Low Incident Energies Research Articles

Electronic screening effects during bremsstrahlung of carbon atoms and ions

Bremsstrahlung, as an important radiation process in atomic physics, has significant applications in the fields of astrophysics, plasma physics, magnetic and inertial confinement fusion. In this work, the relativistic partial-wave expansion method is used to investigate the bremsstrahlung of neutral carbon atoms and different charged carbon ions scattered from intermediate- and high-energy relativistic electrons, with special attention paid to the electronic screening effect produced by the target electrons. The target wave function is obtained from the Dirac-Hartree-Fock self-consistent calculations, and the electron-atom scattering interaction potential is constructed in the central-field approximation. By solving the partial-wave Dirac equation, the continuum wave functions of the relativistic electron are obtained, from which the bremsstrahlung single and double differential cross sections can be calculated via the multipole free-free transitions between the incident and exit free electrons. The target electronic screening effects on the bremsstrahlung single and double differential cross sections are analyzed under a variety of conditions of incident electron energy and emitted photon energy. It is shown that the target electronic screening effect will significantly suppress the cross sections both at low incident energy and in the soft-photon region. Such a suppressing effect decreases with the incident electron energy and the emitted photon energy gradually increasing. Overall, the electronic screening effect has no significant influence on the shape function of bremsstrahlung.

Emission of high rovibrational hydrogen molecules under detached plasma conditions by recycling on the tungsten wall

Abstract It is well known that the rate coefficient of molecular-assisted recombination (MAR) varies by several orders of magnitude depending on the rovibrational states of the hydrogen molecules. A molecular dynamics simulation is performed to estimate the rovibrational states of recycled hydrogen molecules at the divertor in the JA-DEMO reactor under detached plasma conditions. The simulation results reveal that molecules in high rovibrational states are released even with low incident energy, which will be the dominant condition under detached plasma conditions. Molecules generated in this way can strongly affect the formation of the detached plasma via a molecular assisted-process such as MAR.

Predictions on new Cu-based ABO3 (A=Cu and B=Lu, Y) oxide-perovskite for energy storage and optoelectronic applications: A DFT study

Cu-based novel oxide-perovskite ABO3(A = Cu and B=Lu, Y) compounds have been investigated for their physical properties using the Generalized Gradient Approximation and Revised-Perdew-Burke-Ernzerhof (GGA-RPBE) exchanging correlation-functional within the density functional theory (DFT). The calculations show that both compounds comprise a cubic structure with the space group of Pm3m. The calculations also indicate that the results we have discovered represent unique compounds. Formation enthalpy computations have been used to assess the overall structural stability of both compounds. The density of states and band structure graphs for both perovskite compounds provide strong evidence of their semiconducting behavior. In-depth research is also done on optical properties such as the refractive index, extinction coefficient, absorption, reflectivity, electrical conductivity, and the energy loss function. At high-energy photons, both compounds CuLuO3 and CuYO3 show outstanding conductivity and absorption. While, at lower incident photon energy intervals, they both exhibit transparency. Based on our electronic and optical properties investigations, we have found that CuLuO3 and CuYO3 are potential candidates for use in high-energy UV, and optoelectronic technologies.

Free Infragravity Waves on the Inner Shelf: Observations and Parameterizations at Two Southern California Beaches

