolution images, with a 7.3 ± 0.5 mm FWHM achieved for 99mTc point sources, consistent with current clinical gamma cameras. Our results demonstrate the potential of the Timepix3 as a single layer CdTe Compton camera for clinical applications using low energy gamma emitters. The developed MC model will provide a means of investigating larger area, single layer CdTe Compton cameras for nuclear medicine imaging.

Study on Pressure-Induced Band Gap Modulation and Physical Properties of Direct Band Gap Ca3NX3 (X = Cl, Br) for Optoelectronic and Thermoelectric Applications

Utilizing density functional theory, we have comprehensively analyzed the structural, electronic, mechanical, transport, and thermodynamic properties of Ca3NCl3 and Ca3NBr3 photovoltaic materials. Furthermore, we investigated the impact of pressures ranging from 0 to 80 GPa and observed that the applied pressure decreases the atomic distances, resulting in significant changes in the physical properties of both materials. We employed GGA-PBE and TB-mBJ functionals to calculate the band structures and density of states, confirming their semiconducting nature. At 0 GPa, both compounds initially display a direct bandgap (Γ-Γ) of 1.5 eV for Ca3NCl3 and 1.26 eV for Ca3NBr3 based on GGA-PBE calculations. In contrast, the TB-mBJ calculations show an increase in the bandgap to 2.25 eV for Ca3NCl3 and 1.84 eV for Ca3NBr3, respectively. When a pressure of 80 GPa was applied, the direct bandgap of Ca3NCl3 and Ca3NBr3 decreased to 0.23 eV and 0.12 eV with GGA-PBE, and to 0.92 eV and 0.74 eV with TB-mBJ, respectively. It was also observed that the effective mass decreases under applied pressure, making these materials promising candidates for solar cell applications. The mechanical stability of both perovskites was maintained up to 80 GPa. Poisson's ratio and Pugh's ratio indicate that both compounds are brittle at 0 GPa but tend to become more ductile under applied stress. The optical properties reveal that pressure alters the dielectric function, absorption spectra, and optical conductivity, causing a red shift from higher to lower photon energies. Several thermodynamic properties, including heat capacity, Debye temperature, thermal expansion coefficient, and entropy, have been calculated, with their dependencies on temperature and pressure illustrated. Finally, the thermoelectric response of these materials is evaluated by examining how various transport parameters - such as the Seebeck coefficient, electrical and thermal conductivity, and power factor - depend on the temperature.

Design and performance analysis of novel perovskite/CZTSe hybrid solar cell for high efficiency

With newer developments, the solar cells in the market need to be more efficient, affordable, stable, and environment friendly. The perovskite solar cells have already shown very impressive progress in performance since their inception. It has already reached 26 % efficiency and is expected to reach more, owing to its stupendous photovoltaic nature. On the other hand, even with a very high absorption coefficient, the CZTSe solar cell has not crossed the 15 % efficiency mark. Looking at the characteristics of both the materials and considerable differences in band gap, a novel hybrid structure, HTL/Perovskite/CZTSe/CdS/ZnO, has been proposed in this work to implement Perovskite (CH3NH3Pb3−xClx) and CZTSe layer to absorb higher energy and lower energy photons respectively. In this context, choosing a proper Perovskite material becomes more crucial to have the required band alignment for the easy transportation of the excitons. The performance of the cell has been observed in varying parameters like thickness, doping, defects, and temperature. A high efficiency of 30.9 % is achieved which is much higher than the contemporary solar cells. Several other output parameters like Short Circuit Current Density (JSC), Open Circuit Voltage (VOC), Fill-Factor (FF%) characteristics have also been discussed.

Enhancing targeted doses: Low-energy photon lipiodol-enhanced radiotherapy (LEPERT) for liver cancer patients.

