High Incident Electron Energies Research Articles

The Xe autoionizing states in kinetic energy region (3–14) eV studied at high and low incident electron energies

The Xe autoionizing states in kinetic energy region (3–14) eV studied at high and low incident electron energies

Inclusive electron scattering in the quasielastic region with the Korea-IBS-Daegu-SKKU density functional

With the framework of KIDS (Korea-IBS-Daegu-SKKU) density functional model, the isoscalar and isovector effective masses of nucleon and the effect of symmetry energy in nuclear medium are investigated in inclusive $(e,e')$ reaction in quasielastic region. The effective masses are varied in the range $(0.7 \sim 1.0)M$ with free nucleon mass $M$, and the symmetry energy is varied within the uncertainty allowed by nuclear data and neutron star observation. The wave functions of nucleons inside target nucleus are generated by solving Hartree-Fock equation with adjusting equation of state, binding energy and radius of various stable nuclei, and effective mass of nucleon in the KIDS model. With the obtained wave functions, we calculate the differential cross section for the inclusive $(e,e')$ reaction and compare the theoretical results with Bates, Saclay, and SLAC experimental data. Our model describes experimental data better at SLAC-type high incident electron energy than those measured from Bates and Saclay. The influence of the effective mass and symmetry energy appears to be precise on the longitudinal cross section.

Study of Electron Impact Ionization Cross-Sections of Nitrogen Molecule by Inelastic Collision

In this article, the calculation of ionization cross-section of N2 molecule by electron impact is reviewed. The work on ionization cross-sections from threshold to high (10 KeV) incident electron energies are calculated and their applications are discussed. To find exact values of total ionization cross-sections for the N2 molecule, a semiempirical approach of Jain and Khare (1976) is adopted which is a modification to eliminate the error factors, and then it is compared with the existing experimental and/or theoretical data which gives satisfactory results

A study on the validity of the first Born approximation for high-energy electron scattering with nitrogen molecules

The first Born approximation is one of the most extensively used principles to deal with scattering processes, especially for fast projectiles. In the case of fast electron scattering, an empirical criterion has been proposed and widely accepted that a good match among the fast electron scattering results with higher and higher incident electron energies is enough to demonstrate the validity of the first Born approximation. However, it is found that the mutually agreed experimental generalized oscillator strength of our electron scattering measurement and the cited ones of the and states of nitrogen at a wide range of incident electron energies is obviously smaller than the generalized oscillator strength obtained by our vibronically resolved inelastic x-ray scattering experiment, in which the first Born approximation is always satisfied. Such a phenomenon indicates that the empirical criterion is not strict, and our understanding of electron scattering with multi-electron system is far from complete.

Investigations of the valence-shell excitations of molecular ethane by high-energy electron scattering.

The differential cross sections and generalized oscillator strengths for the low-lying excitations of the valence-shell 1eg orbital electron in ethane have been measured for the first time at a high incident electron energy of 1500 eV and a scattering angular range of 1.5°-10°. A weak feature, termed X here, with a band center of about 7.5 eV has been observed, which was also announced by the previous experimental and theoretical studies. The dynamic behaviors of the generalized oscillator strengths for the 3s (8.7 eV), 3s+3p (9.31 eV, 9.41 eV), and X (∼7.5 eV) transitions on the momentum transfer squared have been obtained. The integral cross sections of these transitions from their thresholds to 5000 eV have been obtained with the aid of the BE-scaling (B is the binding energy and E is the excitation energy) method. The optical oscillator strengths of the above transitions determined by extrapolating their generalized oscillator strengths to the limit of the squared momentum transfer K2 → 0 are in good agreement with the ones from the photoabsorption spectrum [J. W. Au et al., Chem. Phys. 173, 209 (1993)], which indicates that the present differential cross sections, generalized oscillator strengths, and integral cross sections can serve as benchmark data.

