Ionization of M subshells of Pb atoms by electron impact in an energy range of 5–30 keV

The relative intensities of the M ₅ N and M ₄ N satellites of Pb under electron bombardment of thick targets in the range of accelerating voltages U = 5?30 kV are experimentally investigated. Based on the previously proposed model of M X-ray emission, the relative intensities of these satellites are calculated using the total ionization cross sections of M subshells under electron impact found in different approximations. It is established that, among the models yielding analytical expressions for calculating total ionization cross sections, the model of classical binary collisions provides the best agreement with experimental data in the electron energy range under study. The parameters of the semiempirical Bethe formula for calculating the ionization cross sections of Pb M subshells under electron impact are determined.     

Charge exchange cross sections of carbon ions

Based on experimental data on the ion charge distributions, the cross sections of single electron loss σ _{i, i + 1} and single electron capture σ _{i, i ? 1} by carbon ions with velocities (2.7–8) × 10⁸ cm/s in different gaseous media (He, N₂, and Ar) have been obtained. Regularities of the cross section variation of the electron capture and loss by carbon ions as a function of the ion velocity, ion charge, and atomic number of the target have been for the first time studied in a wide range of the initial ion charge, from i = 0 to i = 6. A qualitative agreement of the obtained results with the published data has been established for a number of other ions. Theoretical calculations of the cross sections of single electron loss by carbon ions in helium have been carried out.     

Account of the fine structure of hydrogen atom levels in the effective emission cross sections of Balmer lines excited by electron impact in gases and plasma

The possibility of a correct account of the fine structure was shown for two limiting cases observed in beam and plasma experiments. A significant difference was found in the emission cross sections and the rate coefficients of direct and dissociative excitation of the H _α and H _β lines by electron impact in two limiting cases (e.g., this difference reaches an order of magnitude for dissociative excitation of the H _β line). The most reliable data on the cross sections and the rate coefficients of direct and dissociative excitation of the H _α and H _β lines by electron impact were found for both limiting cases. It was shown that, among the first four lines of Balmer series (rather easily detected), only the first two lines, i.e., H _α and H _β, can be currently employed in plasma spectroscopy studies because of the absence of data on the partial excitation cross sections of hydrogen atom nl-sublevels with n≥5.     

Oscillator strengths for the shape resonances in the N K absorption spectrum of NaNO3 measured with the use of synchrotron radiation

Spectral dependences of the total absorption cross sections near the N K(ls) ionization threshold have been measured in transmission for the first time for solid-phase sodium nitrate NaNO₃ using synchrotron radiation of the Russian-German soft x-ray beamline at the electron storage ring BESSY-II. On the basis of these measurements, which were performed with correct consideration of the background and instrumental distortions, partial N K absorption cross sections and the oscillator strengths for the π and σ shape resonances were determined for NaNO₃.     

Measurement of the absolute cross section for the elementary process of atomic field bremsstrahlung

Coincidence measurements of the absolute cross section for the production of bremsstrahlung by electrons in the field of gold atoms are reported. The incident electron energyT ₀ was 300 keV. Measurements were made for four different combinations of electron scattering angle and photon emission angle over a wide range of the relative photon energyk/T ₀ up tok/T ₀=0.83. The measured cross sections are compared with results of Bethe-Heitler and Elwert-Haug calculations     

Ionization function of magnesium for electron impact

Ionization cross sections for electron impact are measured with crossed beams of Mg atoms and pulsed electrons. Total numbers of particles are determined by the light emission of excited atoms. The ionization cross section obtained for electron energies from 7 eV to 60 eV has its maximum valueq _i (max)=7.8 · 10^?16 cm² at 12 eV electron energy.     

Asymptotics of the cross section for the electron loss by atoms and ions in light media

The dependence of the cross section of electron loss on the nuclear charge Z of a bombarding ion and on the nuclear charge Z _t of a target atom for fast collisions is studied theoretically using the plane-wave Born approximation and the sum rule. The results of calculations show that the cross section of electron loss for fast collisions increases monotonically as Z and Z _t increase, which can be used to interpolate cross sections for the processes for which there are no experimental data.     