AbstractNumerical predictions of nearshore waves and shoreline runup are usually initialized on the inner shelf, seaward of the surfzone, with sea‐swell (SS) waves from local wave buoys or regional wave models. Lower frequency infragravity (IG) waves are not reliably measured by buoys or included in regional models. Here, co‐located pressure and velocity observations are used to characterize IG waves in 10–15 m depth in southern California. Shoreward propagating IG waves are often dominated by free waves, with the boundwave energy fraction <30% for moderate and low energy incident SS waves. Only 5% of records, with energetic long swell, show primarily bound waves. The shoreline slope of concave beaches increases by ∼3 between spring high and low tides, and free seaward and shoreward IG energy in 10–15 m vary tidally. The observed linear dependency of free IG energy on SS energy and period is consistent with Ardhuin et al. (2014, https://doi.org/10.1016/j.ocemod.2014.02.006)'s parameterization (R2 = 0.71). Including the tide level as a proxy for beach slope and modifying the SS frequency dependency increases R2 to 0.91. The ratio of free seaward to shoreward propagating IG energy suggests between 50 and 100% of the energy radiated seaward in depths of 10–15 m is trapped offshore and redirected shoreward. Free (random phase) and bound (phase‐coupled) IG waves are combined to initialize the SWASH numerical model. SWASH predicted runup is only weakly influenced by waves at the offshore boundary. Nonlinear IG generation and dissipation in the shoaling and surfzone overwhelm the effects of shoreward propagating waves observed at the offshore boundary.

Simulation Study of Crystalline Al2O3 Thin Films Prepared at Low Temperatures: Effect of Deposition Temperature and Biasing Voltage

In this paper, classical molecular dynamics simulations were used to explore the impact of deposition temperature and bias voltage on the growth of Al2O3 thin films through magnetron sputtering. Ion energy distributions were derived from plasma mass spectrometer measurements. The fluxes of deposited particles (Ar+, Al+, and O−) were categorized into low, medium, and high energies, and the results show that the films are dominated by amorphous Al2O3 at low incident energies without applying bias. As the deposition temperature increased, the crystallinity of the films also increased, with the crystals predominantly consisting of γ-Al2O3. The crystal content of the deposited films increased when biased with −20 V compared to when no bias was applied. Crystalline films were successfully obtained at a deposition temperature of 773 K with a −20 V bias. When biased with −40 V, crystals could be obtained at a lower deposition temperature of 573 K. Increasing the bias enables the particles to have higher energy to overcome the nucleation barrier of the crystallization process, leading to a greater degree of film crystallization. At this stage, the average bond length between Al-O is measured to be approximately 1.89 Å to 1.91 Å, closely resembling that of the crystal.

Electron Energy-Loss Spectroscopy Method for Thin-Film Thickness Calculations with a Low Incident Energy Electron Beam

In this study, the thickness of a thin film (tc) at a low primary electron energy of less than or equal to 10 keV was calculated using electron energy-loss spectroscopy. This method uses the ratio of the intensity of the transmitted background spectrum to the intensity of the transmission electrons with zero-loss energy (elastic) in the presence of an accurate average inelastic free path length (λ). The Monte Carlo model was used to simulate the interaction between the electron beam and the tested thin films. The total background of the transmitted electrons is considered to be the electron transmitting the film with an energy above 50 eV to eliminate the effect of the secondary electrons. The method was used at low primary electron energy to measure the thickness (t) of C, Si, Cr, Cu, Ag, and Au films below 12 nm. For the C and Si films, the accuracy of the thickness calculation increased as the energy of the primary electrons and thickness of the film increased. However, for heavy elements, the accuracy of the film thickness calculations increased as the primary electron energy increased and the film thickness decreased. High accuracy (with 2% uncertainty) in the measurement of C and Si thin films was observed at large thicknesses and 10 keV, where tλ≈1. However, in the case of heavy-element films, the highest accuracy (with an uncertainty below 8%) was found for thin thicknesses and 10 keV, where tλ≤0.29. The present results show that an accurate film thickness measurement can be obtained at primary electron energy equal to or less than 10 keV and a ratio of tλ≤2. This method demonstrates the potential of low-loss electron energy-loss spectroscopy in transmission electron microscopy as a fast and straightforward method for determining the thin-film thickness of the material under investigation at low primary electron energies.