On the role of the second-order derivative term in the calculation of convergent beam diffraction patterns

The simulation of (scanning) transmission electron microscopy images and diffraction patterns is most often performed using the forward-scattering approximation where the second-order derivative term in z is assumed to be small with respect to the first-order derivative term in the modified Schrödinger equation. This assumption is very good at high incident electron energies, but breaks down at low energies. In order to study the differences between first- and second-order methods, convergent beam electron diffraction patterns were simulated for silicon at the [111] zone-axis orientation at 20 keV and compared using electron intensity difference maps and integrated intensity profiles. The geometrical differences in the calculated diffraction patterns could be explained by an Ewald surface analysis. Furthermore, it was found that solutions based on the second-order derivative equation contained small amplitude oscillations that need to be resolved in order to ensure numerical integration stability. This required the use of very small integration steps resulting in significantly increased computation time compared to the first-order differential equation solution. Lastly, the efficiency of the numerical integration technique is discussed.

An algorithm for Monte Carlo simulation of bremsstrahlung emission by electrons

An algorithm for Monte Carlo simulation of bremsstrahlung emission by electrons based on the framework of SuperMC is presented in this paper with efficient and accurate methods to sample the angular distribution and energy of bremsstrahlung photons. The photon energy is sampled according to scaled energy-loss differential cross sections tabulated by Seltzer and Berger. A novel hybrid model for photon angular distribution by low- and high-energy incident electrons is developed. The model uses Tsai’s full form of angular distribution function with atomic form factors for high-energy incident electrons. For electrons of <500 keV, a simple efficient and accurate analytical distribution function is developed, using adjustable parameters determined from the fitting of numerical values of the shape functions tabulated by Kissel et al. The efficiency of sampling photon energy is 80%. Our angular sampling algorithm for high-energy electron bremsstrahlung based on Tsai distribution function is very efficient (sampling efficiency ~70%) in the useful photon energy range.

The creation, destruction, and transfer of multipole moments in electron–ion three-body recombination using the Gell-Mann–Goldberger–Watson method

We use the Gell-Mann–Goldberger–Watson (GGW) method to further develop and elaborate on our earlier investigation of electron–ion three-body scattering. The GGW method is used to obtain multipole moment creation, destruction, and transfer rate formulae by the three-body recombination of electrons with ions assuming short-range interaction potentials. This approach leads to the derivation of the rate coefficient formula obtained previously via the alternative wave-packet propagation method. We show how to include exchange effects into the formalism, allowing extension of its validity to lower incident electron energies, and also introduce the Liouville-space formulation. Furthermore, we indicate that this method makes the relevance of the formulae to relativistic systems more transparent, demonstrating its validity for high incident electron energies and heavy ions. The Liouville-space formulation is used to facilitate the derivation of a selection rule for the rate coefficients for cylindrically symmetric plasmas, which is of practical importance for the proper formulation of population-alignment collisional-radiative modeling.

Incident electron energy influence on energy positions and forms of the 3s3p6np autoionising states of Ar

SynopsisEjected electron spectra of Ar have been studied with high resolution at incident electron energies of 41.2 and 505 eV and at the constant ejection angle of 90o. The study was focused on the 3s3p6np states and their behaviour at low and high incident electron energies.

Generalized oscillator strengths for the valence-shell excitations of xenon studied by the high-resolution fast-electron impact

SynopsisUsing the high-resolution fast-electron energy loss spectrometer, the generalized oscillator strengths (GOSs) of the valence-shell excitations of xenon were determined at a high resolution of 70 meV and a high incident electron energy of 1500 eV, and the momentum transfer dependence behaviors of GOSs of the 6s[3/2]1 and 6s'[1/2]1 excitations of xenon are discussed.

Singly and doubly excited states in ejected electron spectra of neon at high incident electron energies

Ejected electron spectroscopy has been used to study singly and doubly excited states of neon at constant incident electron energies between 505 and 2018 eV and ejection angles from 10° to 130° with high resolution in ejected energy range from 12 to 46 eV. The full ejected electron energy range has been studied at two extreme incidence energies and three ejected angles, namely 40°, 90° and 130°. The low energy region (12 to 21.5 eV) has been investigated at 505 eV over the full angular range and at 90° at six incident energies from 505 to 2018 eV. The features in the ejected electron spectra have been attributed to the autoionisation of Ne+ (2s2p 6 nl) excited states and Ne (2s2p 5 nl n′l′ and 2s 22p 4 nl n′l′) double excited autionising states. Lower energy ejected electrons arise from simultaneous excitation of s and p electrons above the second ionisation potential (62.53 eV) while higher energy ejected electrons are coming from singly and doubly excited states. The high resolution and high sensitivity allowed us to see separated singlet from triplet states at high incident energies. Comparison with previous works gives a good agreement in energy positions of measured features. At the highest ejected electron energies only the features coming from double excitation are present, but with very low intensities in the spectra due to the small cross sections and high background. New resonances are found whose classification needs new experimental and theoretical investigations.

