Incoming Photon Energy Research Articles

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.

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.

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.

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.

Designing High-Density of PbO-Enriched Telluro-Borate Glasses for Improved Radiation Shielding: A Comprehensive Study of Attenuation Parameters

Several radiation shielding parameters for (75-x) B2O3−10TeO2−13SrCO3 −2ZnO-xPbO glasses were evaluated between 0.284 and 1.333 MeV. The PbO content in the glass has a positive relationship with the density of the glasses, leading to BTSZP0, the glass with no PbO, having the smallest density, while BTSZP5, which has 40 PbO mol%, has the greatest density. Radiation shielding parameters such as mass attenuation coefficients (MAC) and other related factors were computed, and relationships between PbO content, energy, and density are graphed. Linear attenuation coefficient (LAC) is reported and we evaluated the impact of density on the LAC values. By adding more PbO atoms, the density of the samples increased, leading to a higher LAC. The BTSZP0 sample has the highest HVL at all tested energies, with the BTSZP5 sample having the lowest HVL. Mean free path (MFP) has an inverse relationship with the density of each sample but increases with greater incoming photon energy. The effective atomic number (Zeff)values peak at low photon energies and rise significantly with increasing PbO content. The MFP and TVL of the BTSZP glasses are compared against previously tested glass samples at a set energy, and the values demosntrated the effectiveness of the BTSZP glasses.

Elastic, mechanical, and radiation shielding behaviors of copper-phosphate binary-glasses with diverse copper valence-states: [formula omitted

This paper presents a comprehensive investigation of the mechanical, elastic, and radiation shielding properties of glass systems comprising yCuOx + (100-y)P2O5, where y = 45, 50, and 55 mol%, and x = 1, 2, 3, or 4, representing different copper-valence-states (i.e., R(Cu+)=Cu+/(Cu++Cu++)). Three series of copper-phosphate glasses were synthesized, and their physical properties, including density, molar-volume, oxygen-molar-volume, and packing-density, were analyzed. The elastic-moduli and Poisson's-ratio were calculated using the Makishima-Mackenzie model, showing significant influence by the copper-valence-state. The micro-hardness Hv ∈(17.3–19.0 MPa), E ∈(38.6–45.82 MPa), and Poisson's ratio∈ (0.419–0.426) increased as a function of R (Cu+). Furthermore, the radiation shielding properties of the glass systems were explored employing the XCOM and Phys-X software. Mass-attenuation-coefficients (μm) were found to follow the order μmseries-a <μmseries-b< μmseries-c in the incoming photon energies ranging from 0.015 to 15 MeV. The μm values increased with increasing copper-valence-state and decreased with photon energy. Energy absorption and exposure buildup factors exhibited maximum values around 0.15 MeV, shifting to higher energies with increasing copper-valence-state.

Comparison of Threshold Energy Calibrations of a Photon-Counting Detector and Impact on CT Reconstruction

Photon-counting detectors (PCDs) require a more complicated calibration process than the standard energy-integrating detectors. The first step of a PCD calibration is the threshold energy calibration. This step determines the linear pixel-by-pixel relationship between the output voltage of a PCD and the incoming photon energy. It can be performed in several ways. Three different methods were implemented, requiring only a standard X-ray source, or an X-ray source combined with K-edge materials or a PCD response model. The three resulting calibrations were first evaluated on monoenergetic and projection measurements. The impact of the threshold calibration on computed tomography (CT) images was also studied. The calibration method fitting a detector response model to polyenergetic measurements presented the best spectral accuracy when estimating monoenergetic peaks. This calibration also produced a better pixel homogeneity in an air projection. However, no significant improvement was observed in the noise power spectrum (NPS) and ring artifact evaluation of a conventional CT image for this calibration compared to a calibration providing lower spectral accuracy or lower pixel homogeneity.

