Incoming Photon Research Articles

High Quantum Yields and Biomedical Fluorescent Imaging Applications of Photosensitized Trivalent Lanthanide Ion-Based Nanoparticles.

In recent years, significant advances in enhancing the quantum yield (QY) of trivalent lanthanide (Ln3+) ion-based nanoparticles have been achieved through photosensitization, using host matrices or capping organic ligands as photosensitizers to absorb incoming photons and transfer energy to the Ln3+ ions. The Ln3+ ion-based nanoparticles possess several excellent fluorescent properties, such as nearly constant transition energies, atomic-like sharp transitions, long emission lifetimes, large Stokes shifts, high photostability, and resistance to photobleaching; these properties make them more promising candidates as next-generation fluorescence probes in the visible region, compared with other traditional materials such as organic dyes and quantum dots. However, their QYs are generally low and thus need to be improved to facilitate and extend their applications. Considerable efforts have been made to improve the QYs of Ln3+ ion-based nanoparticles through photosensitization. These efforts include the doping of Ln3+ ions into host matrices or capping the nanoparticles with organic ligands. Among the Ln3+ ion-based nanoparticles investigated in previous studies, this review focuses on those containing Eu3+, Tb3+, and Dy3+ ions with red, green, and yellow emission colors, respectively. The emission intensities of Eu3+ and Tb3+ ions are stronger than those of other Ln3+ ions; therefore, the majority of the reported studies focused on Eu3+ and Tb3+ ion-based nanoparticles. This review discusses the principles of photosensitization, several examples of photosensitized Ln3+ ion-based nanoparticles, and in vitro and in vivo biomedical fluorescent imaging (FI) applications. This information provides valuable insight into the development of Ln3+ ion-based nanoparticles with high QYs through photosensitization, with future potential applications in biomedical FI.

High-temperature transport properties of a two-dimensional weakly doped parabolic semiconductor

A version of the Mexican-hat Hamiltonian is used to study high-temperature transport properties of a two-dimensional weakly doped semiconductor with electron-hole symmetric bands. For a finite doping level and a temperature-dependent band gap, we find a closed analytical form of the temperature-dependent chemical potential. The effective concentrations of charge carriers participating in transport coefficients are analyzed in the space spanned by the total electron concentration and temperature. It is shown that these concentrations are the sum of a residual contribution and two thermally activated contributions, with a complicated dependence on temperature. The analytical expression for the Hall coefficient RHis also found. It is argued that it is a non-monotonic function of the doping level with the maximum at the doping nmax that is a linear function of temperature at high enough temperatures. The analysis of the real part of the interband conductivity shows that it is inversely proportional to incoming photon energy at low temperatures and that it is nearly constant over a wide energy range at high temperatures. This results are expected to be of significant importance in understanding transport and optical properties of weakly doped two-dimensional semiconductors with nearly symmetric parabolic bands.&#xD.

Telescope imaging beyond the Rayleigh limit in extremely low SNR

Abstract The Rayleigh limit and low Signal-to-Noise Ratio (SNR) scenarios pose significant limitations to optical imaging systems used in remote sensing, infrared thermal imaging, and space domain awareness. In this study, we introduce a Stochastic Sub-Rayleigh Imaging (SSRI) algorithm to localize point objects and estimate their positions, brightnesses, and number in low SNR conditions, even below the Rayleigh limit. Our algorithm adopts a maximum likelihood approach and exploits the Poisson distribution of incoming photons to overcome the Rayleigh limit in low SNR conditions. In our experimental validation, which closely mirrors practical scenarios, we focus on conditions with closely spaced sources within the sub-Rayleigh limit (0.49-1.00R) and weak signals (SNR less than 1.2). We use the Jaccard index and Jaccard efficiency as a figure of merit to quantify imaging performance in the sub-Rayleigh region. Our approach consistently outperforms established algorithms such as Richardson-Lucy and CLEAN by 4X in the low SNR, sub-Rayleigh regime. Our SSRI algorithm allows existing telescope-based optical/infrared imaging systems to overcome the extreme limit of sub-Rayleigh, low SNR source distributions, potentially impacting a wide range of fields, including passive thermal imaging, remote sensing, and space domain awareness.

