Atomic Number Research Articles

Positron stopping in multilayer materials.

Positron annihilation spectroscopy provides a sensitive toolset for defect characterization. In beam based studies of single-layer targets, the form of implantation profiles is well established, depending on the kinetic energy and angle of incident positrons relative to the target surface and the density and average atomic number of the target. For multilayer systems, the difference in density and across the layers makes derivation of an analytical form difficult. To date, the determination of positron stopping profiles in multilayer targets has primarily involved Monte Carlo simulations.
We present here an alternative approach that estimates the energy distribution dN/dE of those positrons transmitted past each layer boundary, by fitting the remaining tail of the stopping profile after each layer with a basis set comprised of calculated stopping profiles in the same material they are transmitted through. The stopping profile in the next layer is then found by summing a series of stopping profiles in the new medium in proportion to the determined distribution dN/dE. The results of our model are compared with simulation results in a system of alternating layers of Al and Au and find reasonable agreement in the predicted profile and excellent agreement in the predicted mean implantation depth. Lastly, we derived a simple formula-based approach for the calculation of the mean implantation depth in two-layer systems that provides results in excellent agreement with the full model.

Integrating gold nanostars into condensed DNA.

Integrating gold nanostars into condensed DNA.

Investigation of some attenuation and interaction ionizing radiation parameters of selected human tissues

This study aims to calculate and analyze different radiation interactions and attenuation parameters through 22 types of human tissues. Mass attenuation coefficient (MAC), half value layer (HVL), total cross section (δT), and effective atomic number (Zeff) for photon energy across the spectrum band 0.0595–1.33 MeV were observed. These parameters were obtained through the EPICS 2017 software. Fast neutron removal cross section (FNRCS) at 4.5 MeV and macroscopic removal cross section (MRCS) were calculated by Phy-X/PSD and MRCScal software, respectively. In addition, electronic, nuclear linear energy transfer (dE/dx) and ranges (R) of H+, He++, and Au+ energetic ions were evaluated with SRIM Monte Carlo software across a wide energy range of 0.0011–20 MeV. Moreover, the CSDA range and total stopping power (TSP) of energetic electron 0.01–1000 MeV interaction through the selected human tissues were calculated by the ESTAR NIST program. The cortical bone has the highest Zeff values, while the adipose tissue has the lowest values across all energies over the interesting photon energy (0.0595–1.33 MeV). The descending order of ion ranges is RH+ > RHe++ > RAu+ through the investigated tissues. Gamma-ray dose rate (Dr) values through bone (men), bone (women), and cortical bone three tissues are higher than other selected tissues. The attenuation parameters are essential input values in estimating not only the dose and exposure in radiotherapy and medical diagnostic imaging but also in the proper design of photon shield material.

Analytical modeling of atomic-number-dependent electronic stopping cross sections in Si, C, 4H-SiC, Al, Ni, and Ag

Abstract Atomic number (Z 1) dependences of electronic stopping cross sections (S e) for channeling trajectories had been well explained for low-velocity ions; however, this is not the case with S e for random trajectories (S e random). We modeled the difference between the effective atomic number for random trajectories and that for channeling ones (Z’) changing linearly with the difference between the actual atomic number and Z’. The proportionality constant k for S e random in Al, Ni, and Ag for 1.8×108 cm s−1 ions was found to depend little on the target atomic number. k for S e random in 4H-SiC for 1.5×108 cm s−1 ions, on the other hand, located between k for S e random in Si for 1.5×108 cm s−1 ions and k determined from that for 1.4×108 cm s−1 ions in C and that for 2.0×108 cm s−1 ions in C.

Quantitatively Profiling the Evolution of Hydrogen Storage and Defect Healing Processes in Palladium at the Nanoscale.

Light elements or compounds with an average atomic number (Z) of less than 10 are difficult to detect due to their weak interactions with electrons and photons. Here, we introduce a direct thermal absorbance measurement platform for scanning electron microscopy. The technique, named ZEM, is particularly sensitive to low Z materials, including hydrogen (Z = 1) and vacancy (Z = 0). We use Pd as an example to explore ZEM's potential in characterizing hydrogen storage materials. ZEM reveals that hydrogen storage is highly inhomogeneous, concentrating on grain boundaries and defects. ZEM also unveils a large defect density created by hydrogenation, uncovering abundant voids beneath the surface. ZEM's nondestructive detection method allows us to investigate multiple hydrogen charging-discharging cycles, revealing two distinct hydrogen uptake phenomena accompanied by unusual defect healing processes. We further establish the causality between hydrogenation and defect formation, quantifying distinct correlations between hydrogen-induced defect generation and defect-mediated hydrogen trapping. The rich phenomena discovered by the ZEM underscore its potential in material characterizations, particularly for light elements or compounds.