Pure spin current injection of single-layer monochalcogenides

We compute the spectrum of pure spin current injection in ferroelectric single-layer SnS, SnSe, GeS, and GeSe. The formalism takes into account the coherent spin dynamics of optically excited conduction states split in energy by spin–orbit coupling. The velocity of the electron’s spins is calculated as a function of incoming photon energy and angle of linearly polarized light within a full electronic band structure scheme using density functional theory. We find peak speeds of 520, 360, 270 and 370 Km s−1 for SnS, SnSe, GeS and GeSe, respectively which are an order of magnitude larger than those found in bulk semiconductors, e.g., GaAs and CdSe. Interestingly, the spin velocity is almost independent of the direction of polarization of light in a range of photon energies. Our results demonstrate that single-layer SnS, SnSe, GeS and GeSe are candidates to produce on demand spin-current in spintronics applications.

KSIM: simulating KIDSpec, a Microwave Kinetic Inductance Detector spectrograph for the optical/NIR

Abstract KIDSpec, the Kinetic Inductance Detector Spectrometer, is a proposed optical to near-IR Microwave Kinetic Inductance Detector (MKID) spectrograph. MKIDs are superconducting photon counting detectors which are able to resolve the energy of incoming photons and their time of arrival. KIDSpec will use these detectors to separate incoming spectral orders from a grating, thereby not requiring a cross-disperser. In this paper, we present a simulation tool for KIDSpec’s potential performance upon construction to optimize a given design. This simulation tool is the KIDSpec Simulator (KSIM), a Python package designed to simulate a variety of KIDSpec and observation parameters. A range of astrophysical objects are simulated: stellar objects, an SDSS observed galaxy, a Seyfert galaxy, and a mock galaxy spectrum from the JAGUAR catalogue. Multiple medium spectral resolution designs for KIDSpec are simulated. The possible impact of MKID energy resolution variance and dead pixels was simulated, with impacts on KIDSpec performance observed using the Reduced Chi-Squared (RCS) value. Using dead pixel percentages from current instruments, the RCS result was found to only increase to 1.21 at worst for one of the designs simulated. SNR comparisons of object simulations between KSIM and X-Shooter’s ETC were also simulated. KIDSpec offers a particular improvement over X-Shooter for short and faint observations. For a Seyfert galaxy (mR = 21) simulation with a 180 s exposure, KIDSpec had an average SNR of 4.8, in contrast to 1.5 for X-Shooter. Using KSIM the design of KIDSpec can be optimized to improve the instrument further.

Optical Metasurfaces for Energy Conversion.

Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light–matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.

Design of Improved Molecular Solar‐Thermal Systems by Mechanochemistry: The Case of Azobenzene

AbstractMolecular solar‐thermal systems (MOST) have emerged in these last years as a novel concept to store solar light. They rely on two state molecular switches that can absorb a photon to convert the initial state A to a higher‐in‐energy state B. The chemical energy stored by B can be then released to reconstitute A. Although simple in its principle, an optimal MOST needs to satisfy several requirements: incoming photon energy in the solar spectrum range, high photoreaction quantum yield, high storage density, no degradation. The first challenge is therefore the search for molecular switches that accomplish all such properties. Until now, trial‐and‐error experiments have been performed, led by physicochemical intuition. The result is that most of the initially proposed switches have been abandoned in favor of the preferred norbornadiene/quadricyclane system, together with its derivatives. Nevertheless, most of the solar spectrum is still out of the MOST absorption region, hence requiring novel approaches. Here, it is shown how mechanochemistry can be applied to improve the principally desired characteristics of a MOST: photon absorption energy, storage energy, and thermal B‐to‐A energy barrier. It is especially shown how azobenzene—a paradigmatic photoswitch still attracting much attention—can be proposed, within certain limits, as a MOST when applying external forces.