Study of promising lithium-based lead-free double perovskites Li2AuBiX6 (X = Cl, Br, and I) for optoelectronic and other renewable energy applications

The current study effort primarily focuses on the computational investigation of the physical properties of Li2AuBiX6 (X = Cl, Br, and I) double perovskites (DPs) utilizing the Density Functional Theory (DFT) framework. The structural and elastic characteristics have been evaluated to reveal phase and mechanical stability. The assessed formation energy and elasticity constants calculations validate that the examined DPs possess cubic phase, exhibit stability, and demonstrate ductility. The band structure analysis has been accomplished with a modified Becke-Johnson (mBJ) potential. Theband structure simulations reveal that Li2AuBiCl6, Li2AuBiBr6, and Li2AuBiI6 possess an indirect energy gap, with values of 1.12 eV, 0.77 eV, and 0.084 eV, respectively. We further examined the optical parameters in the spectrum of incoming photons from 0 to 4 eV. Considerable absorbance in the visible spectrum has been observed for Li2AuBiX6 (X = Cl, Br, and I), suggesting that these DPs are compatible with photovoltaics. Finally, we have computed thermoelectric (TE) characteristics in relation to temperatures within the range of 100 to 600 K. The investigated DPs might be suitable for thermoelectric systems, as indicated by the moderate values of the figure of merit, which needs to be improved. The obtained absorption and figure of merit values surpass similar perovskites Rb2AuBiX6. Hence, the current work might be advantageous for developing novel photovoltaic and TE systems.

The Large Imaging Spectrometer for Solar Accelerated Nuclei (LISSAN): A next-generation solar gamma-ray spectroscopic imaging instrument concept

We present the Large Imaging Spectrometer for Solar Accelerated Nuclei (LISSAN), a new solar dedicated satellite instrument concept. LISSAN relies on an indirect Fourier imaging technique valid over an energy range from 40 keV up to 100 MeV. Spatial information is encoded into 15 moiré patterns by 15 pairs of slightly offset grids (bigrids) separated by a fixed distance enabling a predicted spatial resolution of 10”. The time, location, and energy of each incoming photon is recorded via a pixelated gadolinium aluminium gallium garnet (GAGG) crystal scintillator detector placed in alignment with each bigrid, therefore providing simultaneous imaging and spectroscopy from the same imaging system. X-ray and gamma-ray emission are key diagnostics of electron and ion acceleration, respectively. However, despite being a fundamental process that occurs throughout the Universe, particularly in the solar atmosphere, only one resolved gamma-ray image of ion acceleration in a solar flare has ever been achieved. LISSAN will shed new light on this process by providing spectral resolution better than 1.5% FWHM at 6.1 MeV, an imaging effective area at 2.2 MeV of 100 cm2 (more than 25 times greater than past missions such as RHESSI) and a 10 s cadence. Thanks to these significant advances over the previous satellite-based solar detectors, LISSAN will provide reliable imaging and the spectral characterization of both electron and ion acceleration in solar eruptive events simultaneously for the first time, enabling to it to answer several important open questions regarding solar particle acceleration and the initiation of space weather events.