Enhancement of Photoluminescence Quantum Yield of Silver Clusters by Heavy Atom Effect.

Many ligand-protected metal clusters exhibit phosphorescence at room temperature. However, strategies for improving their phosphorescence quantum yield, a critical parameter of performance, remain poorly developed. In contrast, fluorescent dyes are commonly modified by introducing heavy atoms, such as iodine (I), to enhance intersystem crossing in the excited state, thereby harnessing the heavy atom effect to increase phosphorescence efficiency. In this study, a pair of ligand-protected silver (Ag) clusters is successfully synthesized with internal cavities encapsulating anions (Xz -), namely sulfide ions (S2-) or iodide ions (I-), which significantly differ in atomic number each other. Single-crystal X-ray diffraction and nuclear magnetic resonance spectroscopy revealed that the resulting Ag clusters are composed of X@Ag54S20(thiolate)20(sulfonate)m, where (X, m) = (S, 12) or (I, 11). X-ray photoelectron spectroscopy revealed that the Ag atoms in these compounds exhibit a mixed-valence state. Furthermore, experiments on their photoluminescence revealed that a heavy central anion induced an internal heavy-atom effect similar to that observed in organic fluorescent dyes. As a result, the phosphorescence quantum yield became 16 times higher when S2- is replaced by I- as the central atom.

Efficacy of dual-layer spectral detector computed tomography for detecting early ischemic changes in patients with acute ischemic stroke: A pilot study

Objectives: This study evaluated the efficacy of dual-layer spectral detector computed tomography (DLCT) for detecting early ischemic changes (EICs) in patients with acute ischemic stroke (AIS), focusing on electron density (ED) and effective atomic number (effective Z) imaging. Material and Methods: This retrospective study included 15 patients (mean age: 76.5 ± 9.8 years) with AIS who underwent non-contrast computed tomography (CT) with DLCT and magnetic resonance imaging (MRI) on the same day. Quantitative analysis was performed to compare conventional CT, ED, and effective Z values between the infarcted and contralateral brain regions. Qualitative assessment was conducted by two radiologists using the modified Alberta Stroke Program Early CT Score methodology. Receiver operating characteristic curve analysis was performed to evaluate diagnostic performance, and kappa statistics were used to assess interobserver agreement. Results: Significant differences were observed in the conventional CT and ED values (P < 0.01) but not in effective Z values (P = 0.46) between the infarcted and contralateral regions. ED imaging demonstrated superior diagnostic accuracy (area under curve [AUC] = 0.90) compared with conventional 120-kVp CT (AUC = 0.85) and effective Z imaging (AUC = 0.62). Furthermore, interobserver agreement (kappa = 0.71) was better for ED imaging than for conventional 120-kVp CT (kappa = 0.65). Qualitative analysis revealed that ED images showed better agreement with MRI findings and higher interobserver consistency than conventional 120-kVp images. Conclusion: Compared with conventional CT, DLCT with ED imaging significantly enhanced detection of EICs in AIS

Lanthanum-doped zinc borate glasses: fabrication, structural analysis, thermal properties, and gamma radiation shielding performance

Zinc borate glasses with a composition formula of (60-m)B₂O₃–40ZnO–mLa₂O₃ (m = 0, 3, 6, 9, 12, and 15 mol%) were synthesized via the melt-quenching technique for the purpose of investigating the effects of La₂O₃ incorporation on their structural, thermal, and radiation shielding properties. Amorphous structures for all samples (coded as ZBLa0 to ZBLa15) were confirmed using X-ray diffraction and Differential thermal analysis. Incorporating La₂O₃ significantly influenced the glass matrix, increasing density, molar volume, thermal expansion and the glass transition, while decreasing the crystallization peak temperature and thermal stability. These effects highlight La₂O₃'s role as a network modifier that depolymerizes the glass structure, as indicated by shifts in FT-IR bands and altered vibrational modes. Radiation shielding properties improve markedly with La₂O₃ addition, as evidenced by increased mass attenuation coefficients and effective atomic numbers, making the glass with 15 mol% La₂O₃ (ZBLa15) particularly effective at gamma-ray attenuation across a wide photon energy range. These findings suggest that La₂O₃-doped zinc borate glasses are highly suitable for applications requiring enhanced radiation shielding alongside reliable thermal performance.

