锂原子光电离截面的无穷阶计算

利用多体微扰理论,把基态锂原子K和L壳层电子的光电离过程中的电子相关效应计算到了无穷阶。用Feynman图技术讨论了基态关联效应和混相近似效应,并计算了与无穷阶末态关联的耦合效应。计算结果与实验和其他理论结果吻合得很好。     

Fits to new calculations of photoionization cross sections for low-Z elements

Analytical approximations to results of new calculations of partial (i.e. by subshell) photoionization cross sections of elements (2 < Z < 30, Z = 36) are presented which cover the photon energy range from near threshold to 300 keV. The computer program developed by Brysk and Zerby, which is based on the single-electron model and uses screened self-consistent field and Dirac-Slater wave function data furnished by Cromer, Waber and Liberman, was used. Sufficient multipoles were included to calculate the partial cross sections within a few per cent, on the assumed model. Results for several elements are compared with other calculations and measurements of total photoionization cross sections. The results are presented in a form most convenient for calculations of opacities of hot gases.     

Sm和U原子光电离截面的模型势计算

本文给出了使用四种不同形式的势对Sm基态光学电子所属壳层光电离截面计算的结果,同时给出了U原子三个激发态参量形式的极化修正模型势光电离截面的计算结果.我们的结果与其他作者使用相同形式的势计算的结果较好地符合.使用参数形式的极化模型势计算光电离截面是一种有效的方法.     

Close coupling calculations for excitation partial cross sections in Ne--HF collisions

This paper reports that an exact quantum close coupling calculation is carried out for rotational excitation in Ne HF collisions on the available anisotropic potential. Partial cross sections are obtained separately at the incident energies of 48.35, 75, 120 and 150meV. The reliability of the results is demonstrated by comparison with previously published theoretical findings. Based on the calculations, the effect of the potential energy surface on the excitation partial cross sections is discussed in detail.     

Partial photoionization cross sections of C60 and C70: A gas versus adsorbed phase comparison

We have performed high resolution measurements of the photoelectrons emitted from the valence shell of C₆₀ and C₇₀, in the gas phase and adsorbed phase on a metal surface, in order to derive branching ratios and the partial photoionization cross sections of the two highest occupied molecular orbitals, HOMO and HOMO-1. The comparison between the gas phase and the adsorbed phase shows an interesting and unexpected difference that can be attributed to a small orbital shift in solid C₇₀. Density Functional Theory calculations within the Local Density Approximation (LDA) show good agreement for both data sets and give a plausible explanation for the observed difference.     

Optical corrections in measurements of photoionization cross sections from solids in the soft X-ray range

We present measurements of photoelectron flux from the 4d band of Pd in the photon energy range 70–200eV. A comparison between measurements at different light incidence angles demonstrates the effect of the optical corrections (reflectivity and refraction) needed in the measurement of photoionization cross sections. It is shown that simple model calculations account satisfactorily for this effect.     

Coupled-static calculations of the partial and total cross sections of positron-lithium inelastic scattering

The inelastic scattering of positrons by lithium atoms has been investigated in details using a combination of the frozen-core and coupled-static approximations. The ground state of the target has been described by Walters' wave functions. The partial cross sections corresponding to 8 values of the total angular momentuml (0l7) are determined for 21 values of the incident energy lying between 0·1 and 1000 eV. Our results illustrate the stability of the iterative numerical technique employed. They demonstrate the role played by each partial wave in the total cross sections and emphasize the argument that the effect of positronium formation on the total collisional cross sections diminishes when the incident energy is larger than 30 eV.     

Dirac R-matrix calculations of photoionization cross sections of Ni XII and atomic structure data of Ni XIII

We performed R-matrix calculations for photoionization cross sections of the two ground state configuration 3s²3p⁵ (²P^o_3/2,1/2) levels and 12 excited states of Ni XII using relativistic Dirac Atomic R-matrix Codes (DARC) across the photon energy range between the ionizations thresholds of the corresponding states and well above the thresholds of the last level of the Ni XIII target ion. Generally, a good agreement is obtained between our results and the earlier theoretical photoionization cross sections. Moreover, we have used two independent fully relativistic GRASP and FAC codes to calculate fine-structure energy levels, wavelengths, oscillator strengths, transitions rates among the lowest 48 levels belonging to the configuration (3s²3p⁴, 3s3p⁵, 3p⁶, 3s²3p³3d) in Ni XIII. Additionally, radiative lifetimes of all the excited states of Ni XIII are presented. Our results of the atomic structure of Ni XIII show good agreement with other theoretical and experimental results available in the literature. A good agreement is found between our calculated lifetimes and the experimental ones. Our present results are useful for plasma diagnostic of fusion and astrophysical plasmas.     

