Modifications in high energy higher order Born approximation

A systematic study is made to find out the differential scattering cross-section in the case of electron-atom collisions. The first and the second Born terms ofO(1/k _i ) are calculated in the framework of Yates high energy higher order Born approximation. The second Born term ofO(1/k _i ² ) is calculated using the second order Wallace term, the third term is calculated using the Glauber-eikonal series of Yates. The method is applied to the elastic scattering of electrons by atomic hydrogen in the energy range 100–400 eV and by helium for energies 200 eV and 400 eV. Comparison is made with other theoretical results and the experimental data.     

电子与钠原子散射的S, T, U参数研究

电子原子散射中的S，T，U参数可用来描述散射前后自旋状态的变化，研究精细结构水平上的散射激发振幅之间的关系，进而揭示电子原子碰撞过程中电子自旋-轨道耦合以及电子-电子交换等自旋相关效应.采用扭曲波玻恩近似计算了钠原子受电子散射S→P跃迁中的S，T，U参数，分析了多种入射能(2.2—60 eV)的电子与钠原子激发S→P跃迁过程的S,T,U参数随散射角的分布，其中对10 eV入射能的S_p参数与已报道实验数据符合一致.结果表明，较低能电子入射下的S,T,U参数随散射角的分布幅度和起伏都比较明显，入射能大于40 eV的电子入射，S,T,U参数的散射角分布变化很小. 关键词： 散射激发 S')" href="#">S T')" href="#">T U参数')" href="#">U参数 散射振幅 自旋相关效应     

Amorphous germanium III. Optical properties

The optical properties of thick sputtered films (～30μ) of amorphous Ge, grown with different substrate temperatures (0ˇ-T _sˇ-350°C), were obtained between 0·05 and 4·5 eV by a combination of reflectance, transmittance and ellipsometric measurements. The refractive index at 0·15 eV decreases monotonically with increasing T _s, or equivalently, with increasing density, and is 4·13±0·05 eV in the highest density films. The absorption edge is approximately exponential (10²?α?10⁴ cm^?1) but shifts monotonically to higher energy and increases in slope with increasing T _s. Similarly, the peak in ε₂ grows by about 10% and shifts by about 0·15 eV to higher energies, reaching a maximum of about 23 at 2·90±0·05 eV in the high density films. The peak in the transition strength ω²ε₂ occurs at 4·2±0·2 eV in all films, but increases in magnitude with increasing T _s. The sum rules for n _eff(ω) and ε_0,eff(ω) are evaluated for ▄ω?5 eV and vary monotonically with T _s. These trends are neither compatible with Galeener's void resonance theory nor with changes in the oxygen content of the films, determined by the examination of absorption peaks at 0·053 eV and 0·09 eV. An explanation, suggested here and expanded in I, is based on the observed changes in the structure of the network and voids.     

Positronium formation by electron capture from hydrogen-like ions

Two different impulse approximations are provided for the problem of fast positron collisions with hydrogen-like ions. One of the impulse approximations is formulated by making a consistent expansion of the scattering wave function in powers of the weak interaction to the strong. The other impulse approximation is formulated by making a consistent expansion of theT-matrix in powers of the weak interaction to the strong. In this impulse approximation, the opposite limits of the target nuclear charge tending to zero and to infinity are examined. Differential and angle-integrated cross sections are computed for ground-state positronium formation from hydrogen within the impulse approximations. The full peaking approximation is employed in the evaluation of theT-matrix. By 300 eV, the impulse approximations for the angle-integrated cross section are in close agreement with the strong potential Born and the exact second Born calculations.     

Models for the heavy rare earth metals and (rare earth) Fe2 compounds involving 5d and 6s electrons

A model involving 5d electrons is introduced to explain the differences between the observed saturation moments in the heavy rare earth metals and those of the corresponding tripositive ions. Atomic 5d states, whose energies are determined by 4f–5d and spin-orbit interactions, are assumed to be broadened into partly overlapping bands with individual widths of the order of 1 eV. The 5d electrons produce negative contributions to the hyperfine fields but positive or near zero contributions to the magnetic moments. It is postulated that the 5d electrons are transferred from the rare earth ions to those of the iron in the (Rare Earth) Fe₂ compounds. This leads to increases in the magnetic hyperfine fields because the negative 5d contributions are lost, but in detailed application of the model increases in the 6s contributions also play a large part. Published energy level and wave function analyses for atomic Gd, Tb, Dy, Er and Tm are used in order to apply the theory to these materials.     

Theoretical investigation on photovoltaic properties of PC61BM‐PDPP5T system as a promising polymer‐based solar cell

In the current work, dependent density functional theory and time‐dependent density functional theory calculations coupled with the inherent charge hopping model and some visualization techniques have been used to systematically investigate the photovoltaic properties of PC₆₁BM‐PDPP5T system. Calculations show that PC₆₁BM‐PDPP5T system possesses the relatively large open‐circuit voltage 0.82 V the middle‐sized exciton binding energy (0.690 eV), the small internal reorganization energy (0.159 eV) in the exciton‐dissociation process, but the relatively large one (0.396 eV) in the case of charge‐recombination. With a simplified molecular model, the exciton‐dissociation rate constant, k_dis, is estimated to be as large as 1.156 × 10¹⁰ s^?1 in PC₆₁BM‐PDPP5T phase interface, while the charge‐recombination one, k_rec, is only 1.018 × 10⁷ s^?1 under the same condition, which indicates a rapid and efficient photoinduced exciton‐dissociation process. Copyright © 2016 John Wiley & Sons, Ltd.     