The role of outflows in black-hole X-ray binaries

The hot inner flow in black-hole X-ray binaries is not just a static corona rotating around the black hole: it must be partially outflowing. It is therefore a mildly relativistic ``outflowing corona.'' We have developed a model in which Comptonization takes place in this outflowing corona. In all of our previous work, we assumed a rather high outflow speed of $0.8c$. Here, we investigate whether an outflow with a significantly lower speed can also reproduce the observations. Thus, in this work we consider an outflow speed of $0.1c$ or less. As in all of our previous work, we used a Monte Carlo code to compute not only the emergent X-ray spectra, but also the time lags that are introduced to the higher-energy photons with respect to the lower-energy ones via multiple scatterings. We also record the angle (with respect to the symmetry axis of the outflow) and the height at which photons escape. Our results are very similar to those of our previous work, with some small quantitative differences that can be easily explained. We are again able to quantitatively reproduce five observed correlations: (a) the time lag as a function of Fourier frequency, (b) the time lag as a function of photon energy, (c) the time lag as a function of Gamma , (d) the time lag as a function of the cutoff energy in the spectrum, and (e) the long-standing radio--X-ray correlation -- and all of them with only two parameters, which vary in the same ranges for all the correlations. Our model does not require a compact, narrow relativistic jet, although its presence does not affect the results. The essential ingredient of our model is the parabolic shape of the Comptonizing corona. The outflow speed plays a minor role. Furthermore, the bottom of the outflow, in the hard state, looks like a ``slab'' to the incoming soft photons from the disk, and this can explain the observed X-ray polarization, which is along the outflow. In the hard-intermediate state, we predict that the polarization of GX 339-4 will be perpendicular to the outflow.

XMM-Newton and NuSTAR discovery of a likely IP candidate XMMU J173029.8--330920 in the Galactic disc

We aim to characterise the population of low-luminosity X-ray sources in the Galactic plane by studying their X-ray spectra and periodic signals in the light curves. We are performing an X-ray survey of the Galactic disc using and the source XMMU J173029.8--330920 was serendipitously discovered in our campaign. We performed a follow-up observation of the source using our pre-approved target of opportunity time. We used various phenomenological models in xspec for the X-ray spectral modelling. We also computed the Lomb-Scargle periodogram to search for X-ray periodicity. A Monte Carlo method was used to simulate 1000 artificial light curves in order to estimate the significance of the detected period. We also searched for X-ray, optical, and infrared counterparts of the source in various catalogues. The spectral modelling indicates the presence of an intervening cloud with $N_ H $ that partially absorbs the incoming X-ray photons. The X-ray spectra are best fit by a model representing emission from a collisionally ionised diffuse gas with a plasma temperature of $kT=26^ $ keV. Furthermore, an Fe $K_ alpha $ line at $6.47^ $ keV was detected with an equivalent width of the line of $312 eV. We discovered a coherent pulsation with a period of $521.7 s. The 3--10 keV pulsed fraction of the source is around sim 50--60<!PCT!>. The hard X-ray emission with plasma temperature $kT=26^ $ keV, iron $K_ alpha $ emission at 6.4 keV, and a periodic behaviour of $521.7 s suggest XMMU J173029.8--33092 to be an intermediate polar. We estimated the mass of the central white dwarf to be $0.94-1.4\ odot $ by assuming a distance to the source of $ kpc.

Interpolation insights: Accurate mass attenuation coefficient and effective atomic number estimation in PbO and BaO doped borosilicate glasses

Interpolation techniques such as Piecewise Cubic Hermite Interpolating Polynomials (PCHIP) and Cubic Splines (CS) were used to estimate the mass attenuation coefficient values (MAC) and the effective atomic number values (Zeff) of borosilicate glasses doped with PbO and BaO. The mathematical models were used to obtain a function between the parameters and the energy of the incoming photons, to provide a better understanding of the glass system. The glasses had a composition of 10Na2O–15PbO-(65-x)B2O3–10SiO2-xBaO, where x = 5, 10, 15, 20, and 25 mol%. The derived values were compared against theoretical data obtained from Phy-X, to determine the accuracy of the mathematical models. The results demonstrate that both the CS and PCHIP methods are useful tools that can accurately be used to determine the MAC and Zeff values of the investigated samples. For instance, at certain energies such as 0.103 MeV, the relative difference between the MAC values obtained through PCHIP and through Phy-X is as low as 0.07, demonstrating the effectiveness of the PCHIP model at these energies. The same is true for the Zeff values, where the same relative difference at 0.384 MeV is as low as 0.0002. Therefore, both the mathematical models demonstrate an effective ability at interpolating the MAC and Zeff values of the investigated glass system.

