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  • Articles  (11)
  • 34.80.Dp  (11)
  • Springer  (11)
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  • Articles  (11)
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  • Springer  (11)
  • American Institute of Physics
  • Elsevier
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  • 1995-1999
  • 1990-1994  (11)
  • 1965-1969
  • 1955-1959
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  • Physics  (11)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 55 (1992), S. 401-404 
    ISSN: 1432-0649
    Keywords: 34.80.Dp ; 42.55.Lt ; 52.80.Hc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spectral line shapes of the Ar+ 476.5 nm and 480.6 nm lines, excited in a He-Ar hollow cathode (HC) discharge, were measured using the Fabry-Perot technique. The collisional and Doppler linewidths were determined for the two lines. The collisional broadening constants are estimated to be (5±3) MHz/mbar and (6±3) MHz/mbar, respectively. The temperature obtained from the two Ar ion transitions was found to be 260 K higher than that expected for the rest of the gas mixture from earlier measurements. The possibility is discussed, that this excess temperature is caused by Ar ions partially created in the HC discharge by charge transfer collisions with He 2 + molecules.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 24 (1992), S. 155-160 
    ISSN: 1434-6079
    Keywords: 34.80.Dp ; 34.50.Fa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method for measuring cross sections for electron-impact excitation out of the metastable levels of the He atom is described. A hollow cathode discharge is used to produce an atomic beam consisting of ground-level He atoms and the He(21S) and He(23S) metastable atoms. An electron beam of energy below 20 eV crosses the atomic beam exciting the metastable atoms to higher levels, and the intensity of the radiation emitted by atoms in these higher levels is utilized to determine the cross sections. Because of the very low concentration of metastable atoms in the atomic beam, the emission signal is extremely weak. A number of special techniques have been developed to detect these very low-level signals. Absolute calibration of the cross section is accomplished by referencing the emission signal that resulted from electron excitation out of the metastable level to the emission signal that resulted from the 23S→33P or 21S→31P laser optical absorption.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 23 (1992), S. 137-144 
    ISSN: 1434-6079
    Keywords: 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We studied the electron impact excitation of the (2 P 1/2) ns [1/2] J=1 states in Ne (n=3) and Ar (n=4) using the electron-photon polarization correlation technique. The two linear Stokes' parametersP 1 andP 2 have been measured in Ne at an impact energy of 50 eV and in Ar at 30 eV and 40 eV for electron scattering angles up to 40° (up to 50° in Ar at 40 eV). In addition, previous measurements in Ar at 50 eV have been extended to scattering angles of 40° in an effort to facilitate a more meaningful and broader comparison of the Ar results obtained at different impact energies. Two of the four independent parameters required for a complete description of the excitation process, the alignment angle γ and the linear polarizationP lin + of the angular part of the collisionally induced excited state charge cloud were extracted from theP 1 andP 2 measurements. A comparison with theoretical predictions from first-order perturbative theories such as a distorted-wave Born approximation (DWBA) and a first-order many-body theory (FOMBT) revealed a generally good agreement between experiment and theory in Ne and Ar at 50 eV except for some discrepancies at scattering angles above 30°, whereas the agreement between experiment and theory was much less satisfactory in Ar at 30 eV and at 40 eV over the entire range of scattering angles studies in this work. We found that the measured coherence parameters appear to be shifted systematically towards larger scattering angles compared to the theoretical predictions as the impact energy is decreased.
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  • 4
    ISSN: 1434-6079
    Keywords: 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron-impact double ionization of noble gases is investigated theoretically for the case of high incident energies (5 keV). An ab initio calculation is made including partial correlation in the initial state as well as in the final state. The results of the calculations are compared with those of other theories and with the first available (e, 3e) experimental data on krypton 4p 6.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 23 (1992), S. 287-293 
    ISSN: 1434-6079
    Keywords: 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The formulation of approximations for the calculation of the (e, 2e) reaction on atoms is considered. The range of validity of the two common working approximations, the distorted wave Born and impulse approximations, is illustrated. A feasible approximation that treats the reaction in more detail is derived.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 23 (1992), S. 331-339 
    ISSN: 1434-6079
    Keywords: 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method is proposed for approximately computing the post collisional interaction of the two escaping electrons in otherwise standard first order ionisation calculations. At intermediate energies and in asymmetric kinematics the effects are found to be very small. The interactions of these electrons with the residual ion are considered through the use of distorted waves. For the slow one the latter are used in the calculations but for the fast one their effect is investigated using Fourier transforms. These interactions play a significant role.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 23 (1992), S. 371-376 
    ISSN: 1434-6079
    Keywords: 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Triple differential cross sections have been measured in the vicinity of the (2s 2)1 S autoionising state of helium, following impact by 200 eV electrons. The scattered electron detector was set at an angle of −12° (anti-clockwise) and the forward and backward ejected electron angular ranges scanned. The direct ionisation cross section at an ejected electron energy of 33.5 eV has been obtained and the results for the resonant ionisation of the1 S state are presented in the Shore/Balashov parametrisation. These measurements are compared with previous experimental data and emphasise the need for new detailed theoretical calculations on the autoionisation process.