Triple differential cross section of electron impact ionisation of Na(3s, 3p, 3d)

The fivefold differential cross section (5DCS) of the ionisation by electron impact of atomic sodium is determined theoretically for its fundamental 3s(² S) state and the excited 3p(² P) and 3d(² D) states by a procedure which employs in the transition matrix element of the first order Born approximation, the correlated double continuum (3C) wave function. This permits us to determine the statistical M-state population and the orientation and alignment tensors in (e,2e) detection. It is also shown that, the use of Gamow correlation term, in the independent particle (2C) model, reproduces, only in some situations, the shape of the angular distribution of the 5DCS obtained by the (3C) wave function. Received: 17 November 1997 / Received in final form: 16 March 1998 / Accepted: 21 March 1998     

9Be(3He,n)11C and 11B(3He,n)13N Reactions at Energies below Coulomb Barrier

Angular distributions have been measured for ⁹Be(³He, n)¹¹C and ¹¹B(³He, n)¹³N reactions for the neutron group leading to the ground state at E_3He = 0.90, 1.00, 1.20, 1.40 MeV and 1.70, 1.90 MeV respectively. To fit the experimental data, the theory of two nucleon stripping reactions below the Coulomb barrier has been considered. Taking Coulomb distorted wave functions for the interacting particles in the initial channel, a closed analytical form for the differential cross-section has been obtained. The other two cases using the plane wave Born approximation and the distorted wave Born approximation are also applied to the experimental data. The agreement between the Coulomb distorted wave calculations and the experimental data is better than with the PWBA and DWBA. The spectroscopic factors are extracted by fitting the experimental data with the theoretical calculations.     

Electron impact excitation of hydrogen and helium in Coulomb-projected Born methods

Coulomb-projected Born methods for the theoretical study of electron impact excitation of hydrogen and helium are reviewed. The results obtained by using different forms of Coulomb-projected Born methods are compared with other theoretical and experimental results and analyzed. The inadequacy of the variable charge Coulomb-projected Born approximation (VCCPB)—the most recent form of the Coulomb-projected Born methods—in giving good results in processes where exchange is dominant is discussed in detail. The ‘modified’ VCCPB approximation obtained by modifying the VCCPB method to remove its shortcomings is also discussed and its application to electron impact excitation of 2³ s state of helium is studied.     

2S-excitation of atomic hydrogen by electrons at intermediate energies

The method of Das developed recently to analyse elastic scattering of electrons by atoms has been extended in the present paper to inelastic scatterings. The method has been applied for the computation of 2S-excitation, cross-sections at two typical intermediate energiesviz. 54.4 eV and 100 eV energies. Some of the results are compared with available experimental results and are found to be in satisfactory agreement with these.     

Elastic cross sections of 1s-muonic atoms at low energies in non-adiabatic approach

The low-energy elastic cross-section in collisions of a muonic atom with the hydrogen isotope is investigated, employing a new wave function (trial) and using the coordinate-space Faddeev–Hahn model. The wave function includes non-adiabatic terms. Our results of s–wave cross-sections are given, at the tμ(1s) + d scattering. Calculated cross-sections are in good accord with the results published by Chiccoli et al., while having no good agreement with other recent reports.     

High energy elastice + − O2 scattering

Theoretical differential cross-sections are obtained for the elastic scattering of fast (E _i ⩾ 200 eV) positrons by oxygen molecules. Employing the independent atom model, the atomic scattering amplitudes are calculated with the (static + polarization) model potentials, in the partial wave analysis (PWA). Comparisons made with the theory and experiments on the incident electrons, show significant differences at small angles.     

Electron-stimulated desorption of sodium atoms from oxidized molybdenum

The time-of-flight technique combined with a surface-ionization-based detector has been used to investigate the yield and energy distribution of sodium atoms escaping in electron-stimulated desorption (ESD) from adlayers on the surface of molybdenum oxidized to various degrees and maintained at T=300 K as functions of incident electron energy and surface coverage by sodium. The sodium-atom ESD threshold is about 25 eV, irrespective of sodium coverage and extent of molybdenum oxidation. Molybdenum covered by an oxygen monolayer exhibits secondary thresholds at ∼40 eV and ∼70 eV, as well as low-energy tailing of the energy distributions, its extent increasing with surface coverage by sodium Θ. The most probable kinetic energies of sodium atoms are about 0.23 eV, irrespective of the degree of molybdenum oxidation and incident electron energy at Θ=0.125, and decrease to 0.17 eV as the coverage grows to Θ=0.75. The results obtained are interpreted within a model of Augerstimulated desorption, in which adsorbed sodium ions are neutralized by Auger electrons appearing as the core holes in the 2sO, 4sMo, and 4pMo levels are filled. It has been found that the appearance of secondary thresholds in ESD of neutrals, as well as the extent of their energy distributions, depend on surface coverage by the adsorbate. Fiz. Tverd. Tela (St. Petersburg) 40, 768–772 (April 1998)     

Observation of the paramagnetic resonance of Fe in Pd

The observation of the paramagnetic resonance of Fe in Pd is reported. The ion is found to be in an S tate. We deduce the s wave exchange parameter to be 0.056 ± 0.046 eV and the d wave parameter to be 0.0025 ± 0.0002 eV in good agreement with results for Mn in Pd and with resistivity results for Fe in Pd.     

