Theoretical study of photoionization of the isoelectronic sequence Rb<Superscript>+</Superscript>, Sr<Superscript>2+</Superscript>, and Y<Superscript>3+</Superscript>

The photoionization cross sections for the 4p shell of ions of the Kr isoelectronic sequence Rb⁺, Sr²⁺, and Y³⁺ are calculated. The configuration interaction theory and the perturbation theory are used to describe the many-electron effects. The relativistic effects are taken into account in the Pauli-Fock approximation. The calculated resonance structure of photoionization cross sections for the 4p shell in the region below the 4s threshold associated with the autoionization of the 4s-np singly excited states and the 4p4p-nln′l′ doubly excited states reproduces the results of recent measurements of total photoabsorption cross sections for the Rb⁺, Sr²⁺, and Y³⁺ ions. It is found that, as the nuclear charge in the isoelectronic sequence increases, the ratio between the direct and correlation parts of amplitudes of the 4s-(n/?)p transition changes and, as the consequence, the minimum of the photoionization cross section of the 4s shell shifts from the continuous spectrum to the region of states of discrete spectrum. This accounts for the strong changes in the shape of the 4s-np resonances in the photoionization cross sections for the 4p shell of Rb⁺, Sr²⁺, and Y³⁺, as well as the distinction between the shapes of the 4s-6p _1/2 mirror resonance in the partial 4p _1/2 and 4p _3/2 photoionization cross sections for the Y³⁺ ion which do not suppress each other in the total photoionization cross section, as is the case for similar resonances in Rb⁺ and Sr²⁺.     

Theoretical study of charge-exchange and excitation processes in collisions of He<Superscript>+</Superscript> ions with C<Superscript>5+</Superscript>, N<Superscript>6+</Superscript>, and O<Superscript>7+</Superscript> hydrogen-like ions

Data on the cross sections for single-electron charge exchange and excitation in collisions of He⁺ ions with C⁵⁺, N⁶⁺, and O⁷⁺ ions in the He⁺ ion energy range of 0.2–3.0 MeV are obtained for the first time. The cross sections for the single-electron charge transfer into the singlet and triplet 1snl states of C⁴⁺, N⁵⁺, and O⁶⁺ (2≤n≤5) ions and for the 1s → 2p _{0, ±1} electronic excitation of He⁺(1s) ions are calculated. The calculations were performed by solving close-coupling equations on the basis of ten two-electron quasi-molecular states.     

Multiple ionization of neon 2s- and 2p-electrons induced by ion atom collisions

Absolute cross sections for production of the 1s ²2s2p ⁵ and 1s ²2s ⁰2p ⁶ configurations of neon in collisions of H⁺, He⁺, and Ne⁺ with Ne and He have been measured by observation of radiative transitions in the spectral range of the vacuum ultraviolet for energies between 50 keV and 1 MeV. Projectile and target emission have been separated. The dependence of the cross sections upon impact velocity is discussed and compared with theoretical calculations. The relative population of the¹ P ₁ and³ P _{2, 1, 0} and the³ P _{2, 1, 0} fine structure levels of the 1s ²2s2p ⁵ configuration is measured as function of impact velocity for the different projectile target combinations.     

Coulomb formation and evolution of muonium in vacuum

An exact calculation ofμ ⁺ e ^? Coulomb capture cross sections at various energies in the centre-of-mass system is reported. The population of 1s, 2s and 2p levels as function of the time elapsed after muonium formation is shown.     

类钠铜离子的激发自电离

在扭曲波库仑玻恩交换近似下计算了类钠铜离子２ｐ^６３ｓ＋ｅ^-→２ｐ⁵３ｓ３ｌ＋ｅ^-（ｌ＝０，１，２）的内壳层激发截面．结合单组态近似和组态相互作用两种情况下计算的自电离分支比，计算了上述组态的激发自电离截面．结果表明，在入射电子能量为１０９０ｅＶ时，组态相互作用使２ｐ⁵３ｓ３ｄ总的激发自电离截面增大至单组态近似的近两倍；而使２ｐ⁵３ｓ²组态的激发自电离截面减小为单组态近似的３６％；２ｐ⁵３ｓ３ｐ组态的激发自电离截面只是略有下降 关键词：     