Orthogonalized-plane-wave approximation in the calculation of photoionization cross sections of molecules

The physical bases of the OPW approximation in the calculation of molecular photoionization cross sections are considered in terms of the scattering theory, and the ways of improving the calculation within the framework of OPW approximation are discussed.Numerical calculations are done on several molecules by the ordinary OPW method and by its modifications using the bound orbitals obtained by ab initio SCFMO calculations with gaussian basis set.     

Calculation of the photoionization with deexcitation cross sections of He and helium-like ions

We discuss the results of the calculation of the photoionization with deexcitation of excited He and helium-like ions Li⁺ and B³⁺ at high but nonrelativistic photon energies θ. Several lower ¹ S and ³ S states are considered. We present and analyze the ratios R _d ⁺ * of the cross sections of photoionization with deexcitation, σ _(d) ⁺ *(θ), and of the photoionization with excitation, σ⁺*(θ). The dependence of R _d ⁺ * on the excitation of the target object and the charge of its nucleus is presented. In addition to theoretical interest, the results obtained can be verified using long-lived excited states such as 2³ S of He. The text was submitted by authors in English.     

高密度体系光电离截面新表达式的应用

利用实验光谱学的Beer Lambert定律和介质中的麦克斯韦方程组，建立了精确的光吸收（光电离）截面表达式，并通过一个随体系粒子数密度和宏观复介电常数而变化的变换函数，将严格截面公式与Fano和Cooper 1968年建立的理想气体的光电离截面公式直接联系起来.建议：1)当知道某密度下正确的体系宏观复介电常数β,γ时，可直接由严格表达式求得高密度下非理想状态的正确光电离截面；2)或当知道该体系的粒子微观极化率η,ζ和其理想气体的精确截面时，用上述变换公式间接求得其他密度时的光电离截面.对氩原子和氙原子的应用表明：当缺乏β,γ时，可由某一合理的宏观电极化率物理（例如克劳修斯-莫索缔）模型来计算β,γ，从而获得高密度体系的截面.这样获得的结果符合被散射物质的光电离（光吸收）截面随体系粒子数密度增大而增加的客观散射现象.而且，考虑了高密度真实体系中粒子间相互作用的宏观电极化率模型越正确，如此求得的散射截面的误差就越小. 关键词： 光电离截面 光吸收截面 介电常数 极化率     

真实体系光电离截面共振结构的理论研究

利用我们提出的普遍适用的精确光电离截面公式和介电影响函数研究了原子光电离共振结构受粒子数密度影响的效应.结果表明用新的光电离截面公式可以直接处理宏观环境对截面的影响,明显地优于孤立原子光电离截面公式.     

Absolute photoionization cross sections with ultra-high energy resolution for Ar, Kr, Xe and N2 in inner-shell ionization regions

The high-resolution absolute photoionization cross sections for Ar, Kr, Xe and N₂ in the inner-shell ionization region have been measured using a multi-electrode ion chamber and monochromatized synchrotron radiation. The energy ranges of the incident photons for the target gases were as follows: Ar: 242–252 eV (2p Rydberg excitation), Kr: 1650–1770 eV (near the 2p ionization thresholds), Xe: 665–720 eV (near the 3d ionization thresholds) and 880–1010 eV (near the 3p ionization thresholds), N₂: 400–425 eV (N 1s excitation and ionization). It is the first time to measure the absolute ionization cross sections of Ar, Kr, Xe and N₂ over the present energy ranges with the energy resolution of over 10,000. The natural lifetime widths of , , and resonances for Ar, resonance for Xe, and resonance for N₂ have been obtained based on the cross sections determined. The ionization energies into the Ar⁺ (), Ar⁺ () and Xe⁺ () ionic states are also determined using the Rydberg formula.     

A comparison of absolute cross sections for electro- and photo-induced reactions

Absolute cross sections for electron and positron induced reactions on¹²C,⁶³Cu and¹⁰⁷Ag are compared with cross sections for the corresponding photo-induced reactions in order to test DWBA calculations of the virtual photon spectra. A good agreement is found between the experimental cross sections for the electrodisintegration and those calculated with DWBA spectra and photonuclear cross sections.     

Relative measurements of photofission cross sections with the use of a bremsstrahlung spectrum

This survey is devoted to the investigation of fission probability by measuring photofission yields using a bremsstrahlung spectrum of the microtron with the relative measurement method in the region of energies from the threshold to the upper boundary of the fissility plateau (E < 11 MeV). The results were obtained using a unique technique for nineteen nuclei from ²³²Th to ²⁴⁹Cf. For some nuclei in the threshold energy region, detailed measurements were performed which provided the possibility of observation of new resonances in the photofission cross section. The observed resonance effects are discussed. For ²³⁴U and ^{238, 240, 242}Pu, theoretical analysis was performed to obtain the fission barrier parameters for fission channels with particular quantum states. Data of other measurements of photofission cross sections are given, along with the results obtained in the surveyed series of measurements. The data obtained using the relative measurement method is compared with data for other reactions that result in fission of the nuclei under study.