Excitation of autoionizing states of helium-like ions by scattering of high-energy particles

The cross sections for two-electron excitations of helium-like atomic systems into the autoionizing 2s ² (¹ S)- and 2p ² (¹ S)-states by collisions with high-energy electrons and photons are deduced. The evaluations are performed to the leading order of non-relativistic perturbation theory. The analytical formulas for cross sections are obtained in the form of universal scalings. A comparison of our theoretical predictions with available theoretical and experimental results for the helium atom is made.     

Ionization of helium-like ions with excitation of nl states by high-energy photon scattering

The kinetic and spectral characteristics of the complex dielectric constant of a Ce: YAG crystal under laser irradiation in 250–275 nm spectral range are investigated. The lifetimes of free charge carriers and charge carriers, localized at the lattice defects (color centers), are estimated. It was established that photoconductivity signal of the sample is essentially caused by one-photon ionization processes from the ² F _5/2 ground state of Ce³⁺ ions.     

Scaling of cross-sections for asymmetric (e, 3e) process on helium-like ions by fast electrons

An approximate simple scaling law is obtained for asymmetric (e, 3e) process on helium-like ions for double ionization by fast electrons. It is based on the equation (Z ^′3π) exp[-Z(r₁ + r₂)],Z′ = Z – (5/16) for ground state wave function of helium-like ions and Z^′2 scaling of energies. The scaling law is found to work very well if the lower energy electron is ejected along the momentum transfer direction and the other one is ejected in the opposite direction. It also works quite well if this electron is ejected within about 90° of the momentum transfer direction with the other electron going in the opposite direction. The scaling law becomes increasingly accurate as the target nuclear charge and the energy increase.     

Two-electron excitation in helium-like ions by electron impact

Calculation of cross-sections for the two-electron excitation in helium-like ions by electron impact employing Coulomb-Born-Oppenheimer (CBO) approximation is presented. Analytical expressions for the differential and total scattering cross-sections without using partial wave expansion of the wavefunction reported earlier have been used. The total and differential scattering cross-sections for each of the excitations 1s ^{2 1} S* → 2s ^{2 1} S ^e , 2s2p ^1.3 P ⁰, 2p ^{2 1} S ^e ,³ P ^e,¹ D ^e in Be²⁺ and B³⁺ are computed. Results for Li⁺ reported earlier are also included for comparison.     

Electron capture by fast protons from helium-like ions

Four-body formalism of boundary corrected continuum intermediate state (BCCIS-4B) approximation have been applied to calculate the single-electron capture cross sections by fast protons through some helium-like ions in a large energy range from 30–1000 keV. In this model, distortion has been taken into account in the entrance channel. In the final channel, the passive electron plays the role of screening of the target ion. However, continuum states of the projectile and the electron in the field of the residual target ion are included. The comparison of the results is made with those of other theoretical investigations and experimental findings. The present calculated results are found to be in good agreement with the available experimental findings.     

Hole states in helium-like ions

An analysis is made of the poles of the single-particle Green's function of helium-like ions in which electron correlation is taken into account on the basis of the model of singly filled orbitals. The energy of Hartree-Fock pole calculated through the use of the hydrogen-like wave functions for the orbitals turns out to be approximately equal to the exact value. The second pole, which corresponds to a different hole state, has a residue which vanishes as z increases and must be considered fortuitous.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 90–93, April, 1971.     

Two-electron excitations in helium-like ions by inelastic photon scattering

Inelastic photon scattering by helium atoms and helium-like ions with simultaneous excitation of the two-electron transition 1s ²→2s ² is examined in the nonrelativistic energy range I≪ω≪m (I is the ionization potential, ω is the photon energy, m is the electron mass, and ℏ=c=1). The electrons are assumed to be moving in the Coulomb field of the nucleus, and the electron-electron interaction is taken into account in the lowest perturbation order. The differential and total cross sections of the process and the autoionization width of the 2s ² energy level are calculated. The numerical value of the autoionization width is found to agree with the results of the more rigorous calculations of other researchers. Zh. éksp. Teor. Fiz. 113, 539–549 (February 1998)     

Detection of high-energy electrons by a directional spectrometer

A method for the detection of 26- and 28-GeV electrons by a directional spectrometer based on oriented tungsten, tungstate, and garnet crystals has been reported. In spite of an anomalous character of the development of an electromagnetic shower at the initial stage in a crystal oriented along the 〈111〉 axis, the relative energy release of the shower in the spectrometer behind the crystal at the final stage is described by the standard dependence of the development of the electromagnetic shower.     

Quasielastic rho-meson knockout from nucleons by high-energy electrons

The electroproduction of charged rho mesons on a nucleon under conditions of quasielastic kinematics [Q ² > 2 (GeV/c)², W > 3 GeV, and ω _ρ ? q ⁰ in the laboratory frame] is considered. The main diagrams involved in this process are taken into account, and it is shown that the case of rho-meson knockout by a longitudinal photon is dominated by the t-channel pole diagram featuring a rho meson, so that direct rho-meson electroknockout makes a leading contribution to the process being considered. Questions concerning the gauge invariance of the electroproduction process are considered in detail, along with contact terms that inevitably arise in employing form factors in ρNN vertices and which are necessary for restoring gauge invariance. It is shown that the structure of these contact terms is not determined exclusively by the requirement that the electroproduction amplitude be gauge-invariant and may be such that the corresponding correction to the dominant diagram due to these terms proves to be suppressed in the quasielastic region (with increasing Q ²), with the result that the t-pole process featuring a rho meson remains dominant; at the same time, the contribution of this correction is significant at low Q ² or in the case of photoproduction, modifying substantially the electroproduction cross section.     