Measurement of D0, D+, Ds+ and D*+ production in fixed target 920?GeV proton–nucleus collisions

The inclusive production cross sections of the charmed mesons D⁰,D⁺,D_s ⁺ and D^*+ have been measured in interactions of 920 GeV protons on C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of transverse momentum and Feynman’s x variable are given for the central rapidity region and for transverse momenta up to p_T=3.5 GeV/c. The atomic mass number dependence and the leading to non-leading particle production asymmetries are presented as well. PACS 13.85.Ni; 24.85.+p; 13.20.Fc     

Resonant charge transfer in slow H+-H collisions in the presence of a strong magnetic field

Resonant charge transfer in slow H⁺-H collisions proceeding in the presence of a strong, external magnetic field is investigated theoretically for field strengths of order 10⁵ T. Transfer probabilities and cross sections are calculated in a two-state approximation using exact molecular-orbital energies of the magnetically dressed H⁺₂ system. The field-affected cross sections are found to be substantially smaller than the field-free cross sections.     

Charge exchange and excitation cross sections at collisions of alpha particles with be-like impurity oxygen ions in a plasma

The charge exchange and excitation cross sections at collisions of alphas with O⁴⁺(1s ²2s ²) impurity atoms in a hot plasma for striking energies E _c varying from 20 keV to 2 MeV are determined for the first time. The cross sections are calculated using the method of close-coupling equations with 13 singlet four-electron quasi-molecular states taken as a basis. The partial cross sections of charge transfer to the 1s, 2s, and 2p states of a He⁺ ion and for O⁴⁺(1s ²2s ²) → O⁴⁺(1s ²2lnl’) (n = 2, 3) electronic excitation of an oxygen ion are found. The maximal value of the charge exchange total cross section roughly equals 2.2 × 10^?16 cm² at E _c ≈ 0.7 MeV. The excitation total cross section has a maximum of ≈ 7.7 × 10^?16 cm² at E _c ≈ 80 keV for single-electron excitation and ≈6.5 × 10^?16 cm² at E _c ≈ 0.7 MeV for two-electron excitation.     

Excitation of the 1s2- and 1s4-levels of neon and argon by He+-impact at energies between 100 keV and 1000 keV

The excitation of the 1s ₂- and 1s ₄-levels of neon and argon by He⁺-impact has been studied in the energy range of 100 keV to 1000 keV. The total emission cross sections for the 1s ₂ levels show pronounced maxima at about 350 keV impact energy, whereas the cross sections for the 1s ₄ levels increase with decreasing energy.     

Excitation of the 1s 2- and 1s 4-levels of neon and argon by He+-impact at energies between 100 keV and 1000 keV

The excitation of the 1s ₂- and 1s ₄-levels of neon and argon by He⁺-impact has been studied in the energy range of 100 keV to 1000 keV. The total emission cross sections for the 1s ₂ levels show pronounced maxima at about 350 keV impact energy, whereas the cross sections for the 1s ₄ levels increase with decreasing energy.     

Breit相互作用对类氦离子亚稳态1s2s 3S1电子碰撞激发截面的影响

利用新近发展的基于全相对论扭曲波方法研究电子-离子碰撞激发过程的计算程序,通过对Breit相互作用的考虑,计算了类氦等电子序列离子从亚稳态1s2s³S₁激发2s电子到n=2,3壳层的电子碰撞激发截面;研究了不同入射电子能量时Breit相互作用对碰撞激发截面的影响,进一步总结了沿等电子序列变化时,Breit相互作用对截面影响的一般规律.部分计算结果与实验结果进行了比较,得到了很好的一致性. 关键词： 全相对论扭曲波方法 Breit相互作用 电子碰撞激发截面     

Direct neutron scattering from 182W and 184W

Differential elastic and inelastic neutron scattering cross sections for ¹⁸²W and ¹⁸⁴W have been measured at incident energies 4.87 and 6.00 MeV. Cross sections for the first (0⁺, 2⁺, 4⁺, 6⁺), second (0⁺, 2⁺), and some higher excitations are presented. Angular distributions exhibit direct reaction characteristics, suggesting that compound cross sections for these states are small. This is supported by statistical-model calculations. Coupled-channel calculations of cross sections are made using a phenomenological deformed optical potential. Quadrupole and hexadecapole deformations have been searched to optimize fits. The necessity of introducing a β₆ deformation is investigated. Electric multipole transition matrix elements, used in the coupled-channel analysis, are obtained from the rotation-vibration model and the dynamic-deformation theory.     