Fabrication of 208Pb and 193Ir targets on Al-backing using high/ultra-high vacuum deposition technique for low-energy nuclear reaction experiments

Aiming to study the interplay of different nuclear reactions at low incident energies, thin targets of enriched stable isotopes, 208Pb and 193Ir, have been fabricated at the target development laboratory of the Inter-University Accelerator Centre (IUAC), New Delhi. As a means of preparing a large number of thin isotopically pure targets, physical vapour deposition techniques, (a) resistive heating, for fabrication of 208Pb targets of mass thickness 160-340μg/cm2, and (b) electron-gun evaporation technique, for fabrication of 193Ir targets of mass thickness 17-60μg/cm2, have been employed. The fabricated targets were characterized using Rutherford Backscattering Spectrometry (RBS) and Field Emission Scanning Electron Microscopy (FE–SEM). The thickness of targets was estimated based on the evaporation rate and measured by RBS. The RBS was employed to analyse the samples for trace- and heavy impurities, provided the measurements and analysis suggest that the targets prepared in the present work do not contain any impurities. FE-SEM was employed to examine the surface morphology and microstructure in high resolution. This technique enables the detection of any morphological changes induced by the irradiation process, offering insights into the effects of irradiation on the target films. The targets have been successfully deployed to measure complete and incomplete fusion excitation functions, mass distribution of fission fragments, and forward ranges of target-like recoils in 12C + 208Pb, 193Ir reactions from sub- to above barrier energies. Preliminary data analysis suggests the achievement of high-quality 208Pb and 193Ir target foils.

Terahertz Time-Domain Spectroscopic Characteristics of Typical Metallic Minerals

Accurate identification and understanding of various metallic minerals are crucial for deciphering geological formations, structures, and ages. Giving their pivotal role as essential natural resources, a microscopic exploration of metallic minerals becomes imperative. Traditional analytical methods, while helpful, exhibit certain limitations. However, terahertz time-domain spectroscopy, distinguished by its high signal-to-noise ratio, expansive frequency band, and low incident wave energy, is a promising complement to conventional techniques in characterizing metallic minerals. This study employs terahertz time-domain spectroscopy to examine samples of Stibnite, Sphalerite, Galena, and Pyrite originating from diverse geological conditions. The vibrations of molecules within these metallic minerals induce discernible changes in the terahertz spectra. Our findings untiate the extensive potential of terahertz time-domain spectroscopy in the characterization of metallic minerals, affirming its considerable practical value in mineral resource exploration.

Double-differential cross sections for charged particle emissions from α particle impinging on Al at 230 MeV/u

ABSTRACT Charged particle production from α particle fragmentation reactions was investigated experimentally by measurement of 230-MeV/u α particles bombarding an aluminum target. Double differential cross sections were measured for each ejectile of p, d, t, 3He, and 4He using counter telescopes composed of Si surface barrier detectors and crystal scintillators, which were located at laboratory angles between 15° and 60°. The obtained data were analyzed for comparison with data observed at lower incident energies. The results found the following common characteristics: (1) spectra of proton- and neutron-emission are similar in high energy region at forward angle, (2) triton-to-3He ratio of α-breakup yield is 1:2, which is similar to lower incident energy experiment, and (3) the shape of broad peak formed by 3He and α particles could be explained by the process with collision between induced α particle and target nucleus.

UAV Remotely-Powered Underground IoT for Soil Monitoring

This article introduces a practical approach to wirelessly charge underground Internet of things (UIoT) for soil monitoring using ultra high frequency (UHF) radio energy. In the proposed system, UIoT nodes do not require batteries or any aboveground attachments (e.g., solar panel). Instead, they harvest 915MHz radio energy emitted from an unmanned aerial vehicle (UAV) for semi-perpetual operation. The UIoT nodes utilize the harvested energy to measure soil parameters and transmit data back to the UAV using ZigBee protocol. After collecting the data from UIoTs, the UAV uploads it to a cloud server for online soil quality analysis. The system has been optimized for efficient operation, with a UAV transmit power as low as 2 watts. Startup, drive, and power management circuits have been designed to ensure reliable operation of UIoT nodes, even with low incident energy. According to experimental results, the developed RF-UIoT system can successfully power up and transmit more than 1 kilobyte of data within 10 seconds of wireless charging, followed by an additional 1.7 kilobytes of data every 1.6 seconds thereafter.

