Line scattering images on crystals of NaCl with nickel. II

Using the ifrin integro-differential equation an expression was found for the intensity of the diffracted radiation of a prism, the conditions were found for the formation of a line scattering image, the shape of the line scattering image of a rod in different positions with respect to the primary beam was determined and it was proved that the form of this scattering image does not depend either on the refractive index of the rod or on the wave-length of light of the primary ray. A comparison with the experimentally measured line images showed that in an NaCl crystal with nickel added there are rod-like formations (probably formed by nickel chloride), their principal dimension being oriented uniformly in all equivalent directions (110) of the lattice of the basic substance. The minimum length of the rods was estimated at above 20 000 å and the maximum transversal dimension of the rod below 2500 å.The authors thank M. lová for carefully performing the measurements and A. Línek for valuable remarks.     

Optical gain measurements in doped alkali-halides

In order to verify the possibility of obtaining laser action in doped alkali-halides crystals, optical amplification measurements have been performed by the amplified spontaneous emission (ASE) technique. Results obtained in CsI : In(Tl) crystal are reported and discussed.     

Effect of external stresses on the optical absorption ofU 2-centers in alkali-halides

An electric dipole transition model is used to investigate the influence of applied external stresses on the optical absorptionband of U₂-centers in alkali-halides. An analysis of the effect can be made by the method of moments. The results are similar to what happens in the case of aF-center, except that the Γ₄-mode must also be taken into account.     

Absorption spectra of excitons in alkali-halides in the vacuum-ultra-violet region

On the basis of the localized excitation model, the spectra of K⁺ - 3p electron excitation in potassium halides are studied theoretically by using methods of the ligand field theory and a good agreement with the experiment is obtained. Some discussions are given on the applicability of the Frenkel exciton model to the VUV spectra of other alkali halides.     

Line shape and moment analysis in depolarized induced light scattering

We compare the two methods of deriving interaction-induced pair polarizabilities from collision-induced, depolarized spectra, namely classical line shape and moment analysis. We discuss their limitations and show that the joint use of line shape and moment analysis leads to the determination of an empirical pair polarizability anisotropy model which has maximal consistency with the available experimental results. We have applied the combined method to the pair spectrum of argon at room temperature (298 K) as an example.     

Impact of dynamical scattering on quantitative contrast for aberration-corrected transmission electron microscope images

Aberration-corrected transmission electron microscope images taken under optimum-defocus conditions or processed offline can correctly reflect the projected crystal structure with atomic resolution. However, dynamical scattering, which will seriously influence image contrast, is still unavoidable. Here, the multislice image simulation approach was used to quantify the impact of dynamical scattering on the contrast of aberration-corrected images for a 3C-SiC specimen with changes in atomic occupancy and thickness. Optimum-defocus images with different spherical aberration (C_S) coefficients, and structure images restored by deconvolution processing, were studied. The results show that atomic-column positions and the atomic occupancy for SiC ‘dumbbells’ can be determined by analysis of image contrast profiles only below a certain thickness limit. This limit is larger for optimum-defocus and restored structure images with negative C_S coefficient than those with positive C_S coefficient. The image contrast of C (or Si) atomic columns with specific atomic occupancy changes differently with increasing crystal thickness. Furthermore, contrast peaks for C atomic columns overlapping with neighboring peaks of Si atomic columns with varied Si atomic occupancy, which is enhanced with increasing crystal thickness, can be neglected in restored structure images, but the effect is substantial in optimum-defocus images.     

Six-quark admixtures in two-nucleon systems

The coupled-channel model for multiquark and nucleon-nucleon channels in nuclei is developed. The quark-quark forces and the nucleon-nucleon phenomenological interaction are used for calculations. As an example, estimations of the probability for the six-quark admixture in a deuteron and of the widths of the six-quark resonances in the nucleon-nucleon scattering were done. These values are discussed and compared with those obtained from the corresponding experimental data on the ed-elastic scattering, cumulative processes and NN-scattering.     

Line broadening effect in the rayleigh scattering of Mössbauer radiation on single crystals

BaTiO₃ and Ba_0.54Sr_0.46Nb₂O₆ single crystals were studied near the ferroelectric phase transitions by Mössbauer diffraction. It is shown that in these samples slow (5–10 MHz) relaxation motions occur leading to a remarkable broadening in the Mössbauer spectra of the scattered radiation.     