A study on the mechanical and radiation shielding characteristics of concrete samples reinforced with brass alloy and boron carbide.

A study on the mechanical and radiation shielding characteristics of concrete samples reinforced with brass alloy and boron carbide.

Evaluation of folic acid-targeted gadolinium-loaded perfluorohexane nanodroplets on the megavoltage X-ray treatment efficiency of liver cancer.

Evaluation of folic acid-targeted gadolinium-loaded perfluorohexane nanodroplets on the megavoltage X-ray treatment efficiency of liver cancer.

Probing the fine structures of low atomic number catalysts by using electron energy loss spectroscopy

Probing the fine structures of low atomic number catalysts by using electron energy loss spectroscopy

Cavity QED in a high NA resonator.

From fundamental studies of light-matter interaction to applications in quantum networking and sensing, cavity quantum electrodynamics (QED) provides a toolbox to control interactions between atoms and photons. The coherence of interactions is determined by the single-pass atomic absorption and number of photon round-trips. Reducing the cavity loss has enabled resonators supporting 1 million roundtrips but with limited material choices and increased alignment sensitivity. Here, we present a high-numerical aperture, lens-based resonator that pushes the single-atom single-photon absorption probability near its fundamental limit, reducing the mode size at the atom to order λ. This resonator provides a single-atom cooperativity of 1.6 in a cavity where the light circulates ∼10 times. We load single 87Rb atoms into this cavity, observe strong coupling, and demonstrate cavity-enhanced atom detection with fidelity of 99.55(6)% and survival of 99.89(4)% in 130 μs. Introducing intracavity imaging systems will enable cavity arrays compatible with Rydberg atom array computing technologies, expanding the applicability of the cavity QED toolbox.

Tuning the Radiation Shielding Properties of Lead and Bismuth-Modified Borotellurite Glasses

Abstract This study investigated the radiation shielding properties of gamma photons for lead and bismuth-modified borotellurite glasses at certain energy values in the 0.122–0.867 MeV range. The investigated glasses' mass attenuation coefficient (MAC) was evaluated, with the results revealing that the MAC of all the samples was the highest at 0.122 MeV. The glass sample with lowest percentage concentration of Bi2O3 and PbO2 has lower MAC than the other glasses. The glasses' linear attenuation coefficient varied in the 4.579–8.273 cm-1 range at 0.122 MeV, with the results emphasizing that Bi2O3 and PbO2 addition leads to an improvement in the glasses' radiation shielding effectiveness. Investigation of the glasses' half-value layer (HVL) found a decrease with increased density. The HVL varied between 1.92 and 2.49 cm at 0.779 MeV. A positive relation between the Bi2O3 and PbO2 amount and the glasses' attenuation performance was found through the effective atomic number (Zeff) results, with the highest Zeff recorded for the glass with 11 mol% of both Bi2O3 and PbO2. The transmission factor (TF) of the glasses was calculated, with the results demonstrating an improved attenuation ability with increased sample thickness, and as the Bi2O3 and PbO2 concentration increased, the TF values decreased.

α-decay half-lives calculations with Killingbeck potential

In this paper, we propose a new analytical solution of the [Formula: see text]-decay process for the Killingbeck potential with the spherical Coulomb potential and determine the half-lives of some [Formula: see text]-emitters with atomic number [Formula: see text] located in the region [Formula: see text] using the Wentzel–Kramers–Brillouin (WKB) approximation. The Killingbeck potential, with its complex form including harmonic and linear confinement terms, offers a greater richness of interaction and nuclear shape. We provide a solution to the problem of multiple turning points by showing that they can be reduced to two nonsymmetric points. Results obtained show relationships between the paramater of the nuclear potential and experimental data. Those results are compared with experimental data and other theoretical results from the literature. We find that our results are in very good agreement with the experimental data.