Metastable atomic ion production in electron-O2 collisions

Pulsed electron impact ionization, time-of-flight (TOF) spectroscopy and a novel detector are used to study the production of metastable O+ in e-O2 collisions in the electron energy range from threshold to 450eV. Measured fragment ion kinetic energies are in the range 2–20eV. The ions are identified as being in the 2P state within the ground 2p3 configuration. Peak metastable ion production occurs at an electron energy of ∼130eV in agreement with the energy for maximum production of all O+ ions but the fall off in ionization efficiency toward higher incident electron energies is faster in the metastable case.

Dirac R-matrix calculation for electron-impact excitation of S xiii

Context. Sulfur emission lines in the soft X-ray and extreme-ultraviolet regions are observed in a variety of laboratory and astrophys- ical spectra. But accurate electron impact excitation data for S xiii for state-of-the-art NLTE spectral models are scarce. Aims. We calculated electron-impact excitation collision strengths and effective collision strengths of S xiii for transitions among the lowest-lying 98 fine-structure states 1s 2 2lnlcorresponding to principal quantum numbers n = 2,3,4. The effective collision strengths for these transitions were computed over a wide temperature range (log10 Te (K) = 4.53-7.53) for various astrophysical plasma conditions. Methods. We used the fully-relativistic parallel Dirac R-matrix code to calculate collision strengths. To generate target wavefunctions and energy levels for scattering calculations, we employed the GRASP0 multi-configuration Dirac-Fock code for states up to n = 5. Results. The wavefunctions are generated from 27 configurations - 1s 2 2lnl � (n = 2,3,4,5) - giving rise to 166 jjenergy levels. The collision and effective collision strengths among the lowest 98 fine-structure levels are compared with the previous theoretical calculations. The collision strengths for most transitions agree well at higher incident electron energies. Conclusions. The resonant contributions to effective collision strengths are most dominant at lower temperatures.

Model of secondary electron emission at high incident electron energy for metal

The models of the true secondary electron emission and backscattered electron emission for metal are provided, based on the physical process of secondary electron emission from metal at high incident electron energy. The formula for the true secondary electron yield at high incident electron energy is derived with the Bethe equation known to provide accurate and simple analytical expressions for the stopping power and the probability that a secondary electron produced in a material reaches the surface and is emitted into the vacuum. The formula for the backscattered electron yield at high incident electron energy is derived with the absorbing rule for the incident electron in the material. All the above results lead to a new model for secondary electron emission from metal at high incident electron energy. The secondary electron yields of Au, Ag, Cu and Al derived with the new model are in good agreement with the results obtained from the scatters process simulation code-Casino.

High-resolution electron energy loss spectroscopy of anions chemisorbed on electrode surfaces: The effect of counter cations

In the course of experiments that included Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS) on cation exchange at benzoquinone sulfonate chemisorbed on a Pd(111) electrode, it was found that, whereas the AES spectra remained invariant as the counter cation was varied from H+ to K+ to Cs+, profound changes occurred in the HREELS spectra. Specifically, the intensity of the spectral features decreased noticeably when H+ was replaced with K+. And, when the K+ ions were exchanged with Cs+, nothing but a flat-line (dead) spectrum was observed; even the elastic peak was completely attenuated. When the Cs+ ions were displaced by protons, the initial undiminished spectrum was fully restored. This outcome, while unrelated to cation-exchange selectivity, is of exceptional significance in surface electron spectroscopy. It appears that the positive ions on the surface attracted the low-energy incident electrons such that backscattering towards the energy analyzer was hindered; partially by K+ but totally by the larger Cs+ ion. The use of HREELS to examine the molecular integrity of chemisorbed anionic species must thus take cognizance of the possibility that the counter cation chosen to preserve interfacial-layer electroneutrality can have a profound effect. To circumvent such complication, low-valent and small-radii cations will have to be employed. In addition, although subject to instrument limitations, higher incident-electron energies could be adopted. AES, with incident-electron energies in the kV range, is impervious to the presence of counter cations.