The spectra of helium-like ions in laser-produced plasmas

We calculate intensities of lines arising from the n = 2 and n = 3 levels of highly-charged, helium-like ions in very dense plasmas. We determine the importance of recombination and cascading, and of radiation trapping, on certain line-intensity ratios, and we illustrate the relevance of these calculations to laser-plasma diagnostics. Finally, we outline the pitfalls inherent, at very high densities, in some other techniques commonly used to interpret plasma spectra.     

Nuclear reactions triggered by laser-accelerated high-energy ions

A technique is suggested for triggering nuclear reactions by accelerating ions with a powerful ultrashort laser pulse in a plasma. The underlying idea of the suggested compact “reactor” is utilization of high-energy ions accelerated by the charge-separation electrostatic field in the direction perpendicular to the laser beam axis in a gas-filled capillary. Accelerated ions with energies of several MeV penetrating the target from the inside surface of a channel give rise to nuclear reactions which can be used to create a compact source of fast neutrons and neutrons of intermediate energies for generating various (short-and long-lived, light and heavy) isotopes, for generating gamma radiation over a broad energy range, for making sources of light ion and induced radioactivity. The yield of the corresponding nuclear reactions as a function of the laser beam parameters has been investigated. The suggested technique for triggering nuclear reactions provides a practical tool for studies of nuclear transformation on the pico-and nanosecond scales, which cannot be achieved using other methods. Zh. éksp. Teor. Fiz. 115, 2080–2090 (June 1999)     

Spectrum of two quasiequal-energy electrons ejected by a high-energy photon

We present numerical results for the photoelectron spectrum in double ionization by keV photons in the quasiequal-energy sharing region. In this region of the spectrum, the relevant ionizing mechanism is due to a mutual sharing of the photon momentum by both electrons, with small momentum transferred to the atomic nucleus. Calculations were performed for photon energies of 25 and 50 keV, where retardation effects are fundamental, while final-state correlations are of minor importance. The spectra present a two-peak structure, with maxima located at the photoelectron energies , with the photon energy in atomic units. We discuss the general features of the spectrum in terms of the picture of the photoionization of two free electrons, and we propose a way of detecting the contribution by experiments. Received 24 January 2000     

Observations of high-energy electrons in the stratosphere

Summary To investigate the variation of the flux of cosmic radiation in the vicinity of the Earth, stratospheric balloon soundings are performed weekly at Campinas (Brazil). During some soundings, enhancements of the counting rates are detected. In this paper data from these excesses as well as their analysis are shown. It seems to indicate that possibly high-energy electrons are injected from the lower boundary of the radiation belt into the stratosphere.

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Riassunto Per ricercare la variazione del flusso delle radiazioni cosmiche in prossimità della Terra, sono fatti funzionare settimanalmente palloni sonda a Campinas (Brasile). In alcune sonde si registrano aumenti delle frequenze di conteggio. In questo lavoro si mostrano dati da questi eccessi nonché le loro analisi. Ciò sembra indicare che gli elettroni ad alta energia sono probabilmente immessi dallo strato inferiore della fascia di radiazioni nella stratosfera.

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Резюме для исследования изменения потока космического излучения в окрестности Земли еженедельно запускаются стратосферные шары-зонды в лаборатории Кампинас (Бразилия). Во время некоторых зондирований зарегистрированы увеличения интенсивности излучения. В этой статье приводятся данные измерений и их анализ. Проведенный анализ показывает, что эти случаи возможно связаны с электронами высоких энергий, инжектированными из нижней границы радиационного пояса в стратосферу.

     

Dispersion coefficients for interactions between two metastable helium-like ions

The dispersion coefficients C₆, C₈ and C₁₀ for the interactions between helium and helium-like ions in the metastable states of 2 ¹S and 2 ³S with Z up to 10 are calculated using variational wave functions in Hylleraas coordinates.     

Elastic scattering of high-energy electrons on atoms

A method is presented for the numerical calculation of the differential, total, and transport cross sections of elastic scattering, and results are given for the scattering of fast electrons with energies in the range 10 keV to 1 MeV on neutral atoms of uranium, silver, argon, aluminum, and oxygen. Approximations are obtained for the energy dependences of the scattering cross sections.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 8–12, January, 1980.     

Single photoeffect on helium-like ions in the non-relativistic region

We present a generalization of the pioneering results obtained for single K-shell photoionization of H-like ions by M. Stobbe [M. Stobbe, Ann. Phys. 7 (1930) 661] to the case of the helium isoelectronic sequence. The total cross section of the process is calculated, taking into account the correlation corrections to first order of the perturbation theory with respect to the electron–electron interaction. Predictions are made for the entire non-relativistic energy domain. The phenomenon of dynamical suppression of correlation effects in the ionization cross section is discussed.     

Electron impact optical excitation of helium-like ions in Coulomb-Glauber approximation

The Coulomb-Glauber approximation is applied to evaluate the electron-impact excitation integrated cross sections for 1¹ S —n ¹ P (n=2, 3) transitions in helium-like ions, C⁴⁺, N⁵⁺, O⁶⁺ and Ne⁸⁺. The results are presented in terms of scaled collision strengthn ³ Z ² k _i ² σ and scaled integrated cross-sectionZ ⁴σ. Our values when compared with other available theoretical results are found to be larger than the Coulomb-Born and distorted wave polarised orbital (DWPO) values.