SrO–ZnO–PbO–B2O3 glassy insights: Unveiling the structural and optical features for gamma ray shielding efficacy

The melt-quenching approach was utilised to synthesize amorphous SrO–ZnO–PbO–B2O3 glasses, with FTIR spectroscopy applied to the samples to reveal the various bonds' stretching and bending vibrations. With PbO introduced to the network, the UV–Vis absorption spectrum's absorption peak shifts towards the higher wavelength values, while Tauc plot analysis of the UV–Vis spectra reveals a 2.957–2.569 eV decrease in the band gap energy. The radiation shielding properties are examined via Phy-X program. The mass attenuation coefficient (MAC) has an inverse relation with the energy, which demonstrated the greater penetration ability of radiation that contains higher energy. In terms of the MAC values at low energies the results revealed a greater difference, while they are almost identical at higher energies. The linear attenuation coefficient (LAC) was evaluated and the chemical composition's influence discussed, with the LAC values in the order of SZPB1 <SZPB2 <SZPB3 <SZPB4. This confirms that the PbO addition leads to increased LAC values. The half value layer (HVL) decreases with increased concentration of PbO. This suggests that the higher the glass system's PbO content, the thinner the glass system needs to be to attenuate half of the incoming photons.

Predictive modeling of novel GaAgX2 (X = S, Se) chalcogenides: First-principles study of electronic, optical, and thermoelectric properties

The most prominent aspects of ternary-type chalcogenides are their tunable optical abilities and outstanding thermoelectric stability. Here the advanced density functional theory is used to examine the complicated interaction of the electronic structure, optical, thermodynamic, and thermoelectric properties of novel GaAgX2 (X = S, Se) chalcogenides. The total energies vs volume of the two materials were computed to formulate ground state characteristics. Both the materials confirmed to have direct band gap nature with an energy gap of 0.8 eV, and 2.2 eV, using TB-mBJ potential, respectively. As compared to GaAgS2, the crystal structure of GaAgSe2 have more covalent bonds that enlarged the covalency and results in wider energy gap of GaAgSe2 as compared to GaAgS2. For the negative value of ε1(ω), these materials display metallic nature, resulting to show a total reflection of the incoming photons. The GaAgS2 displays better absorption than GaAgSe2 materials with higher energy photons. With a few high peaks of refractive index in (2.8–5.5) eV energy range, suggesting these materials appropriate to be used in optical devices. These materials have positive Seebeck coefficients and are confirmed to have a p-type nature. At ambient temperature, GaAgS2 has lower thermal conductivity than GaAgSe2.

DFT aided comparative screening of mechanical, optoelectronic, and transport properties of double perovskites Cs2ScAuX6 (X = Cl, Br, and I) for green energy applications

A comprehensive comparative analysis has been performed to investigate the Cs2ScAuX6 (X = Cl, Br, and I) employing density functional theory. The WIEN2k code has been applied to optimize the structural arrangement of perovskites and calculate various aspects such as mechanical, optoelectronic, and transport characteristics. The results demonstrated that these perovskite compounds had both structural and chemical stability. The analyzed elastic characteristics of the Cs2ScAuX6 have shown that these compounds are mechanically stable, have anisotropy toughness, and provide durability against plastic deformation. The electronic characteristics are determined precisely and accurately using the Trans-Blaha-modified Becke-Johnson (TB-mBJ) potential. The compounds Cs2ScAuCl6, Cs2ScAuBr6, and Cs2ScAuI6 are semiconductors and have band gaps of 1.6, 1.5, and 1.05 eV, respectively, demonstrating an indirect nature. An investigation examines the optical characteristics within the energy range of 0–6 eV. The chosen materials reveal transparency in the lower energy spectrum of incoming photons and exhibit significant absorption and transmission of light. Therefore, it can be inferred that Cs2ScAuX6 materials possess optical properties that make them suitable for utilization in photovoltaic devices. Further, these materials elaborate substantial electrical conductivity, power factors, and figures of merit (ZT), making them efficient thermoelectric resources. At last, these results would be advantageous for experimental researchers and have also unveiled the substantial capability of these substances to be utilized in solar energy harvesting and thermoelectric devices.

