Differential and Integral Cross Sections for Electron Impact Excitation of Lithium

The differential and integral cross sections for electron impact excitation of lithium from the ground state 1s(2)2s to excited states 1s(2)2p, 1s(2)3l (l = s,p,d) and 1s(2)4l (l = s,p,d,f) at incident energies ranging from 5 eV to 25 eV are calculated by using a full relativistic distorted wave method. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbitals are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. A part of the cross sections are compared with the available experimental data and with the previous theoretical values. It is found that, for the integral cross sections, the present calculations are in good agreement with the time-independent distorted wave method calculation, for differential cross sections, our results agree with the experimental data very well.

X-ray spectrum emitted by the impact of Xe-129(q+) on Mo surface

We studied the characteristic X-ray spectra produced by the interaction of highly charged ions of X-129(q+) (q =25, 26, 27) with surface of metallic Mo. The experimental result shows that highly charged ions can excite the characteristic X-ray spectra of L-shell of Mo when the beam' s intensity is not more than 120 nA. The X-ray yield of single ion reaches a quantitative level of 10(-8) and increases with the increment of the ion' s kinetic energy and ionic charge (potential energy). By measuring the X-ray spectra of Mo-L alpha(1) the M-level lifetime of Mo atom is estimated by using Heisenberg uncertainty relation.

~(129)Xe~(q+)激发Mo表面产生的X射线谱；X-ray spectrum emitted by the impact of ~(129)Xe~(q+) on Mo surface

研究了高电荷态离子129Xeq+(q=25,26,27)入射金属Mo表面产生的特征X射线谱.实验结果表明,在束流强度小于120nA条件下,高电荷态离子129Xeq+可以激发Mo的L壳层特征X射线谱.单离子X射线相对产额可达10-8量级,特征X射线的相对产额随入射离子的动能和电荷态(势能)的增加而增加.通过Mo原子的Lα1特征X射线谱,利用Heisenberg不确定关系对Mo原子的第M能级寿命进行了估算.

NUCLEON-NUCLEON CROSS SECTIONS IN ISOSPIN ASYMMETRIC NUCLEAR MATTER

The in medium nucleon-nucleon (N N) cross sections in isospin asymmetric nuclear matter at various densities are investigated in the frame work of Brueckner-Hartree-Fock theory with the Bonn B two-body nucleon-nucleon inter action supplemented with a new version microscopic three-body force (TBF). The TBF depresses the amplitude of cross sections at high density region. At low densities, the proton-proton and neutron-neutron cross sections decrease while the proton-neutron one increases as the asymmetry increases. But the sensitivity of the N N cross sections to the isospin a symmetry are reduced with the increasing density.

Studies of K-shell x-ray energy shifts induced by MeV/u heavy ions

This paper reports that the K x-ray spectra of the thin target 47Ag, 48Cd, 49In and 50Sn were measured by an HPGe semi-conductor detector in collisions with 84.5 MeV 6C4+ ions. Our experiment revealed the Kα x-ray energy shifts were not obvious and the Kβ1 x-ray energy shifts were about 90∼110 eV. The simple model of Burch et al has been previously used to calculate the K x-ray energy shifts due to an additional vacancy in 2p orbit. The present work extends the model of Burch to calculate the x-ray energy shifts of multiple ionized atoms induced by heavy ions with kinetic energy of MeV/u. In addition to our experimental results, many other experimental results are compared with the calculated values by using the model.

Investigation of Degradation Behavior of Polymer on Surface of Film Due to the Existence of Monochromatic X-ray

Degradation and its temperature dependence of poly(methyl methacrylate) (PMMA) in the blend film of PMMA/SAN were investigated via ire-situ X-ray photoelectron spectroscopy(XPS). The results show that thermal degradation of PMMA takes place at 185, 130, 80 degrees C and even room temperature due to the existence of monochromatic X-ray. Furthermore, the degradation rate depends crucially on the experiment temperature.

Effect of annealing on the deformation mechanism of a styrene/n-butyl acrylate copolymer latex film investigated by synchrotron small-angle X-ray scattering

The deformation mechanism of a styrene/n-butyl acrylate copolymer latex film subjected to uniaxial tensile stress was studied by small-angle X-ray scattering. The influence of annealing at 23, 60, 80, and 100 degrees C for 4 h on microscopic deformation processes was elucidated. It was demonstrated that the microscopic deformation mechanism of the latex films transformed gradually from nonaffine deformation behavior to affine deformation behavior with increasing annealing temperature.