Plane polarisation in Comptonization process: A Monte Carlo study

Abstract High energies emissions observed in X-ray binaries (XRBs), active galactic nuclei (AGNs) are linearly polarised. The prominent mechanism for X-ray is the Comptonization process. We revisit the theory for polarisation in Compton scattering with unpolarised electrons and note that the ( $k \times k^{\prime}$ )-coordinate (in which, ( $k \times k^{\prime}$ ) acts as a z-axis, here k and k′ are incident and scattered photon momentum, respectively) is more convenient to describe it. Interestingly, for a fixed scattering plane the degree of polarisation PD after single scattering for randomly oriented low-energy unpolarised incident photons is $\sim$ 0.33. At the scattering angle $\theta$ = 0 or $\theta \equiv$ [0,25 $^{\circ}$ ], the modulation curve of k′ exhibits the same PD and PA (angle of polarisation) of k, and even the distribution of projection of electric vector of k′ ( $k^{\prime}_{e}$ ) on perpendicular plane to the k indicates same (so, an essential criteria for detector designing). We compute the polarisation state in Comptonization process using Monte Carlo methods with considering a simple spherical corona. We obtain the PD of emergent photons as a function of $\theta$ -angle (or alternatively, the disc inclination angle i) on a meridian plane (i.e. the laws of darkening, formulated by Chandrasekhar (1946, ApJ, 103, 351) after single scattering with unpolarised incident photons. To explore the energy dependency we consider a general spectral parameter set corresponding to hard and soft states of XRBs, we find that for average scattering no. $\langle N_{sc}\rangle$ $\sim$ 1.1 the PD is independent of energy and PA $\sim 90^{\circ}$ ( $k^{\prime}_{e}$ is parallel to the disc plane), and for $\langle N_{sc}\rangle$ $\sim$ 5 the PD value is maximum for $i=45^{\circ}$ . We also compare the results qualitatively with observation of IXPE for five sources.

An accurate prediction of electronic structure, mechanical stability and optical response of BaCuF3 fluoroperovskite for solar cell application

This study utilizes the first-principles modelling approach based on the density functional theory (DFT) framework to investigate the structural, mechanical, and optoelectronic properties of the BaCuF3 fluoroperovskite. Initially, the three distinct cubic structures of BaCuF3 were simulated based on the positioning of F atoms. This investigation aimed to determine the most stable configuration for BaCuF3. The structural stability of all compounds has been evaluated through the formation enthalpy calculations. In addition, the mechanical stability is assessed by the investigation of elastic stiffness constants. The mechanical stability of the α-BaCuF3 and β-BaCuF3 compounds has been observed. However, the γ-BaCuF3 compound is deemed unstable due to its failure to meet the Born-stability criterion (C44 < 0). The ductility of α-BaCuF3 and the brittleness of β-BaCuF3 have been determined by exploring Pugh's and passion ratios and the Cauchy pressure. The electronic characteristics have been evaluated by examining electronic band structure, density of states and partial density of states. The compounds α-BaCuF3 and β-BaCuF3 have been seen to have indirect and direct band gaps of 0.14 eV (M–Γ) and 1.22 eV (Γ–Γ), respectively. Several optical parameters have been calculated and compared. The materials that have been chosen exhibit significant optical conductivity and absorption coefficients when exposed to high-energy photons while also demonstrating transparency at lower incident photon energy ranges. Our investigations into the optical properties have determined that α-BaCuF3 and β-BaCuF3 exhibit favourable characteristics for solar cell implementation, high-frequency UV, and optoelectronic devices.

The Excitation of the 3D and 4D States of Atomic Hydrogen by Electron Impact

The excitation cross-sections of the 3D and 4D states of atomic hydrogen at low incident energies (from 0.90 to 5.00 Ry) were calculated using the variational polarized orbital method, which is also called the hybrid theory. Up to 12 partial waves (L = 2 to 13) were used to obtain converged cross-sections at high energies. The importance of the long-range forces near the threshold region and the behavior of the cross-sections in that region are indicated. The S, P, and D cross-sections are needed if the total excitation cross-sections are measured in addition to the elastic cross-sections. These cross-sections are also useful if the cascade from the D to the P to the S states is considered in the diagnostics of solar and astrophysical observations.