X-ray radiation shielding: Enhanced performance with BaCO3 nanocrystal-infused composite polyester/PVA/BaCO3 exhibiting medicine capsule-like structure

The advanced technology for effective X-ray radiation shielding is increasingly important. The use of new materials and innovative strategies has the potential to revolutionize radiation shielding, making it safer due to its outstanding characteristics. Herein, the effect of using nanocrystals of BaCO3 in a composite polyester/PVA/BaCO3 with medicine capsule-like structure are reported. Our findings showed that the BCO60 composite had an excellent shielding characteristic, it was able to attenuate half of the incoming photon energy for only 0.028 cm form their thickness. We compared our experimental findings to theoretical values through the Phy-X/PSD online software and show a very good match. The medicine capsule-like environmentally inspired X-ray radiation shield provides new strategies for design and preparation X-ray radiation shielding in the future.

Spectral Photon-Counting Computed Tomography: Technical Principles and Applications in the Assessment of Cardiovascular Diseases.

Spectral Photon-Counting Computed Tomography (SPCCT) represents a groundbreaking advancement in X-ray imaging technology. The core innovation of SPCCT lies in its photon-counting detectors, which can count the exact number of incoming x-ray photons and individually measure their energy. The first part of this review summarizes the key elements of SPCCT technology, such as energy binning, energy weighting, and material decomposition. Its energy-discriminating ability represents the key to the increase in the contrast between different tissues, the elimination of the electronic noise, and the correction of beam-hardening artifacts. Material decomposition provides valuable insights into specific elements' composition, concentration, and distribution. The capability of SPCCT to operate in three or more energy regimes allows for the differentiation of several contrast agents, facilitating quantitative assessments of elements with specific energy thresholds within the diagnostic energy range. The second part of this review provides a brief overview of the applications of SPCCT in the assessment of various cardiovascular disease processes. SPCCT can support the study of myocardial blood perfusion and enable enhanced tissue characterization and the identification of contrast agents, in a manner that was previously unattainable.

A comprehensive DFT insight on physical features regarding potential applicability of double perovskites K2YCuZ6 (Z = Cl, Br) for energy harvesting applications

Herein, a comprehensive investigation of the structural, mechanical, optoelectronic, and thermoelectric features of K2YCuZ6 (Z = Cl, Br) is presented concerning their potential utilization inphotovoltaic and thermoelectric devices. The observation of formation energy and fitting of the Murnaghan equation of state ensured thermodynamic and structural stability, respectively. The mechanical stability of K2YCuCl6 and K2YCuBr6 is determined by employing Born Huang stability criteria based on their elastic constants. The analysis of elastic parameters further classified these materials as anisotropic as well as ductile. The band gaps of K2YCuCl6 and K2YCuBr6 have been computed using the TB-mBJ potential, resulting in values of 2.4 and 1.56 eV, respectively. An extensive analysis of the optical characteristics of these compounds is carried out in the energy region spanning from 0 to 8 eV. These compounds are discovered to have substantial absorbance and conductive properties in the visible and ultraviolet energy ranges. On the other hand, they exhibit transparency to incoming photons with lower energy levels. Our examination of the optical characteristics indicates that these compounds are very suitable for use in photovoltaic applications. The evaluation of thermoelectric parameters resulted in the p-type semiconducting nature and higher figure of merit of 0.78, and 0.80 at 300 K. Therefore, K2YCuZ6 that has not been verified experimentally has great potential for solar cell and thermoelectric applications, indicating its ability to contribute to the progress of alternative energy sources.

A prototype Radiation Energy Measuring Integrated Circuit with an asynchronous current-pulse reset block providing analog-to-digital conversion in 28 nm CMOS

In this paper we introduce a prototype Radiation Energy Measuring Integrated Circuit (REMIC) fabricated in a 28 nm CMOS process. The chip operates in a single-photon counting (SPC) mode and contains 100 pixels with a size of 50 μm × 50 μm. It is designed for precise energy measurements using asynchronous analogue-to-digital conversion. The proposed architecture allows both fast signal processing and precise energy measurement of incoming photons to be performed independently in each pixel, occupying a small pixel area. The integrated circuit (IC) has dimensions of 1.1 mm × 1.1 mm and is currently undergoing preliminary measurements. The paper focuses on the methodology used to mitigate process variations in each of the recording channels.