Measurement of the absolute total electron impact cross section on Cs atoms using a magnetooptical trap

Laser cooling and trapping of neutral atoms has been employed for the measurement of the total electron impact cross sections of the ground state 6² S _1/2 of ¹³³Cs atoms in the energy range from 80 to 500 eV. The total electron impact cross sections of the cold Cs atoms in the MOT were measured by observing the decay of the MOT after the interaction with the electron beam, and were found to depend only on the electron flux and not on the total number of atoms in the MOT. We confirm and extend the existing data on these measurements.     

Total cross section for inclusive electron scattering in the lowQ 2 region

Absolute cross sections for inclusive electron scattering on H, D, Be, Al, and Si have been measured in the kinematical region 0.08 (GeV/c)²<Q ²<1.0 (GeV/c)² and 0.3 GeV<v<6.5 GeV. The measurements have been performed at incident energies of 3, 5, 6, and 7 GeV and at the fixed scattering angle of 10°. A careful treatment of radiative corrections due to elastic electron nucleus scattering, quasielastic and inelastic scattering on the bound nucleons has been applied to the measured cross sections. The comparison of the nuclear cross sections with the elementary ones leads to a value ofA _eff<A with a rapid onset of this effect at small values of the scaling variablex′.     

Electron impact ionization cross sections of the CO2 clusters

The modified Jain–Khare semi-empirical formalism for the evaluation of differential and integral electron impact ionization cross sections for molecules has been extended to the evaluation of cross sections for the electron ionization of CO₂ clusters: (CO₂)₂₄₀ and (CO₂)₁₇₀₀. The energy dependent differential cross sections are evaluated at the incident electron energies of 50, 100 and 200 eV. The integral total ionization cross sections have been calculated in the energy range varying from ionization thresholds to 1000 eV which revealed a good agreement with the available experimental and the theoretical data. The ionization rate coefficients have also been evaluated using the presently calculated ionization cross sections and Maxwell–Boltzmann energy distributions.     

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.     

Electronic excitation of HgX (X = Cl,Br, I) due to electron and methyl mercury halide collisions

Electronic excitation of HgX (X = Cl, Br, I) radicals in the B-state has been observed as the result of collisions with low energy electrons and methyl mercury halide (CH₃HgX) molecules. The emission intensity has been observed to be much weaker than that observed for electron-HgX₂ collisions under similar experimental conditions. Using the strongest band head of the B-X band system, an attempt has been made to calculate the emission cross section due to electron CH₃HgX collisions at 10 eV electron kinetic energy. For HgCl, HgBr, and HgI radicals, these cross sections are 1 × 10^-18, 7 × 10^-17, and 2 × 10^-17 cm², respectively, with an estimated uncertainty of ±30%. Our measured threshold electron energy for excitation of CH₃HgX molecules and observation of the B-X emission band system and emission cross sections measured at 10 eV are greatly different from those measured by Allision and Zare [Chem. Phys. 35, 263 (1978)].     

Anionic fragmentation of glycine upon potassium-molecule collisions

In this paper total cross sections (Q _T ) for electron impact on HCl and HBr are reported over a wide energy range from circa 0.1 eV to 2 keV. At impact energies below the ionization energy, the R-Matrix method is employed using Quantemol-N software whilst above the ionization energy the spherical complex optical potential (SCOP) method is used. It is shown that the two methods provide complimentary cross sections where they overlap. These calculations are compared with experimental and theoretical results wherever available.     

Elastic ν<Subscript>μ</Subscript><Emphasis Type="Italic">e</Emphasis> scattering as a source for determining the muonic neutrino mass and investigation of its electromagnetic properties

Electroweak (EW) and electromagnetic (EM) contributions to the cross sections of elastic scattering of muonic neutrinos by electron are analyzed. The effect of the neutrino mass and root-mean-square charge radius on the angular and energy distributions of product electrons and the total scattering cross sections is considered. The possibility of measuring the muon neutrino magnetic moment μ_ν by selecting its contribution to the ν_μ e-scattering cross sections is analyzed.     

The fate of Li and Be in stars and in the laboratory

We connect the observed under-abundances of Li and Be in dwarfs, with recent results on nuclear cross sections at low energies: for collisions of protons with atomic or molecular targets, the measured cross sections seem too high with respect to extrapolations for bare nuclei. Phenomenologically, these anomalous nuclear interactions can be described in terms of an effective screening potentialU _lab in the range of few hundred eV: in the presence of the electron cloud, nuclei become more transparent to each other as if the effective collision energy is aumented byU _lab. This implies that fusion cross sections are enlarged and at the same time elastic cross sections are lowered. If something similar occurs in stellar plasma, the nuclear burning temperatures are lowered, whereas diffusion processes are enhanced. We find that the observed Li and Be abundances in the Hyades and in the Sun can be reproduced for effective screening potentials of the plasma in the range of 600–700 eV, close to that found by experiments in the laboratory.     