Degrees of polarization of the two strongest5f→3dlines following electron-impact excitation and dielectronic recombination processes of Cu-like to Se-like gold ions

Cross sections for electron-impact excitation and capture to individual magnetic sublevels of Cu-like to Se-like gold ions have been calculated by using a fully relativistic distorted-wave (RDW) method. These magnetic cross sections have further been used to obtain the degrees of linear polarization for the first two strongest $5f\ensuremath{\rightarrow}3d$ radiative lines. A detailed comparison has been made between polarizations of these lines from the electron-impact excitation process and those of the same lines but from the dielectronic recombination process. It is found that for a Cu-like gold ion the polarization in the electron-impact excitation process increases sharply before starting to decrease at higher incident electron energies, and it reaches the maximum at around twice the threshold energy. The situations for other gold ions are very similar. However, as for the dielectronic recombination process, the polarization changes among a very large range with different gold ions. Therefore, the obvious differences between the polarizations from different formation processes can be employed in diagnosing the formation mechanism of the corresponding lines.

Electron distributions in nonlinear Compton scattering

Based on quantum theory, we investigate the distribution of the electrons scattered in the nonlinear Compton effect by an electromagnetic plane wave. The monochromatic case, examined in detail, reveals features of the electron distribution that are useful in the understanding of the pulsed plane-wave case for particular intensity and electron energy regimes. The graphs displayed focus on the case of a head-on or nearly head-on collision of an energetic electron with an electromagnetic circularly polarized pulsed plane wave and show that the deviation in direction is extremely small, while the distribution in energy can be visibly different from that of the initial electron. Two pulse shapes, several laser intensities, and high incident electron energies are considered.

高能原电子对铝和金射程的表达式

高能原电子对铝和金射程的表达式

Shape-controlled nanopores in single crystals

Nanometer length-scale holes (nanopores) are often formed in amorphous materials forfundamental studies of molecular mass transport. In the current study, electron beamirradiation in the transmission electron microscope was used to form nanopores in acrystalline material (Si). Analysis of the nanopores showed that they are formed byknock-on of atoms by the high energy incident electron beam, and surface diffusion ispartially responsible for the hour-glass shapes that are found for some nanopores.Energetically favorable three-dimensional shapes of nanopores were simulated, and thenanopores simulated in the model crystalline material were found to be more stable thanthe nanopores simulated in the amorphous material. The nanopore shape was also found todepend on the nanopore diameter-to-length ratio. Based on the above, we demonstrate theadvantage in using a crystalline material for nanopore formation and show that control ofthe three-dimensional shape of nanopores formed by electron beam irradiation is possible.

Low‐ target optimization for spatial resolution improvement in megavoltage imaging

Recently, several authors have shown contrast improvements in megavoltage portal imaging and cone-beam computed tomography using low atomic number (Z) targets. This work compliments previous studies by investigating the effects of varying different beam production parameters including target atomic number, target thickness, and incident electron energy on spatial resolution. Target materials of beryllium, aluminum, and tungsten were investigated over a range of thicknesses between 10% and 100% of the continuous slowing down approximation range of electrons. Incident electron kinetic energies of 4.5 and 7.0 MeV were used, in conjunction with custom targets installed above the carousel of a modern radiotherapy linear accelerator. Monte Carlo simulations of the accelerator were constructed and compared to the experimental results. The results showed that thinner targets, as well higher incident electron energies, generally produce more favorable modulation transfer function (MTF) curves. Due to an MTF dependence of the detector system on the photon energy, the experimental results showed that low-Z targets produced superior MTF curves. Simulations showed 14.5% and 21.5% increases in f50 for the 7.0 and 4.5 MeV targets (A1; 60% R% CSDA), respectively, when moved from the carousel to the location of the clinical target. f50 values for the custom targets were compared to the clinical 6 MV beam and were found to be between 10.4% lower (4.5 MeV/W) and 15.5% higher (7.0 MeV/Be). Integration of low-Z external targets into the treatment head of a medical linear was achieved with only minor modifications. It was shown that reasonably high resolution images on par or better than those acquired with the clinical 6 MV beam can be achieved using external low-Z targets.