基于高光谱成像的苹果多品质参数同时检测

利用高光谱空间散射曲线的3个洛伦兹拟合参数对苹果的品质(硬度、可溶性固溶物含量)进行同时检测。采用偏最小二乘,逐步多元线性回归和BP神经网络3种方法,对归一化处理和未归一化处理的3个洛伦兹参数组合分别建立苹果品质的预测模型。结果表明:采用偏最小二乘法对未归一化处理参数的组合建立硬度的预测模型其预测结果最好,校正组相关系数Rc=0.93,校正标准差SEC=0.56,验证组相关系数Rv=0.84,验证标准差SEV=0.94。采用偏最小二乘法对归一化处理参数的组合建立可溶性固形物的预测模型其预测结果最好,Rc=0.95,SEC=0.29,Rv=0.83,SEV=0.63。研究结果表明:利用高光谱空间散射曲线的多拟合参数组合可以同时检测苹果的多品质参数。     

Line shape of the collision-induced scattering in CF4

Results on the spectral shape of the collision-induced scattering (CIS) of CF₄ gas are obtained for densities up to 270 amagats (296 K). For low frequencies they are compared with dipole-induced dipole theory; for high frequencies a short distance-induced binary collision model describes the observed spectral shape fairly well.     

Acoustic quasi-holographic images of scattering by vertical cylinders from one-dimensional bistatic scans

When synthetic aperture sonar (SAS) is used to image elastic targets in water, subtle features can be present in the images associated with the dynamical response of the target being viewed. In an effort to improve the understanding of such responses, as well as to explore alternative image processing methods, a laboratory-based system was developed in which targets were illuminated by a transient acoustic source, and bistatic responses were recorded by scanning a hydrophone along a rail system. Images were constructed using a relatively conventional bistatic SAS algorithm and were compared with images based on supersonic holography. The holographic method is a simplification of one previously used to view the time evolution of a target's response [Hefner and Marston, ARLO 2, 55-60 (2001)]. In the holographic method, the space-time evolution of the scattering was used to construct a two-dimensional image with cross range and time as coordinates. Various features for vertically hung cylindrical targets were interpreted using high frequency ray theory. This includes contributions from guided surface elastic waves, as well as transmitted-wave features and specular reflection.     

Line shape broadening in surface diffusion of interacting adsorbates with quasielastic he atom scattering

The experimental line shape broadening observed in adsorbate diffusion on metal surfaces with increasing coverage is usually related to the nature of the adsorbate-adsorbate interaction. Here we show that this broadening can also be understood in terms of a fully stochastic model just considering two noise sources: (i) a Gaussian white noise accounting for the surface friction, and (ii) a shot noise replacing the physical adsorbate-adsorbate interaction potential. Furthermore, contrary to what could be expected, for relatively weak adsorbate-substrate interactions the opposite effect is predicted: line shapes get narrower with increasing coverage.     

Single-particle proton admixtures in core-excited states of Bi

At least 18 states up to 3.5 MeV of excitation have been observed in the ²⁰⁶Pb(³He, d)²⁰⁷Bi reaction at 35 MeV. The experimental spectrum and spectroscopic factors are in fair agreement with the predictions of the weak-coupling model up to an excitation energy of 2.5 MeV.     

Line shapes and threshold resonances for the scattering of waves from surfaces

An analytical study of threshold resonances in scattering of scalar waves from periodic surfaces is presented. Resonances are found with a variety of line shapes which provide characteristic information on the surface potential. The analytical predictions on line shapes are supported numerically. These resonances should be observed in atom-surface scattering and in scattering of light from large-amplitude gratings. We think that these resonances may be important for the field enhancement on surfaces.     

Multiple scattering calculations of step contrast in REM images of the Si(001) surface

Simulations of reflection electron microscopy (REM) images of both monolayer and bilayer steps on the bulk-terminated Si(001) surface, for the case when the primary electron beam azimuth is directed parallel to the line of the step, are presented. The simulations employ our previously reported theory of REM image formation which uses a 2D Bloch wave formulation of dynamical (multiple scattering) elastic RHEED theory to calculate diffracted amplitudes propagating from the surface. The only step contrast mechanism considered here is phase contrast and this is sufficient to produce the characteristic “black-white” appearance observed experimentally. Defocusing of the simulated images is also discussed.