This study proposes a novel approach, "Low-energy photon Lipiodol-Enhanced Radiotherapy" (LEPERT), for patients with liver cancer. Moreover, we evaluate the dose difference of the conventional treatment planning with 10 MV X-ray beam (MV-plan) and LEPERT. The computed tomography (CT) was modeled with the Monte Carlo simulation. For LEPERT, 120 kV X-ray beams collimated with CT were irradiated on a virtual tumor filled with Lipiodol at 10-50 mg/mL, which was inserted into a whole-body phantom. A prescribed dose of 40 Gy/4fr was irradiated to achieve D95% of the target. The doses to the target and organs at risk (OARs), such as the bone, normal liver, spinal cord, and kidneys, were evaluated by comparison with conventional radiotherapy with a 10 MV VMAT plan (MV-plan). Differences in the effective energy and off-axis ratio between the measurements and simulations were within 2 keV and 3%, respectively. The D2% of tumors exceeded 130% of the prescribed dose at 50 mg. The difference in the D98% of the tumor between LEPERT and MV-plan was within 0.7 Gy. The V5Gy of the normal liver (>40 mg/mL) was lower for LEPERT than for MV-plan. The V20Gy of the normal liver (>10 mg/mL) for LEPERT was over 80% lower than that for MV-plan. Dose constraints for the OARs were satisfied. The LEPERT can selectively enhanced only the tumor region with sparing the OAR dose. It could be a novel and effective treatment technique in the point that the treatment machine is a general CT device.

Investigation of Gamma Ray Shielding Characteristics of Binary Composites Containing Polyester Resin and Lead Oxide.

Ionizing radiation plays an essential role across various fields but also poses significant health risks, requiring effective shielding solutions. This study focuses on the photon shielding properties of PbO-reinforced composites, specifically PbO-0, PbO-2, PbO-4, PbO-6, PbO-8, and PbO-10, through experimental measurements of photon energies ranging from 59.5 keV to 1408.0 keV. The measurements were taken using an HPGe detector. Experimental results were compared to theoretical calculations. Among the tested composites, PbO-10, which contains the highest concentration of lead oxide (PbO), provided the most effective radiation shielding. This sample demonstrated superior mass and linear attenuation coefficients, offering excellent protection at low photon energies. Furthermore, PbO-10 exhibited the lowest half-value layer (HVL) and tenth-value layer (TVL) values, indicating its efficiency in reducing radiation intensity with thinner material layers. It was determined that the experimental TVL results for PbO-O, PbO-2, PbO-4, PbO-6, PbO-8, and PbO-10 at 59.5 keV photon energy were 9.95, 5.98, 4.77, 3.67, 3.22, and 2.71 cm, respectively. With these outstanding attenuation capabilities, PbO-10 is deemed highly suitable for use in medical, industrial, and radiation-heavy environments. In summary, this research emphasizes the effectiveness of PbO-reinforced composites in gamma-ray shielding, with PbO-10 emerging as the top performer, demonstrating great potential for applications that require durable and efficient radiation protection.

Development of Europium-Doped Barium Fluorochloride Translucent Ceramic Scintillators

In solid-state ionizing radiation detectors, there are two main types of approaches: direct conversion and indirect conversion. The former generally uses semiconductor detectors (e.g., Si photodiodes) that convert radiation directly into electronic signals. The latter, on the other hand, uses phosphors and converts radiation into low-energy photons, which are then detected with a photodetector. Such phosphors are divided into scintillators and storage phosphors. Scintillators emit photons when electrons and holes generated by ionizing radiation recombine at emission centers. These are widely used in security, medical imaging, and basic physics. In storage phosphors, electrons and holes generated by ionizing radiation are temporarily captured in the trapping levels. When the storage phosphors are externally stimulated, these captured electrons and holes are re-excited and recombine at emission centers. Storage phosphors are used as personal dosimeters and imaging plates.In general, the requirements for scintillators are high light yield (LY), short decay time constants, large effective atomic number (Z eff), low afterglow levels, and chemical stability. The search for scintillators has a long history, but no material has been developed that fulfills all the required properties. Therefore, various scintillators with different chemical compositions have been developed, and scintillators have been selected and used for different measurement applications.Single crystals have been the most commonly used scintillator material form because of their high light transfer efficiency at emission wavelengths. However, these are problematic because of the long time and high cost required for their preparation. To solve the problems that single crystals have, translucent ceramics have attracted attention in recent years. Ceramics are synthesized by solid-phase reactions, which generally take a shorter time and cost less than single crystals grown by melt growth techniques. In this context, our group has successfully developed translucent ceramic scintillators with high luminescence efficiency. We reported that Y3Al5O12:Ce [1] and Lu3Al5O12:Ce [2] translucent ceramics showed higher LYs than single crystals of the same composition. Since translucent ceramics have only recently begun to be developed, only a few materials have been fabricated.In this study, we developed BaFCl:Eu in translucent ceramic form. Ba-based complex anions have been actively studied as scintillators and dosimetric materials because of their high luminescence intensity and high Z eff (~50). In particular, BaFCl:Eu is known to have an emission wavelength suitable for general photodetectors (~380 nm), a relatively fast decay time constant (~5 μs), and chemical stability [3]. These properties are suitable for scintillators to detect X- and γ-rays. BaFCl:Eu has been fabricated in opaque ceramics and studied in detail with dosimetric properties, but there are still no reports of BaFCl:Eu translucent ceramics. In this study, BaFCl translucent ceramics doped with 0.01, 0.1, 0.5, and 1.0% Eu were synthesized by the spark plasma sintering method. The optical and scintillation properties of the fabricated samples were investigated, and their potential as scintillators was examined.Photoluminescence (PL) emission spectra and X-ray-induced scintillation spectra of the BaFCl:Eu translucent ceramics were measured, both of which were dominated by an emission peak at 390 nm. According to the report [3], this emission peak was suggested to originate from the 5d–4f transition of Eu2+. Pulse height spectra were measured to determine a scintillation light yield, which was 15,000 ph/MeV at a maximum. This value is about twice that of commercially used Gd2SiO5:Ce (8,000 ph/MeV, [4]).We will present a detailed attribution of the luminescence in BaFCl:Eu translucent ceramics and the concentration dependence of the samples.<reference>[1] T. Yanagida et al., IEEE Trans. Nucl. Sci., 52, 1836 (2005).[2] T. Yanagida et al., Radiat. Meas., 46, 1503 (2011).[3] M. Ignatovych et al., Radiat. Prot. Dosimetry, 84, 185 (1999).[4] I. G. Valais et al., IEEE Trans. Nucl. Sci., 54, 11 (2007).