Electronic structure,optical dielectric constant and born effective charge of EuAlO3

EuAlO₃ (EAO) is synthesized by the sol–gel process. The Rietveld refinement of the X-ray diffraction data shows that the material has orthorhombic structure with Pbnm space group. The density functional theory calculations are initiated with the experimental lattice parameters. The full potential linearized augmented plane wave method and projector augmented wave method are used to investigate the ground state properties of EAO. An indirect band gap of 1.8 eV is observed with the valence band maximum at the Γ point and the conduction band minimum at the R point. The X-ray photoemission spectroscopy (XPS) spectra of EAO are obtained in the energy window of 0–1000 eV. Using the electronic density of states, the valence band (VB) spectrum of EAO is generated and compared with the observed VB-XPS spectrum. The optical dielectric constant and the refractive index of the material are calculated for the photon energy radiation. The optical properties show a considerable anisotropy in the material. The Born effective charge of various elements and the dielectric tensor of EAO have been calculated.     

Design of Sandwich Transducer Based on the Equivalent Length Algorithm

The sandwich transducer structure is comprised of three components along its main axis: the back metal cap, piezoelectric ceramic stack and the horn. The purpose of this work is to present a simplified method, referred as the equivalent length algorithm, to design the actuator parameters including each segment length and the resonance frequency f_s. The actuator length L and the propagation wavelength λ along its main axis satisfy the standing wave theory. So, define an equivalent length coefficient for each part of the actuator, and then the sandwich structure is regarded as a single material cylindrical rod with equivalent length L′. According to the standing wave theory, the equivalent length L′ of the actuator can be determined with the given resonance frequency f_s, or vice versa. The phase length of each part of the actuator in the standing wave is optimized freely in the design procedure. The actual length of each part of the actuator is determined by the equivalent length coefficient. Finally, the resonance frequencies of three given actuators are calculated with this method. They are compared with those obtained through Ansys simulation and those measured by an impedance analyzer. The results show agreement.     

Elastic scattering of electrons by benzene

Relative differential cross-sections for the elastic scattering of electrons from benzene have been measured at incident energies 300, 500, 700 and 900eV and for scattering angles between 30° and 120°. The results are discussed and compared with the independent atom model (IAM) calculations. Two different sets of scattering amplitudes for the constituent atoms of benzene were used in these calculations, one obtained from first Born approximation and the other from partial wave analysis of the Dirac equation. Only the static interaction was taken into account in the calculations. The higher the incident energy, the better is the observed agreement between experiment and theory. This indicates that at higher energies, absorption, exchange and polarization effects are not significant as compared to the static interaction and that the IAM satisfactorily predicts the interference of scattering from the individual atoms of C₆H₆.     

Collision between two ortho-positronium (Ps) atoms: A four-body Coulomb problem

The elastic collision between two ortho-positronium (e.g. S = 1) atoms is studied using an ab-initio static exchange model (SEM) in the centre of mass (CM) frame by considering the system as a four-body Coulomb problem where all the Coulomb interaction terms in the direct and exchange channels are treated exactly. A coupled channel methodology in momentum space is used to solve Lippman–Schwinger equation following the integral approach. A new SEM code is developed in which the Born–Oppenheimer (BO) scattering amplitude acts as input to derive the SEM amplitude adapting the partial wave analysis. The s-, p- and d-wave elastic phase shifts and the corresponding partial cross-sections for the spin alignment S = 0, i.e., singlet (+) and S = 2, i.e., triplet (?) states are studied. An augmented Born approximation is used to include the contribution of higher partial waves more accurately to determine the total/integrated elastic cross-section (σ), the quenching cross-section (σ_q) and ortho-to-para conversion ratio (σ/σ_q). The effective range theory is used to determine the scattering lengths and effective ranges in the s-wave elastic scattering. The theory includes the non-adiabatic short-range effects due to exchange.     

Theoretical Analysis of Double Differential Cross Sections for n+ 238U Reaction

Based on the new measurements of total, nonelastic, elastic cross section and elastic scattering angular distributions for n+U reactions, a set of neutron optical model potential parameters is obtained in the region of incident neutron energy from 0.1 to 20 MeV. The cross sections, angular distributions, energy spectra and double differential cross sections are calculated and analyzed by optical model, nuclear fission theory, distorted wave Born approximation theory, coupled channel theory, the unified Hauser-Feshbach theory, as well as exciton model. The results indicate that our theoretical model can reasonably analysis n+ ²³⁸U reaction data with neutron energy lower than 20 MeV.