Preparation of Hollow Carbon and Silicon Carbide Fibers with Different Cross-Sections by using Electrospun Fibers as Templates

Hollow carbon nanofibers with circular and rectangular opening were prepared by using electrospun silica fibers as templates. Silica fibers were synthesized by electrospinning, and they were coated with a carbon layer formed by thermal decomposition and carbonization of polystyrene under a nitrogen atmosphere. Hollow carbon nanofibers with circular and rectangular openings were then obtained after the silica core was etched by hydrofluoric acid. The carbon nanofibers with different morphologies also could be used as templates to fabricate silicon carbide fibers. The silicon carbide fibers with circular and rectangular openings could be obtained by using hollow carbon nanofibers and carbon belts as templates, respectively.

Structural evolution of tensile deformed high-density polyethylene at elevated temperatures: Scanning synchrotron small- and wide-angle X-ray scattering studies

The structural evolution of an ice-quenched high-density polyethylene (HDPE) subjected to uniaxial tensile deformation at elevated temperatures was examined as a function of the imposed strains by means of combined synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. The data show that when stretching an isotropic sample with the spherulitic structure, intralamellar slipping of crystalline blocks was activated at small deformations, followed by a stress-induced fragmentation and recrystallization process yielding lamellar crystallites with their normal parallel to the stretching direction. Stretching of an isothermally crystallized HDPE sample at 120 degrees C exhibited changes of the SAXS diagram with strain similar to that observed for quenched HDPE elongated at room temperature, implying that the thermal stability of the crystal blocks composing the lamellae is only dependent on the crystallization temperature.

DEFORMATION OF SOFT COLLOIDAL CRYSTALLINE STRUCTURE - THEORETICAL CONSIDERATIONS AND EXPERIMENTAL EVIDENCES BY SYNCHROTRON SMALL-ANGLE X-RAY SCATTERING ON TENSILE STRETCHED POLYMERIC LATEX FILM

Films obtained via drying a polymeric latex dispersion are normally colloidal crystalline where latex particles are packed into a face centered cubic (fcc) structure. Different from conventional atomic crystallites or hard sphere colloidal crystallites, the crystalline structure of these films is normally deformable due to the low glass transition temperature of the latex particles. Upon tensile deformation, depending on the drawing direction with respect to the normal of specific crystallographic plane, one observes different crystalline structural changes. Three typical situations where crystallographic c-axis, body diagonal or face diagonal of the fcc structure of the colloidal crystallites being parallel to the stretching direction were investigated.

Uniaxial deformation of overstretched polyethylene: In-situ synchrotron small angle X-ray scattering study

Synchrotron small angle X-ray scattering was used to study the deformation mechanism of high-density polyethylene that was stretched beyond the natural draw ratio. New insight into the cooperative deformational behavior being mediated via slippage of micro-fibrils was gained. The scattering data confirm on the one hand the model proposed by Peterlin on the static structure of oriented polyethylene being composed of oriented fibrils, which are built by bundles of micro-fibrils. On the other hand it was found that deformation is mediated by the slippage of the micro-fibrils and not the slippage of the fibrils. In the micro-fibrils, the polymer chains are highly oriented both in the crystalline and in the amorphous regions. When stretching beyond the natural draw ratio mainly slippage of micro-fibrils past each other takes place. The thickness of the interlamellar amorphous layers increases only slightly. The coupling force between micro-fibrils increases during stretching due to inter-microfibrillar polymer segments being stretched taut thus increasingly impeding further sliding of the micro-fibrils leading finally to slippage of the fibrils.

Structural evolution of tensile-deformed high-density polyethylene during annealing: Scanning synchrotron small-angle X-ray scattering study

The structural evolution of high-density polyethylene subjected to uniaxial tensile deformation was investigated as a function of strain and after annealing at different temperatures using a scanning synchrotron small-angle X-ray scattering (SAXS) technique. The results confirm that in the course of tensile deformation intralamellar block slips were activated at small deformations followed by a stress-induced fragmentation and recrystallization process yielding thinner lamellae with their normal parallel to the stretching direction. The original sheared lamellae underwent severe internal deformation so that they were even less stable than the newly developed thinner lamellae. Accordingly, annealing results in a melting of the original crystallites even at moderate strains where the stress-induced fragmentation and recrystallization just sets in and generates a distinctly different form of lamellar stacks aligned along the drawing direction. It was found that the lamellae newly formed during stretching at moderate strains remain stable at lower temperature. Only at a very high annealing temperature of 120 degrees C can they be melted, leading to an isotropic distribution of the lamellar structure.