Differential cross sections for elastic scattering and positronium formation for positron collisions with Ne,Ar, Kr and Xe

Differential cross sections for elastic scattering and Ps(1s) formation are calculated in the truncated coupled-static (TCS) approximation. Comparison is made with the elastic scattering measurements of Dou et al. on Ar and Kr. There is no support from the TCS approximation for the view that structure seen in the experimental results for Ar in the energy range 55–60 eV may be due to a resonance associated with coupling to the positronium formation channel. Rather, we believe that Dou et al. are right in correlating this feature with the maximum in the ionization cross section. In the experiment on Kr structures are observed at 25 and 200 eV. It is tentatively suggested that the structure at 200 eV may be the resonance seen in the TCS calculation at 100 eV, but modified by polarization and absorption effects. It is also suggested that the feature at 25 eV could be associated with coupling to excited states of positronium. The TCS results for the Xe target predict some very pronounced behaviour which would be worth experimental investigation. TCS differential cross sections for Ps(1s) formation by capture of an electron from the outer p-shell of the atom are presented for impact energies up to 75 eV. A noticeable property of these cross sections is that they do not usually peak at the forward direction; this is consistent with an experimental observation by Laricchia et al. on He and Ar targets. The importance of also looking at electron capture from inner shells is emphasized and illustrated by the cross section for electron capture from the 3s shell of Ar.     

The excitation temperature functions of some spectrum lines of He,Ne, Ar,Kr and Xe

The excitation temperature functions of 19 spectrum lines of 5 rare gases He, Ne, Ar, Kr, Xe have been calculated according to the method given by Fowler and Milne. The results make it possible to determine the radial plasma temperature distribution in the range of temperatures of 1.4 × 10⁴°K to 14 × 10⁴°K. Some examples are given for the determination of the plasma temperature distribution in space and time by using the Ar ecxitation temperature functions calculated.     

He,Ne,Ar,Kr和Xe原子电子的动量密度分布研究

对He,Ne,Ar,Kr和Xe原子体系中电子在动量空间的性质进行了系统的理论计算研究.采用自洽场HFR方法计算了坐标空间He,Ne,Kr和Xe原子体系单电子径向波函数,动量空间的单电子波函数由坐标空间原子体系单电子径向波函数通过运用傅立叶变换计算得到.在冲量近似条件下,进一步计算研究了这些原子的单电子动量密度分布和原子体系总的Compton轮廓.计算结果与已有的实验实验值和其他文献的理论计算结果比较表明,本文计算的结果是准确的.     

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.     

Differential cross sections for ionization of laser-aligned atoms by electron impact

The first experimental data are given for (e,2e) ionization from laser-aligned atoms. A linearly polarized laser excited Mg atoms to the 31P? state prior to ionization by low energy electrons. The scattered and ejected electrons were detected in coincidence and the differential cross section determined for a range of alignment angles. An asymmetric coplanar geometry was used, with one electron fixed and the other detected at different angles. The data are compared to that from the spherically symmetric 31S? state. Significant differences are found, in both magnitude and angular distribution.     

Geometrical model approximation for ionization cross sections of atoms and ions in ion-atom collisions

The applicability of the geometrical model (GM) proposed in [14, 15] to calculate the ionization probability and cross section of atoms and ions during collisions with ions, including structural ions, was studied at high velocities of partners. The GM represents a version of the classical impulse approximation. It was shown that the GM in all cases under consideration allows estimation of the ionization probability and total corss section of an atom or an ion during collisions with ions with deviations of no more than 50% from the results of the classical Monte Carlo method. GM calculations are rather simple in computation respect and limit the ionization probability by unity at arbitrary impact parameters.     

Plane wave born cross sections including exchange forK-shell ionization of light atoms

Cross sections forK-shell ionization by electron impact have been calculated in plane wave Born approximation (PWBA) including outer screening with allowance for electron exchange in Ochkur approximation. The results agree reasonably with available experimental data.     

Differential cross sections for charge transfer in collisions of He+, Ne+ and Ar+ with Kr

Differential charge transfer cross sections for collisions of He⁺, Ne⁺ and Ar⁺ with Kr were measured at collision energies below 500 eV. A remarkable fraction of these collisions (2–30 %) occurs with large momentum transfer and small impact parameters. These close collisions lead to an excitation of the product particles, the measured reaction channels are strongly endothermic. In the system Ar⁺+Kr one reaction channel may be described in terms of a curve crossing.     

Empirical model for electron impact ionization cross sections of neutral atoms

A simple empirical formula is proposed for the rapid calculation of electron impact total ionization cross sections both for the open- and closed-shell neutral atoms considered in the range 1≤ Z≤92 and the incident electron energies from threshold to about 10⁴ eV. The results of the present analysis are compared with the available experimental and theoretical data. The proposed model provides a fast method for calculating fairly accurate electron impact total ionization cross sections of atoms. This model may be a prudent choice, for the practitioners in the field of applied sciences e.g. in plasma modeling, due to its simple inherent structure.     