WCu composites fabrication and experimental study of the shielding efficiency against ionizing radiation

A comprehensive study of the present work aimed to investigate the radiation shielding features for W–Cu composites materials with high density. Isostatic hot pressing technique was applied to obtain W85 wt%Cu15 wt% and W75 wt%Cu25 wt% composites with various thickness (0.6, 0.9, 1.2, 1.5 and 2.7 cm). Composites were the pollycristalline samples with well packed microstructure. The statistical grain size distribution performed that the size of an agrolemerated copper grains increases with the Cu content rising. X-ray diffraction (XRD) analysis showed that the main spectrum lines of the composites are corresponded to the bcc phase of tungsten and fcc phase of copper. The linear attenuation coefficient (LAC) was detected experimentally using a NaI detector at various incoming photon energy. The highest values of LAC are found 2.11 and 4.33 cm−1 for W75 wt%Cu25 wt% and W85 wt%Cu15 wt%, respectively, at low energy 0.266 MeV while the lowest values (0.44 and 0.48 cm−1 for W75 wt%Cu25 wt% and W85 wt%Cu15 wt%, respectively) are observed at high energy 1.25 MeV. From the obtained results, it can deduce the discussed W–Cu composites are suitable to be used in several applications of radiation protection.

Multi bin energy-sensitive micro-CT using large area photon-counting detectors Timepix

X-ray micro-CT has become a popular and widely used tool for the purposes of scientific research. Although the current state-of-the-art micro-CT is on a high technology level, it still has some known limitations. One of the relevant issues is an inability to clearly identify and quantify specific materials. The mentioned drawback can be solved by the energy-sensitive CT approach. Dual-energy CT, which is already frequently used in human medicine, offers the identification of two different materials; for example, it differentiates an intravenous contrast agent from bone or it can indicate the composition of urinary stones. Resolving a larger number of material components within a single object is beyond the capabilities of dual-energy CT. Such an approach requires a higher number of measurements using different photon energies. A possible solution for multi bin, or so-called spectral CT, is the application of photon-counting detectors. Photon counting technology offers an integrated circuitry capable of resolving the energy of incoming photons in each pixel. Therefore, it is possible to collect data in user-defined energy windows. This contribution evaluates the applicability of the large-area photon-counting detector Timepix for multi bin energy-sensitive micro-CT. It presents an experimental phantom study focused on the simultaneous K-edge-based identification and quantification of multiple contrast agents within a single object. The paper describes the collection of multiple energy bins using the Timepix detector operated in the photon counting mode, explains the data processing, and demonstrates the results obtained from an in-house implemented basis material decomposition algorithm.

Ion bombardment technique induced alterations in the surface chemical composition and shielding parameters of polymeric material

At present, ion beam technology is one powerful technique to improve the physico-chemical properties of polymeric material. In this work, ultra high molecular weight polyethylene samples were bombarded with 1 MeV He-ion beam at fluences ranging from 1×1013 to 5×1014 ions/cm2. The changes in the chemical composition of the treated layer caused by the ion beam were investigated. The hydrogen escapes due to the ion beam irradiations were measured by the nuclear reaction analysis (NRA) technique using the 1H(15N, αγ)12C reaction. The oxygen uptake has been studied by the Rutherford backscattering spectrometry (RBS) and Fourier transform infrared spectrometer (FTIR) techniques. The partial and total mass attenuation coefficients of photons at energies 81, 356, 511 and 1332 keV were estimated using the XCOM program (version 3.1). The obtained results showed that the hydrogen release was increasing with an increase in ion fluence. Moreover, important oxygen uptake of bombarded samples was also observed. These effects led to significant improvements in the surface characteristics of the treated materials such as changes in the shielding parameters. The changes in the mass attenuation coefficients (μ/ρ) were calculated relying on the incoming photon energies and the atomic concentrations of the elements that are present in the target material. The total atomic cross-sections and effective atomic numbers were calculated by using the data of the total mass attenuation coefficients. A decrease in both the total atomic cross-section and effective atomic numbers was noticed with an increase in the ion beam fluence.