Optical Flow for Spike Camera with Hierarchical Spatial-Temporal Spike Fusion

As an emerging neuromorphic camera with an asynchronous working mechanism, spike camera shows good potential for high-speed vision tasks. Each pixel in spike camera accumulates photons persistently and fires a spike whenever the accumulation exceeds a threshold. Such high-frequency fine-granularity photon recording facilitates the analysis and recovery of dynamic scenes with high-speed motion. This paper considers the optical flow estimation problem for spike cameras. Due to the Poisson nature of incoming photons, the occurrence of spikes is random and fluctuating, making conventional image matching inefficient. We propose a Hierarchical Spatial-Temporal (HiST) fusion module for spike representation to pursue reliable feature matching and develop a robust optical flow network, dubbed as HiST-SFlow. The HiST extracts features at multiple moments and hierarchically fuses the spatial-temporal information. We also propose an intra-moment filtering module to further extract the feature and suppress the influence of randomness in spikes. A scene loss is proposed to ensure that this hierarchical representation recovers the essential visual information in the scene. Experimental results demonstrate that the proposed method achieves state-of-the-art performance compared with the existing methods. The source codes are available at https://github.com/ruizhao26/HiST-SFlow.

The first cut is the cheapest: optimizing Athena/X-IFU-like TES detectors resolution by filter truncation

The X-ray Integral Field Unit (X-IFU) instrument on the future ESA mission Athena X-ray Observatory is a cryogenic micro-calorimeter array of Transition Edge Sensor (TES) detectors designed to provide spatially-resolved high-resolution spectroscopy. The onboard reconstruction software provides energy, spatial location and arrival time of incoming X-ray photons hitting the detector. A new processing algorithm based on a truncation of the classical optimal filter and called 0-padding, has been recently proposed aiming to reduce the computational cost without compromising energy resolution. Initial tests with simple synthetic data displayed promising results. This study explores the slightly better performance of the 0-padding filter and assess its final application to real data. The goal is to examine the larger sensitivity to instrumental conditions that was previously observed during the analysis of the simulations. This 0-padding technique is thoroughly tested using more realistic simulations and real data acquired from NASA and NIST laboratories employing X-IFU-like TES detectors. Different fitting methods are applied to the data, and a comparative analysis is performed to assess the energy resolution values obtained from these fittings. The 0-padding filter achieves energy resolutions as good as those obtained with standard filters, even with those of larger lengths, across different line complexes and instrumental conditions. This method proves to be useful for energy reconstruction of X-ray photons detected by the TES detectors provided proper corrections for baseline drift and jitter effects are applied. The finding is highly promising especially for onboard processing, offering efficiency in computational resources and facilitating the analysis of sources with higher count rates at high resolution.

A systematic first-principles investigation of the structural, electronic, optical, thermodynamic and transport properties of lead-free pyrochlore oxides Q2Sb2O7 (Q= Be, Ca, Sr) for low-Cost energy applications

A systematic study has been performed on structural, optical and thermophysical properties of newly designed pyrochlore oxides Q2Sb2O7 (Q = Be, Ca, Sr) employing FP-LAPW based first-principles calculations. The GGA approach was used to treat exchange and correlation potentials. The investigated E-V plots reveals that Sr2Sb2O7 is the most stable structure compared to Be2Sb2O7/Ca2Sb2O7. A direct energy bandgap of 0.29 eV is evident from band structure plot of Be2Sb2O7, however, Ca2Sb2O7/Sr2Sb2O7 possess indirect energy bandgaps of magnitude 1.47/1.467 eV. The studied materials show maximum absorption of incoming photons in near UV region as shown in ε2(ω) plots, however, considerable absorption in visible region is also present. Ca2Sb2O7/Sr2Sb2O7 are effective optical material with a n(ω) value between 1.0 and 2.0. Optical properties of pyrochlore oxides reveal that these materials are potential candidates for shielding materials in upper UV region. A photon reflection of up to 60% is evident from the R(ω) in UV region, however, in IR and visible regions, the reflectance is negligible. Based on calculated values of Seebeck coefficient (S), we can state that Be2Sb2O7 is n-type semiconductor whereas Ca2Sb2O7/Sr2Sb2O7 are p-type semiconductors. The most effective thermoelectric material among Q2Sb2O7 (Q = Be, Ca, Sr) is Ca2Sb2O7 as its ZT value is highest (∼1.05) in the entire temperature range. Thermodynamic properties of Q2Sb2O7 (Q = Be, Ca, Sr) are also evaluated to check dynamical stability and appropriateness of these materials in thermal applications. The investigated outcomes show that these pyrochlore oxides are potential candidates for thermoelectric and optoelectronic device applications.

