Nature of coherent enhancement of inelastic electron scattering from disordered media

The mechanism of weak localization of relatively fast electrons scattered with a fixed energy loss from disordered media is examined. The main focus of this paper is to put forward an explanation for why coherent enhancement of electron scattering in the inelastic-scattering channel takes place at angles which differ from π. A simplified kinematic model is proposed to determine the basic properties of the weak localization of electrons in the inelastic scattering channel. The model easily reproduces the range of scattering angles typical for the weak localization of electrons with fixed energy loss. The procedure does not require calculation of the contribution from the crossed diagrams. The results agree with those based on the dynamical theory associated with the calculation of the crossed and ladder diagrams. It is possible to follow the transition from the weak localization of the new type to the ordinary weak localization with decreasing energy loss. The weak localization of the new type is in accord with the weak localization of regular type if the energy loss is about the energy of an optical phonon.     

Diffuse LEED intensities of disordered crystal surfaces: II. Multiple scattering on disordered overlayers

The diffraction of low energy electrons from disordered overlayers adsorbed on ordered substrates is treated theoretically by an extension of Beeby's multiple scattering method. A lattice gas model is assumed for the disordered adsorbate layer. Multiple scattering within a certain area around each atom — each atom of the overlayer and within the ordered substrate — is treated self-consistently, the remaining contributions to the total scattering amplitude being averaged. The theory can be used in the limiting cases of random distribution and of long range order within the adsorbate layer.     

Elastic and inelastic scattering of positrons from hydrogenlike ions

Summary The total elastic cross-sections of the collisions of positrons with various hydrogenlike targets (with nuclear chargeZ=1, 2, 3, 4, 5 and 11) are determined at 13 values of the incident energy lying below 6.8 e V(the positronium formation threshold of e⁺-H scattering). The inelastic scattering of positrons by the same targets is investigated for the first time at energies above the positronium formation thresholds. Both scattering processes are treated using a coupled-static formalism and an iterative Green's function partial wave expansion technique. The resulting cross-sections demonstrate the stability of this technique and emphasize the importance of exploring the aspects of positron-ion collisions more fundamentally on both theoretical and experimental levels.     

Elastic and inelastic scattering of nucleons from 16O

Measurements of differential elastic and inelastic cross sections for neutron scattering from ¹⁶O at incident energies 18 to 26 MeV are presented. In addition to cross sections for neutron scattering differential cross sections for proton scattering up to 66 MeV are described in terms of phenomenological optical model potentials. At 24.5 MeV incident energy inelastic scattering up to 11.5 MeV excitation was measured. The elastic and inelastic compound nucleus contributions were examined. Direct inelastic scattering from the normal parity states was calculated using the DWBA and coupled-channel formalisms. The inelastic scattering cross section from non-normal parity state 2⁻ was calculated using the coupled-channel formalism via multi-step processes. Cross sections due to inelastic scattering from some of the states, which are thought to be members of an excited state rotational band were calculated using both vibrational and rotational approaches and were compared.     

Deep inelastic electron scattering from the deuteron

In the present lectures we discuss the role of nuclear structure effects in deep inelastic scattering of leptons on the deuteron. Also a problem of unfolding the neutron structure functions, spin-independent and spin-dependent, from the combined proton-deuteron data is considered.Lectures given (by the first author) at the Indian-Summer School on Electron Scattering of Nucleons and Nuclei, Prague (Czech Republic), September 1994.On leave from Bogoliubov's Laboratory of Physics, JINR, Dubna 141980, Russia.This work was supported in part by the Natural Sciences and Engineering Research Council of Canada. One of the author (LPK) wishes to thank NSERC for an international scientific exchange award that made it possible to visit the University of Alberta.     

Focussed inelastic resonances in particle scattering from surfaces

Particles, such as atoms or electrons, inelastically scattered from a crystal surface in resonance with a bound state are predicted to focus around a discrete set of final angles with a defined energy for each angle. The final angle and energy of such focussed inelastic resonances (FIR) are shown to be independent of the initial state. A calculation of the FIR amplitude indicates favorable conditions for the observation of the so far elusive bound states of He on low-index metal surfaces and of image states on stepped metal surfaces.     

Elastic electron scattering from C and O

Electron scattering cross sections for carbon and oxygen between q = 1 fm⁻¹ and 4 fm⁻¹ are given. The data are analysed in terms of a phenomenological charge distribution and new information concerning the tail and the center of the charge distribution are obtained. The presence of dispersion effects appears to be necessary to explain the cross sections in the first diffraction minimum. The effect of a finite potential and short range correlations on the form factor are discussed.     

Elastic and inelastic positron-helium scattering

Elastic and inelastic positron--helium scatterings have been investigated with the coupled-channel optical method (CCO). Ionization continuum and positronium formation channels are included via a complex equivalent-local optical potential. Calculations are reported of cross sections of elastic scattering, total excitation and n=2, 3, and 4 excitations of ground-state helium for incident energies from 30~eV to 400~eV. The present calculation shows that the ionization and Ps-formation channels significantly affect the cross sections of elastic and inelastic positron--helium scatterings.     

Elastic electron scattering from 19F

The form factors for elastic scattering from ¹⁹F have been calculated with a projected Hartree-Fock function obtained from a calculation in which the B1 force of Brink and Boeker was used as two-body interaction. Good agreement was obtained with the experimental data, both for the charge and for the magnetic form factor. A detailed analysis of the results shows that the agreement depends in an essential way on the amount of 0d component in the wave function of the valence nucleons.     

弹性波在固体自由粗糙平界面上的散射

利用散射幅度矩阵的概念来处理弹性波在粗糙界面弹性介质中的散射问题。利用微扰近似解边界方程,对散射幅度进行求解,得到了散射幅度的0阶、1阶和2阶解。同时分析了粗糙起伏高度符合高斯分布时,散射幅度的数学期望值和方差,它们分别代表平均场和声场在偏离镜面方向的起伏。最后进行了实验。     

Elastic and inelastic scattering of 185 MeV protons from 12C

The polarization of 185 MeV protons in elastic scattering and in the excitation of the 2⁺ state at 4.44 MeV and the 0⁺ state at 7.65 MeV in ¹²C has been measured in the angular region 2°–60°. Optical model calculations are performed for the elastic scattering. Angular distributions for the inelastic scattering from the 2⁺ state at 4.44 MeV and the 3^? state at 9.64 MeV are calculated in the distorted-wave impulse approximation (DWIA) as well as in the distorted-wave Born approximation (DWBA).     

Elastic and inelastic scattering of identical heavy ions

The elastic and inelastic scattering of ¹²C, ¹²C, ²⁴Mg, ²⁴Mg, ²⁸Si, ²⁸Si was studied at bombarding energies E_c.m. = 5–18.8, 20–33, 29–36 MeV, respectively. The experimental arrangement includes two position sensitive detectors covering the angular ranges from O₁₂₄ = 20°–70°. The results are compared to calculations within the framework of the diffraction and optical model. A phase shift analysis is performed for the elastic scattering data of the ¹²C+¹²C system. It is shown that a shallow nuclei potential in needed to reproduce the ²⁸Si+²⁸Si results and that the ¹²C, ¹²C scattering shows evidence of resonance formation in the elastic channel.