Oscillator strengths of the vibrational and Rydberg transitions in the 1s absorption spectrum of a nitrogen molecule

Spectral dependences of the total absorption cross sections in the region of the 1s ionization threshold of molecular nitrogen are determined for the first time with a high energy resolution using synchrotron radiation from the Russian-German channel of the BESSY II electron storage ring and continuous radiation from an x-ray tube. For N₂, partial N1s absorption cross sections are derived and the oscillator strengths for the vibrational and Rydberg transition series are evaluated from the measurements carried out with due account of the background and instrumental distortions.     

Reduced population and gain coefficient calculations for soft X-ray laser emission from Eu

Energy levels, transition probabilities and effective collision strengths for the 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰, and the 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4l (l=s, p, d, and f) states of nickel-like Eu are used in the determination of the reduced population for 55 fine structure levels over a wide range of electron densities (from 10⁺²⁰ to 4×10⁺²² cm⁻³) and at various electron plasma temperatures.The gain coefficients for those transitions with positive population inversion factor are determined and plotted against the electron density.     

Perturbative QCD calculation of jet cross sections in e+e− annihilation

We calculate the α_s² to three-jet cross sections in e⁺e^? annihilation in a scheme that uses regulator masses for the infrared and collinear divergences. Using various methods to define the three-jet region, we find that the corrections to the O(α_s) cross sections are large.     

稀土离子Ho+,Ce+,La+与H2碰撞的单电子俘获截面测量

在复旦大学加速器实验室的３０ｋｅＶ同位素分离器上，使用新近建立的一套用于单价离子与气体分子碰撞的单电子俘获截面测量装置，测量了５—３０ｋｅＶ Ho⁺,Ce⁺,La⁺与H₂碰撞的单电子俘获截面．实验发现中空型离子源的阳极电压的变化对于稀土离子的亚稳态比例有一定影响，同时造成了单电子俘获截面的很大变化，而阳极电压对Ａｒ⁺的影响很小．还对实验结果进行了分析 关键词：     

Angular distribution and polarization of photons during resonant above-threshold scattering on an atom

The effect of the resonant structure in the continuous spectrum induced by an external laser field due to the coupling of continuum states with the 1s4s ¹ S level in helium on cross sections of elastic and inelastic scattering of probe radiation on an atom in the metastable 1s2s ¹ S state at an energy above the ionization threshold is theoretically studied. Explicit expressions for the angular distribution and the degree of polarization of scattered photons as functions of probe and laser radiation characteristics are derived in the rotating wave approximation. Frequency, angular, and polarization dependences of the cross sections of scattering into final 1s ^{2 1} S, ¹ s2s ¹ S, and 1s4s ¹ S atomic states are calculated.     

Positron-hydrogen-like-ion scattering

Scattering of positrons by hydrogen-like-ions (He⁺, Li²⁺, Be³⁺ and B⁴⁺) has been studied using two variants of the polarized orbital method. The positronium formation channel has not been included in the calculations,s-wave phase shifts obtained using the two variants differ appreciably from each other. Moreover, the polarized orbitals-wave phase shifts fore ⁺-B⁴⁺ scattering differ from the corresponding variational results qualitatively in the low energy region. The differential cross sections are reported.     

Screening effects in secondary electron production by equal velocity H+, H+2, He+, He++ions

Electron spectra produced by equal velocity (0.75 MeV/amu) H⁺, H⁺₂, He⁺ and He ⁺⁺ ions are shown. Screening effects are observed for He⁺ ions but not for H⁺₂. He⁺⁺ cross sections scale like Z² = 4 when compared to H⁺ cross sections.