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  • 8
    ISSN: 1434-6079
    Keywords: 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report new measurements of the absolute electron-impact double ionization cross sections for Ar and Kr and of the ratios of double-to-single ionization for impact energies from threshold to 200 eV using the crossed electron-beam — fast-atom-beam technique. The work was motivated by the recently highlighted spread of about 30% in the Ar2+/Ar+ ionization cross section ratios obtained by several groups using different experimental techniques. Such a spread is inconsistent with statistical uncertainties of typically 3% or less that were quoted for the various reported ratios. A similar situation exists for Kr where the spread among the recently published Kr2+/Kr+ ionization cross section ratios is about 15%. We made an attempt to identify all potential systematic errors inherent to the fast-beam technique that could affect the measurement of cross section ratios with special emphasis on those systematic errors that could influence the detection of singly and doubly charged product ions differently. We found Ar2+/Ar+ and Kr2+/Kr+ cross section ratios of, respectively 0.066 ±0.007 and 0.087 ±0.008 at 100 eV which confirm earlier measurements using the same experimental technique. The error limits on cross sections ratios measured in our fast-beam apparatus were determined to be at least ±9% for cross section ratios of multiple-to-single ionization for the same target atom and at least ±10% for ratios of single ionization cross sections for different target species. Our error limits are dominated by systematic uncertainties of the apparatus which do not cancel when cross section ratios are measured, since the ratios are obtained under similar, but not identical experimental conditions.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 23 (1992), S. 295-300 
    ISSN: 1434-6079
    Keywords: 32.80.Fb ; 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Multiply differential cross sections for two- and three-electron escape are parametrised in terms of generalised tensorial asymmetry parameters. The analysis is based exclusivly on rotational invariance as an exact symmetry for the experimental set up. No approximate assumptions are made on the correlated dynamics of many- electron systems. Results are valid for any atomic and molecular target. The new parameters may be used to describe experimental and theoretical data in a compact way, but also to link e.g. coincidence and non-coincidence measurements with each other.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 23 (1992), S. 301-308 
    ISSN: 1434-6079
    Keywords: 31.20 ; 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The distorted-wave Born approximation (DW-BA) is discussed and samples of calculations are presented for ionization of the 2p inner shell of Ar, the 5p, 5s and 4d shells of Xe, and for ionization of He in asymmetric perpendicular plane geometry. Agreement with measurements of inner shell ionization of Ar is excellent. It is pointed out that triple differential cross sections for ionization of heavy atoms can exhibit much structure, which presents a challenge to both theory and experiment. Particular cases of 5s and 4d ionization of Xe are given as examples of situations worthy of experimental investigation. Comparison is made with very recent measurements of ionization of He in asymmetric perpendicular plane geometry. In agreement with experiment, DWBA shows at all incident energies a single main peak at φ=180°, where φ is the angle between the outgoing electrons. It is demonstrated that at high energies this peak arises from a double collison mechanism. This contrasts with energy-sharing ionization into the perpendicular plane where the double collision mechanism, dominant at high energies, gives a peak at φ=90°, and where with reducing energy this peak is replaced by one at φ=180° coming from the single collision mechanism. Suggestions are made for further experiments.
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  • 11
    ISSN: 1434-6079
    Keywords: 34.80.Dp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Differential and integral cross section data for electron-impact excitation of the 21 P level in He have been critically reviewed. Experimental and theoretical results have been compared and a set of differential cross sections at 20° scattering angle in the 25 to 500 eV impact energy range has been deduced based on all available information. It is proposed that this set of data represents the most accurate inelastic differential cross sections available at the present time and could be used as a secondary standard for normalization of cross sections.
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