Na2Si3O7/Ag micro and nano-structured glassy composites: The experimental and MCNP simulation surveys of their radiation shielding performances

In the present work, the very low-cost glassy structured sodium silicate (Na2Si3O7) matrix has been reinforced with micro-and nano-sized silver (Ag) particles in different weight percentages. The ionizing radiation shielding performances of the micro and nano-structured composites have been determined experimentally and theoretically for the first time. The experiments have been realized by the gamma-ray spectroscopy setup equipped with NaI(Tl) detector and Ba-133 point radioactive source. The radiation shielding performance has been discussed in the context of mass attenuation coefficient (μ/ρ) half-value layer (HVL), and mean free path (MFP). Besides, the theoretical research related to the radiation shielding ability of the samples has been carried out by using the Monte Carlo N-Particle Transport (MCNP) v6.2© simulation code. Since the experimental values and MCNP findings are very close to each other, MCNP simulation has been extended to a large incoming photon energy interval ranging from 25 keV to 1000 keV for both micro-and nano-structured composites. The particle size effect (PSE) on radiation shielding performance has been investigated and discussed. As a result of PSE research, it has been revealed that the addition of nanoparticles is more effective in the improvement of the radiation shielding for the lowest Ag concentration and low photon energies. Additionally, the radiation shielding capability of the composites has been discussed in the context of ambient dose equivalent, H∗(10) which is one of the operational quantities. By using the ambient dose equivalent definition, the ambient dose rate values of the composites have been calculated for the first time. In conclusion, it has been determined the composites with higher micro-and nano-Ag particle additives have considerably good radiation shielding ability against low energy photons that are mostly utilized in diagnostic and treatment medical applications.

Intrawell and interwell phonon-excitons in a CdS/CdSe/CdS asymmetric quantum well

Binding energies of intrawell and interwell excitons are studied in the CdS/CdSe/CdS asymmetric quantum well by varying right well sizes under polaronic effect. The transition energy, transition life time, oscillator strength and absorption coefficients are measured. The above properties are obtained in the influence of image charge potential included in the Hamiltonian. The optical absorption coefficients with the function of incoming photon energy are obtained. The results bring out that the peak of absorption coefficient is larger for the direct exciton than for the indirect exciton and the radiative lifetime for the indirect exciton is found to be higher.

The assessment of usage of epoxy based micro and nano-structured composites enriched with Bi2O3 and WO3 particles for radiation shielding

This study has been devoted to investigate the radiation shielding performance of epoxy-based micro and nano Bi2O3 and WO3 reinforced composites. While the research has been carried out by using experimental data and MCNP6 simulation for the micro-structured composites; the effect of nano Bi2O3 and WO3 particles addition on the radiation shielding property of epoxy has been discussed by using experimental data. While the gamma-ray spectroscopy experiments have been carried by using NaI(Tl) scintillation detector and Ba-133, Cs-137, and Co-60 sources, the MCNP version 6.2 code has been utilized for the simulation. The experimental and MCNP6 simulation results showed good consistency for both particle reinforcement and different incoming photon energies. Particle size effect investigation also indicated that for both kinds of dopant particles, the nano dopant is more successful in attenuating the intensity of incoming photons than the micro dopant even if they are used in the same percentages. In conclusion, it can be suggested that the micro and nano-structured composites having the highest Bi2O3 and WO3 contents have a considerable potential to shield the harmful effects of some of the diagnostic radionuclides utilized in nuclear medicine as well as the radiation imaging machines such as roentgen, mammography or PET scans.

Relaxation effects on the magnetic cross section and fluorescence radiation polarization after 4d inner-shell photoionization of Ba-like ions

On the basis of the multi-configuration Dirac–Fock method and the density matrix theory treatment of photoionization (PI) dynamics, a systematic investigation for 4d inner-shell PI of exemplary Ba atom and Ba-like Nd4+, Gd8+ and Yb14+ ions is performed. Starting from the general framework of the relativistic, the relaxation effects are considered by using a set of relaxed one-electron orbitals in solving the coupled Dirac equations. Our results uncover for the first time that the relaxation effects, arising from the overlap integrals between orbitals of the initial state and the relaxed final state, may play a paramount role in determining the magnetic sublevel cross sections, the photoelectron angular-distribution asymmetry parameters, and the fluorescence polarizations of the subsequent x-ray radiation, particularly for neutral atoms close to the threshold regime. Yet the importance of inclusion of the orbital relaxation weakens as the incoming photon energy and/or the degree of atom ionization increases. The nature of these influences is explored, which allows us to get more insight on the physical process and mechanism involved. Our results are consistent with those obtained by the experiments and other theoretical predictions.