Direct or Precursor-Mediated? Mechanisms for Methane Dissociation on Pt(110)-(2 × 1) at Both Low and High Incidence Energies.

The activation of alkanes on metal catalysts may involve a precursor-mediated mechanism, in which impinging molecules are first trapped on the catalyst surface to form an adsorbed precursor and may undergo extensive excursion on the surface in search of an active site. A characteristic feature of such a mechanism is an increasing initial sticking probability (S0) with decreasing incidence energy at low incidence energies. Indeed, such "negative activation" was observed on the reconstructed Pt(110)-(2 × 1) surface with a missing row structure. In this paper, we describe an extensive theoretical investigation of methane dissociation on Pt(110)-(2 × 1) using a machine-learned high-dimensional potential energy surface (PES) based on a first-principles training data set. Quasi-classical trajectories (QCTs) are calculated on the PES to simulate the dissociation of both CH4 and CHD3 at various incidence energies. The agreement with the measured initial sticking probabilities is shown to be substantially improved for high incidence energies when compared to previous theoretical studies, indicating a better characterization of the dissociation barrier. Additional QCT calculations have been carried out for the trapping and diffusion of CHD3 under experimental conditions at low incidence energies. The trapping probability is shown to increase with decreasing incidence energy, consistent with the experimentally observed "negative activation" below 10 kJ/mol. The reactivity of the trapped methane is attributed to the combined effect of its nonthermal diffusion across the surface Pt rows and the lowered barrier reached by surface thermal fluctuation. These simulations shed valuable light on the microscopic dynamics of the initial and often rate-limiting step in heterogeneous catalytic processes involving alkanes.

Competition between ion beam sputtering and self-organization of point defects for surface nanostructuring on germanium

Nanostructuring via ion beam irradiation on Ge substrates can be activated by ion beam sputtering and self-organization of point defects (SPDs). For evaluating the mechanism by which these formation factors compete, we studied nanostructuring on Ge substrates subjected to sputtering-dominant conditions, viz., the low-energy ion incidence. A focused ion beam was used for nanostructuring and adjusting an angle of ion incidence to the surface normal range of 0°–60°. The ions accelerated for irradiation were Ga+ with an incident energy of 5–30 keV, and the fluence and beam current were 1 × 1020–1 × 1022 ions/m2 and 0.5–16.7 nA, respectively. Based on the results of serial experiments, the incident energy of 5 keV can be the threshold for the activation of nanostructuring by SPD.

Power flow in magnetically insulated transmission lines with ion backscatter effects

Ion backscattering off of surfaces in magnetically insulated transmission lines (MITLs) is often ignored in kinetic simulations of MITL power flow. Backscattering reduces ion current losses and the surface impact heating, which dictates the rate at which surface-adsorbed contaminants are liberated into the anode–cathode gap. Backscatter probabilities are difficult to implement in a kinetic code because there are limited data for incident ion energies less than a few keV. This paper presents an analytic model based on the Rutherford scattering formula that reproduces the measured backscatter probabilities at high incident energies and transitions to the highly reflective behavior expected at low incident energies. The backscatter model is implemented in power flow simulations, which are validated with current loss experiments conducted on the 0.4 TW Mykonos accelerator at Sandia National Laboratories. This simulation setup is then used in a high-current Z-machine shot. Backscatter effects are found to be unimportant in the low-current Mykonos regime but significantly reduce current losses at the Z-machine scale.

High-energy interference-free K-lines synchrotron X-ray fluorescence microscopy of rare earth elements in hyperaccumulator plants.