Application of total quadratic indices of molecular pseudographs: a study on Nonsteroidal Anti-Inflammatory Drugs (NSAIDs) to predict physicochemical properties using weighting schemes

Abstract This study investigates the relevance of physicochemical properties of 34 NSAIDs to their chemical characteristics using total quadratic indices $q_k(x)$ modeled as pseudographs with atomic number and atomic radius weighting schemes, compared against traditional indices modeled using unweighted graphs. The objective was to assess the predictive capabilities of these indices in modeling drug properties. Multiple Ordinary Least Squares (OLS) regression revealed significant multicollinearity in the models. Principal Component Analysis (PCA) was employed to address this issue, leading to a reduction in multicollinearity, although it was accompanied by a slight decrease in model performance metrics such as \( R^2 \). Despite this, quadratic indices demonstrated competitive performance when compared to traditional indices. Notably, the quadratic indices showed higher relevance in predicting the physicochemical properties complexity (C), molecular weight (MW), refractivity (RV) and polarizability (P) compared to traditional indices. The model validated by parameters like coefficient of determination ($R^{2}$), $p$ - value, standard error (S.E), F-statistic and Durbin-Watson (DW) statistics. These results underscore the potential of quadratic indices in enhancing predictive modeling of drug properties, offering improved insights compared to traditional topological indices.

Accuracy of a whole-body single-photon emission computed tomography with a thallium-bromide detector: Verification via Monte Carlo simulations.

Single-photon emission computed tomography (SPECT) devices equipped with cadmium-zinc-telluride (CZT) detectors achieve high contrast resolution because of their enhanced energy resolution. Recently, thallium bromide (TlBr) has gained attention as a detector material because of its high atomic number and density. This study evaluated the clinical applicability of a SPECT system equipped with TlBr detectors using Monte Carlo simulations, focusing on 99mTc and 177Lu imaging. This study used the Simulation of Imaging Nuclear Detectors Monte Carlo program to compare the imaging characteristics between a whole-body SPECT system equipped with TlBr (T-SPECT) and a system equipped with CZT detectors (C-SPECT). The simulations were performed using a three-dimensional brain phantom and a National Electrical Manufacturers Association body phantom to evaluate 99mTc and 177Lu imaging. The simulation parameters were accurately set by comparing them with the actual measurements. The T-SPECT system demonstrated improved energy resolution and higher detection efficiency than the C-SPECT system. In 99mTc imaging, T-SPECT demonstrated 1.71 times higher photopeak counts and improved contrast resolution. T-SPECT exhibited a significantly lower impact of hole tailing and higher-energy resolution (4.50% for T-SPECT vs. 7.34% for C-SPECT). Furthermore, T-SPECT showed higher peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) values, indicating better image quality. In 177Lu imaging, T-SPECT showed 2.76 times higher photopeak counts and improved energy resolution (3.94% for T-SPECT vs. 5.20% for C-SPECT). T-SPECT demonstrated a higher contrast recovery coefficient (CRC) and contrast-to-noise ratio (CNR) across all acquisition times, maintaining sufficient counts even with shorter acquisition times. Moreover, T-SPECT acquired higher low-frequency values in power spectrum density (PSD), indicating more accurate internal image reproduction. T-SPECT offers superior energy resolution and detection efficiency than C-SPECT. Moreover, T-SPECT can provide higher contrast resolution and sensitivity in clinical imaging with 99mTc and 177Lu. Furthermore, the Monte Carlo simulations are confirmed to be a valuable guide for the development of T-SPECT.

Evaluation of Radiation Shielding Effectiveness of Some Metallic Alloys Used in the Nuclear Facilities

Abstract Several nuclear shielding parameters were evaluated for surgical stainless steel grades 304, 304 L, 316, and 316 L. The effective atomic number Zeff, mean free path (MFP), effective electron density Neff, half-value layer (HVL), and effective conductivity (Ceff) of the investigated alloys were evaluated via the mass attenuation coefficient (μ/ρ). The mass attenuation (μ/ρ) coefficients were computed for gamma-ray photons in the energy range from 15 keV to 15 MeV using Phy-X/PSD program. Fast neutron attenuation was analyzed by computing the removal cross section (ΣR, cm−1) using partial density method. The obtained results by Phy-X/PSD program were validated using NIST XCOM and Monte Carlo (MCNP4C) code. The stopping power of these alloys against electron/proton/α-particles was evaluated using the ESTAR and SRIM Monte Carlo code, considering total stopping power and projected range. Furthermore, the transmitted neutron fraction at different neutron energies was calculated using Neutron Calculatro-V2 code. These calculations were performed for thermal neutrons (25.4 eV) and fast neutrons (with energies of 4 and 4.5 MeV). The obtained results showed that 316 L alloy possesses good protection performance against gamma photons, charged particles, fast and thermal neutrons compared with other investigated alloys. Comparison of the calculated values revealed good agreement between Phy-X/PSD, NIST XCOM, and MCNP4C. This work should be informative for the potential uses of these materials in the nuclear industry to build effective radiation shielding.