Single- and double-electron charge transfer in collisions of α-particles with hydrogen molecules. II

Dependences of single-electron charge transfer cross sections on the molecule orientation are studied in collisions between α-particles and H₂ molecules in the ground state at collision energies E _c from 1 to 23 keV/u. Probabilities of single-electron capture were calculated in the independent electron approximation in the context of the close coupling equation method under the assumption that the hydrogen molecule consists of two independent hydrogen pseudoatoms. The total and partial single-electron capture cross sections averaged over all orientations of the molecule well agree with available experimental data at E _c > 5 keV/u.     

Structure and thermal stability of AgCu chiral nanoparticles

Theoretical studies of electron impact double ionization cross sections of Ne⁵⁺ and Ne⁶⁺ ions have been performed in the binary encounter approximation (BEA). Direct double ionization (DDI) has been investigated in the modified double binary encounter model. The K-shell ionization cross sections have been also calculated in the BEA to take into account the contributions to double ionization from the ionization-autoionization (IA) process. The effect of the Coulombic field of the target ion on the incident electron has been considered in the present work. Accurate expression of σ _ΔE (cross section for energy transfer ΔE) and the Hartree-Fock (HF) velocity distributions for the target electrons have been used throughout the calculations. The present results are in overall moderate agreement with the experimental observations. Possible reasons behind the discrepancies between the theory and the experiment have been discussed.     

Berechnung des Wirkungsquerschnitts der direkten Paarerzeugung bei Streuung von 5,511 MeV- und 32 MeV-Elektronen an einem statischen Coulombfeld

Differential cross sections for direct pair production by electrons with total energiesE ₀=5.511 and 32 MeV in copper are calculated in lowest order of pertubation theory and Born approximation, including the matrix elements of the electron exchange effect. Integration over particle angles and — in the case ofE ₀=32 MeV — over the energy of one outgoing electron was performed numerically on an IBM 7044 computer by using Gaussian quadrature formulas in FORTRAN-programs. The results forE ₀=5.511 MeV show a severe reduction of the differential cross section due to the exchange effect, while the results for 32 MeV are in fairly good agreement with the pair production experiment performed byCriegee in 1959.     

Study of cross sections for the loss of outer 1s, 2s, and 2p electrons by fast ions and atoms of light elements

In the case of light-element ions propagating with velocities V = 1.83 and 3.65 au in H₂, He, N₂, Ne, and Ar, the loss cross sections σ_{i, i+m} for m electrons (m = 1, 2, 3) are considered. The partial loss cross sections σ_i(nl) for one of the outer 1s, 2s, or 2p electrons are determined using the obtained data. It is shown that the experimental cross sections for the loss of the 1s and 2s electrons by positive ions qualitatively agree with the theoretical values calculated in the Born approximation. In the case of the ion velocity V = 1.83 au, the cross sections σ_i for 2p electrons are greater than the cross sections σ_i (1s) and σ_i (2s) by a factor of 1.2–3 for the same binding energies of electrons in the ion (I _nl > 20 eV). It is found experimentally that, at V = 1.83 au, the cross sections σ_i (2p) for I _nl ～ 10–20 eV are less than the cross sections σ_i (1s) by a factor of 2–3, which is probably caused by a decrease in the screening parameter (θ_2p < 1) of the outer shell of atoms.     

Fragmentation cross sections of32S at 0.7, 1.2 and 200 GeV/nucleon

We used CR39 plastic nuclear track detectors (C₁₂H₁₈O₇) in combination with automatic track measurement techniques to determine total charge changing and partial cross sections for the production of fragments of chargeZ _F =6 toZ _F =15 in collisions of³²S beam nuclei at energies of 0.7, 1.2 and 200 GeV/nucleon in targets H, C, CR39, CH₂, Al, Cu, Ag and Pb. By application of factorization rules measured partial cross sections are separated into pure nuclear and electromagnetic components. Total and partial cross sections for electromagnetic dissociation are compared with theoretical models. The energy dependence of pure nuclear cross sections is investigated.