Measuring gamma doses over the mGy-kGy range with a single type of TLD detector

Thermo-luminescent detectors are currently used to measure gamma doses in the medical and environmental surveillance fields. During the past few years, the CEA Reactor Studies Division tested and validated the use of these detectors for gamma flux characterization and nuclear heating measurements in mixed neutron/gamma fields of low power reactors. Doses were comprised between a few mGy and a few Gy for dose rates up to a few Gy.h-1. However, in MTR or TRIGA reactors, the gamma flux level is much higher (&gt; 1012 n/cm2/s) and the TLD currently in use (CaF2:Mn and 7LiF:Mg,Ti) and their readout protocols were no longer suitable for the resulting doses. In order to extend the applicable dose range up to ∼1 MGy (dose rate of a few kGy.h-1), several options were explored. On one side, some adjustments were made to the readout protocols of CaF2:Mn and 7LiF:Mg,Ti, notably by testing the use of filters to reduce the amount of light received by the reader PMT to avoid saturation. On the other side, a new type of TLD (LiF:Mg,Cu,P) with different Li enrichments (natural or enriched in 7Li) was tested. This paper presents the calibration measurements results performed in pure gamma fields, at the irradiation platform of the CEA Cadarache Radioprotection Division, between 250 mGy and 3 Gy for all detector types. In addition to the calibration, these measurements also studied the Mg,Cu,P-doped detectors response: reproducibility, dose rate dependence, incoming photon energy dependence, high temperature effect when reading TLD, etc. Results show that at low doses Mg,Cu,P-doped TLDs are slightly less stable than CaF2:Mn and 7LiF:Mg,Ti. The sensitivity modification after a high dose exposure seems to indicate that a new protocol readout should be defined for Mg,Cu,P-doped sensors (high temperature peak).

Ta2O5 reinforced Bi2O3–TeO2–ZnO glasses: Fabrication, physical, structural characterization, and radiation shielding efficacy

The melt-quenching method was applied to fabricate a new glass series containing 10Bi 2 O 3 –70TeO 2 -(20-x)ZnO-xTa 2 O 5 , x = 0, 2, 4, and 6 mol%. The chemical compounds were well mixed and melted in a furnace at 900 °C, and then the molten transferred to another furnace at 320 °C for annealing. X-ray diffraction is used to confirm the amorphous phase of the fabricated glasses. Moreover, the fabricated glasses' structure characterization was established using Raman analyses. Besides, the gamma-ray protection capacity was evaluated for the fabricated glass series. Thus, the MCNP-5 simulation code and XCOM software program were utilized to estimate the investigated glass samples' linear attenuation coefficients. The glass sample's highest attenuation coefficient, with 6 mol % of the Ta 2 O 5 doping ratio is ranged between 418.17 and 0.27 cm −1 . In comparison, the fabricated glass without Ta 2 O 5 possesses the lowest attenuation factor and decreased from 359.39 cm -1 to 0.26 cm −1 , raising the incoming photon energy from 0.015 MeV to 15 MeV, respectively. The simulated linear attenuation coefficient was then applied to calculate the half-value thickness, and transmission factor for the incoming photons. The obtained results showed that the fabricated glass samples' shielding ability enhanced with the insertion of the Ta 2 O 5 . • New glass system of chemical composition 10Bi 2 O 3 -70TeO 2 -(20-x)ZnO-xTa 2 O 5 ; where x=0, 2, 4, and 6 mol% have been prepared. • Density and molar volume values were calculated for each synthesized sample by using the Archimedes principle. • Raman spectra were obtained from the region of 100-4000 cm -1 . • Shielding capacity for glass samples have been investigated via MCNP-5 and Xcom.