Fabrication of (K,Rb)2CuCl3 and (K,Rb)2CuBr3 Single Crystal Scintillators with Efficient Luminescence

Scintillators are phosphor materials that emit many low-energy photons upon exposure of high-energy ionizing radiation such as X- and γ-rays. They have been utilized in combination with photodetectors for radiation measurements, including medical imaging [1], underground resources exploration [2], luggage inspection [3], and structural analysis of materials [4]. The required characteristics of scintillators are different depending on the applications. For example, high light yield (LY) for high energy resolution and high signal-noise ratio, short decay time for high time resolution, large effective atomic number for high interaction probability with ionizing radiation, and low hygroscopicity for long-term usability are important. Halide crystals such as Tl-doped CsI and NaI have been utilized as practical scintillators because of their high LY owing to the medium bandgap energy (5.8–6.3 eV) [4, 5]. However, most halide crystals have issues related to chemical instability due to hygroscopicity. Thus, novel non-hygroscopic scintillators with high LY have been desired. Nowadays, Cu-based halide scintillators have received attention owing to good properties such as high photoluminescence quantum yield (PLQY), scintillation LY, and no hygroscopicity. We have focused on the alkali copper halide group such as A 2CuX 3 (A = K, Rb X = Cl, Br). They showed high PLQY (~100%) attributed to the recombination of self-trapped excitons under UV and X-ray irradiations [6, 7]. However, their scintillation LYs under γ-rays have not been clarified. According to Hume-Rothery rules [8], a continuous solid solution containing two or more components can be easily formed when two substances with similar ionic radius and crystal structure are partially mixed in the matrix. In continuous solid solutions, emission properties of phosphors were improved by optimizing energy levels in the bandgap and lattice defects involved in the luminescence [9]. On the basis of the rules, the continuous solid solutions of (K,Rb)2CuCl3 and (K,Rb)2CuBr3 can be grown. Thus, we fabricated (K,Rb)2CuCl3 and (K,Rb)2CuBr3 to enhance the scintillation properties. In this presentation, the scintillation properties such as the X-ray-induced scintillation spectra, the scintillation decay curves, afterglow curves, and pulse-height spectra of 1 37Cs γ-rays (662 keV) measurements will be presented.[1] C.W. Eijk., Phys. Med. Biol., 47 (2002) R85. [2] A. Nikitin et.al., IEEE Nucl. Sci. Symp. Med. Imag. Conf. (2010) 1214. [3] V.D. Ryzhikov et.al., IEEE Symposium Conference Record Nuclear Science (2004) 4291. [4] V.V. Nagarkar et.al., IEEE Trans. Nucl. Sci. 45 (1998) 492. [5] M. Moszynski et.al., Nucl. Instrum. Methods Phys. Res. A (2004) 4291. [6] T.D Creason et.al., Chem. Mater. 32 (2020).