The Hirshfeld topological surfaces, volumes, and their voids charge density interplay on radiation shielding properties: A case study of carbide-based ceramics

Transition metal carbides (TMCs) are explored for their potential as radiation shielding materials, with a focus on their γ-ray attenuation properties. These high-density materials, including WC, TaC, HfC, NbC, and VC, are evaluated across an energy range of 0.015–15.0 MeV. Notably, at low incoming photon energy (0.0150 MeV), these TMCs exhibit mass attenuation coefficients (MAC) (TMC, MAC (g/cm2)): (WC, 130.417), (TaC, 125.730), (HfC, 120.873), (NbC, 23.751), and (VC, 32.377) and effective atomic numbers (Zeff) from 22.69 to 73.68. These values surpass those of silicon dioxide (SiO2), highlighting the superior γ-ray attenuation capabilities of TMCs. TMCs exhibit a distinct trend in MAC values, with tungsten carbide (WC) consistently demonstrating the highest MAC values, making it the most efficient γ-ray attenuator. Hafnium carbide (HfC) closely follows, with tantalum carbide (TaC) exhibiting lower MAC values, while niobium carbide (NbC) and vanadium carbide (VC) display the lowest values. These differences can be attributed to variations in material composition and structure. Furthermore, the study delves into the impact of charge density within Hirshfeld voids on LAC values, revealing that as X⁴⁺ … C interactions increase due to higher charge density, LAC values rise. This fine-tuning of topological and charge density distributions within the crystal's voids offers a promising avenue to optimize these materials for enhanced radiation shielding effectiveness. Overall, this research contributes to the understanding of the potential utility of TMCs in radiation shielding applications, showcasing the interplay between crystal structure, composition, and charge distribution as key factors in determining their radiation attenuation capabilities.

Single-photon counting detectors for diffraction-limited light sources

When first introduced, single-photon counting detectors reshaped crystallography at synchrotrons. Their fast readout speed enabled, for example, shutter-less data collection and fine slicing of the rotation angle and boosted the development of new experimental techniques like ptychography. Under optimal conditions, single-photon counting detectors provide an unlimited dynamic range with image noise only limited by the Poisson statistics of the incoming photons. Counting the pulses from individual photons, essentially what made the detectors so successful, also causes the main drawback, which is the loss of efficiency at high photon fluxes due to pulse pileup in the analog front end. To fully take advantage of diffraction-limited light sources, the next-generation single-photon counters need to improve their count rate capabilities in the same order of magnitude as the increased flux. Moreover, fast frame rates (a few kHz) are required to cope with the shorter dwell time achievable, thanks to the higher flux. Detector architecture with multiple comparators and counters can open new possibilities for energy-resolved imaging, while interpixel communication can overcome the issues arising from charge sharing and reduce the loss of efficiency at the pixel corners. Coupling single-photon counting detectors to high-Z sensors for hard X-ray detection (&gt;20 keV) and to low-gain avalanche diodes (LGADs) for soft X-rays is also necessary to make use of the increased coherence of the new light sources over the full radiation spectrum. In this paper, we present possible strategies to improve the performance of single-photon counting detectors at the fourth-generation synchrotron sources and compare them to charge integrating detectors.