Calculations of total ionization cross sections for halogen compounds on electron impact from threshold to 2 keV

Calculation for electron impact total ionization cross sections on halogen compounds (BF, SiF, BCl, SiCl) are performed employing Spherical Complex Optical Potential and Complex Optical Potential — ionization contribution (CSP-ic) formalisms. In this article we are presenting data for energies ranging from above threshold to 2000 eV. Our results are compared with available experimental and theoretical data wherever available. It is found that the present result gives a better account of the ionization cross sections.     

Atomic properties for Ne,Ar, Kr from an optimised potential model for atoms

A variationally optimised effective atomic central potential has been used to calculate atomic form factors, 〈r²〉, ionization potentials, and dipole polarizabilities for Ne, Ar and Kr. The predictions agree very closely with Hartree-Fock results.     

Quenching cross-sections of metastable Ar,Kr and Xe atoms by halogen molecules

Summary The quenching of metastable Ar, Kr and Xe atoms by halogen molecules via an electron jump mechanism is examined by using the multiple curve-crossing formalism of Bauer, Fisher and Gilmore. Cross-sections for the quenching process are calculated which are found in good agreement with experiment. Finally, the model presented here is compared with other quenching mechanisms.

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Riassunto Si esamina la tempra di atomi metastabili di Ar, Kr, e Xe mediante molecole di alogeni attraverso un meccanismo di salto di elettroni, usando il meccanismo d'incrocio multiplo di curve di Bauer, Fisher e Gilmore. Si calcolano le sezioni d'urto per il processo di tempra che appaiono in buon accordo coi dati sperimentali. Infine il modello qui presentato è confrontato con altri meccanismi di tempra.

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Резюме Используя формализм Бауэра, Фишера и Джилмора, исследуется гашение метастабильности атомов Ar, Kr и Xe молекулами галогенов через механизм электронного перескока. Вычисляются поперечные сечения для процесса гашения, которые согласуются с экспериментом. В заключение предложенная модель сравнивается с другими механизмами гашения.

     

Determination of three-photon ionization cross sections of xenon atoms from comparison with electron ionization

Multiphoton and electron-impact ionization of a gas-dynamic beam of xenon atoms are compared in order to determine the effective multiphoton ionization cross sections. The three-photon ionization cross section of the xenon atom is determined.     

Double-hump resonance structure of the cross sections for electron impact ionization of Ar5+

Configuration-average distorted-wave calculations are carried out for electron-impact ionization of Ar5+. Both direct ionization and the indirect excitation autoionization processes are included in our calculations. Our theoretical values are in quite reasonable agreement with the experimental data. The indirect processes contribute up to 50% to the total ionization cross sections. The possible origin of double-hump resonance structure of the cross sections is demonstrated and the contributions of metastable states are also taken into account.     

Logarithmically accurate total cross sections of fast electron scattering by atoms

A simple analytical formula for the total integrated cross section of fast electron scattering by atoms is obtained. This formula, being logarithmically accurate, is derived from the approximate rule of sum that does not take into account exchange effects in the atomic wave function (Hartree approximation). It is shown that exchange effects can be neglected in that scattered electron energy range where the first Born approximation is valid. The results of calculation for He, Ne, and Ar atoms agree well with experimental data.     

Formation and migration properties of the rare gases He,Ne, Ar,Kr, and Xe in nickel

The energies of formation and migration of various rare gas-point defect complexes in an f.c.c. nickel lattice have been calculated for He, Ne, Ar, Kr, and Xe. Formation energies of rare gas atoms at interstitial sites are compared with those in substitutional sites. Binding energies are presented for self-interstitials and vacancies trapped to the various rare gas substitutionals. We also present migration energies and migration paths for various rare gas interstitials and substitutionals with and without trapped vacancies and self-interstitials. The migration energies are compared with the breakup energies for the corresponding complexes. We find that divacancy-rare gas complexes are rather stable and will migrate at relatively low energies compared to other substitutional rare gas migration processes.     

Al,Ti,Cu,Mo原子的K壳层电离截面的理论计算

 电子离子碰撞过程是模拟激光等离子体的超热电子的能谱和产额的主要过程之一。基于相对论性的电子离子碰撞的K壳层的电离截面理论,计算了Al,Ti,Cu,Mo原子的K壳层的电子离子碰撞截面,结果和最近的文献实验数值和其它理论数值进行了比较,计算结果可用来模拟激光等离子体的超热电子能谱和产额。