Radiation shielding properties of xPbF2−20Na2O−10CaO−(70−x) B2O3 glass system

The influence of PbF2 incorporation on the physical and radiation shielding properties of six glass samples, labeled BPbF0 to BPbF25, was investigated. These samples have a composition of xPbF2−20Na2O−10CaO−(70−x) B2O3 where (0≤x≤25 in 5 mol.% increments). The physical parameters, including density and molar volume, were calculated. As PbF2 content increased, the density rose significantly from 2.476 g/cm³ to 4.077 g/cm³, attributed to the substitution of low molecular weight B2O3 with high molecular weight PbF2. Similarly, the molar volume increased from 26.95 cm³/mol to 27.138 cm³/mol, indicating the formation of non-bridging oxygen atoms and the expansion of the glass network. X-ray diffraction (XRD) analysis confirmed the amorphous nature of the samples, as no crystalline peaks were observed. Gamma radiation shielding parameters were theoretically evaluated using Phys-X/PSD software. The mass attenuation coefficient (MAC) and linear attenuation coefficient (LAC) were found to increase with higher PbF2 content at a given energy. Both coefficients decreased linearly between 0.015 and 0.08 MeV with increasing energy, remained nearly constant in the range of 1 to 3 MeV due to Compton scattering, and increased gradually beyond 3 MeV due to pair production. The half-value layer (HVL) and mean free path (MFP) decreased as PbF2 content increased, reflecting improved shielding efficiency. Furthermore, the effective atomic number (Zeff) and effective neutron density (Neff) also increased with higher PbF2 content. Compared to commercial glasses like RS-360 and various concretes, the prepared glass system demonstrated superior gamma-ray shielding properties. These findings suggest that the developed glass system is highly effective for gamma radiation shielding applications.

Striking Differences in Regulating Effects on Electronic Transport of 2D Iodine-Based Devices from Metal and Nonmetal Dopants.

Two-dimensional iodine-based materials, characterized by unique structures and properties, hold immense potential in electronics. Here, research indicates that doping metal/nonmetal dopants with small atomic numbers can substantially improve the equilibrium electronic transport of the new-type 2D iodine-based device. Unlike metal dopants, such enhancement from nonmetallic dopants varies greatly among elements, including sites. N doping remarkably exhibits the best enhancement. Essentially, small site doping, especially nonmetallic dopants, shows strong orbital hybridization with effective overlap, resulting in optimized distribution of electronic states and electrostatic potential and the formation of more efficient conduction channels, further enhancing the density of states (DOS) and electron transmission. In nonequilibrium, all dopants generally enhance conductance under lower biases but weaken conductance under higher biases. Such enhancement is much more pronounced in nonmetallic-doped devices in small sites, and in metallic elements, it is only achieved in Al. These devices all show increased currents with bias. The current of the undoped device can be weakened by doping metallic elements at higher voltages. At any voltage, N-small doping always maintains the optimal enhancement on current, and Mg doping almost retains the best weakening effect. Findings provide valuable theoretical guidance for such a 2D iodine material in high-performance tunable electronic devices and sensors.

XRF-Escape Scintillator Footprints for Nuclear Medicine Imaging and Gamma-Ray Spectrometry

The present paper introduces the so-called scintillator footprints, consisting of plots showing XRF-escape peaks and their relative emission intensities in the energy range of interest for nuclear medicine SPECT and PET. A footprint describes the suitability of a scintillator for quantitative investigation with the best possible detectability. Sixteen scintillation materials have been identified in the literature, characterized by effective atomic numbers Zeff ranging between 22 and 75. The footprints of NaI:Tl and BGO, confirm the best suitability for quantitative spectral analysis in SPECT and PET, at 140.5 keV and 511 keV, respectively. Moreover, for the low-Zeff scintillators like CaF2 and CMSM, the XRF-escape effect is to predict irrelevant even at 140.5 keV due to the small energy value of X-ray fluorescence.