Synchrotron-based micro-X-ray fluorescence analysis (µXRF) is a non-destructive and highly sensitive technique. However, element mapping of rare earth elements (REEs) under standard conditions requires care, since energy-dispersive detectors are not able to differentiate accurately between REEs L-shell X-ray emission lines overlapping with K-shell X-ray emission lines of common transition elements of high concentrations. We aim to test REE element mapping with high-energy interference-free excitation of the REE K-lines on hyperaccumulator plant tissues and compare with measurements with REE L-shell excitation at the microprobe experiment of beamline P06 (PETRA III, DESY). A combination of compound refractive lens optics (CRLs) was used to obtain a micrometre sized focussed incident beam with an energy of 44 keV and an extra-thick silicon drift detector (SDD) optimised for high-energy X-ray detection to detect the K-lines of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr) and neodymium (Nd) without any interferences due to line overlaps. High-energy excitation from La to Nd in the hyperaccumulator organs was successful but compared to L-line excitation less efficient and therefore slow (∼10-fold slower than similar maps at lower incident energy) due to lower flux and detection efficiency. However, REE K-lines do not suffer significantly from self-absorption, which makes XRF-tomography of millimetre-sized frozen-hydrated plant samples possible. The K-line excitation of REEs at the P06 CRL setup has scope for application in samples that are particularly prone to REE interfering elements, such as soil samples with high concomitant Ti, Cr, Fe, Mn, Ni concentrations.

Magnetic field effect on the linear and nonlinear refractive index and optical absorption of a donor in a GaAs quantum ring

The effects of the magnetic field (γ), the radial position of impurity and the degree of confinement on the oscillator strength (OS), refractive index and optical absorption (α) of an impurity inside a GaAs quantum ring (QR) are explored using the effective mass approximation and variational method. It is shown that the peak position of the optical absorption and the refractive index decrease and move toward the lower incident photon energy as the strength of the γ increases. In addition, it is found that the strongest α relates to the case when the impurity is positioned at the right side of QR in the presence of the magnetic field. Our examinations also show that the oscillator strength decreases as the γ increases especially for an on-center donor impurity.

High responsivity and multi-wavelength response photodetector based on single bandgap AlInN film by magnetron sputtering

The AlInN film with a band gap of 2.96 eV is prepared on glass by radio frequency magnetron sputtering. Photoluminescence spectra reveals that the emission band is originated from both the band-edge and some defect-related radiation. The interdigital AlInN photodetector based on metal−semiconductor−metal (MSM) structure exhibits photoresponse characteristics from ultraviolet to visible light. The defect energy level is responsible for the multi-wavelength response of the low-energy incident irradiation light. The photodetector exhibits the best performance under 660 nm illumination, with a responsivity of 102 A/W, an external quantum efficiency of 190% and a specific detectivity of 2.8 × 109 Jones. These three factors improve by 4–6 orders of magnitude compared to point electrodes. The AlInN MSM interdigital electrode structure provides a relatively promising candidate structure for achieving high-performance multi-wavelength photodetectors.

Perturbation on atomic alignment of Ag L3-subshell by multiple ionization for heavy ions impact

Alignment of silver ion after electron in L3-subshell ionized by 1H+, 4He2+, 40Ar12+ and 129Xe30+ ions impact respectively are reported. Low incident energy range is investigated to explore collision-induced alignment in case of strong Coulomb deflection effect. Characteristic L X-ray spectra are measured in emission angle range of 115∘-155∘. For Lα and Lβ2 lines, anisotropy parameter β is determined respectively and then converted to degree of alignment A20 by taking anisotropy coefficient α and Coster-Kronig (CK) correction coefficient κ into account. The measured atomic alignment is compared to theoretical prediction basing on semiclassical model and satisfactory agreement is observed only for light ions impact. While the dealignment coefficient is determined to be 0.98, 0.71 and 0.30 for 4He2+, 40Ar12+ and 129Xe30+ ions impact at (vp/vL3)2=0.011, respectively. This work demonstrates the strong dealignment due to multiple ionization for heavy ions impact even in ultra low incident energy regime.