The angle, energy, and fluence dependence of electron emission following the interaction of normally incident 100-MeV Ne + ions with thin polypropylene foils and 170-MeV Ne + projectiles with Mylar foils has been investigated experimentally.Spectra were taken for electron ejection angles of 0', 45', and 120' at

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We present experimental evidence for a deceleration of convoy electrons produced by 5 MeV͞u ions (N 71 , Ne 101 , S 131 , Ni 231 , and Ag 371 ) during the interaction with insulator foils at normal incidence. The deceleration first increases with increasing projectile charge, reaches a maximum at a projectile charge of about 16, and seems to approach zero for even higher charges. Different possible mechanisms and quantitative estimates for the slowing down of convoy electrons are presented.[ S0031-9007(97) PACS numbers: 34.50. Fa, 72.20.Jv, 73.61.Ph, 79.20.Rf Electron spectra in ion-solid interactions show, apart from Auger lines and binary-encounter electrons, one prominent structure exactly in the projectile flight direction: the convoy-electron peak. Convoy electrons are fast electrons that leave the solid surface with about the same velocity as the projectile ion. They give rise to a cusp shaped kinematic peak and are related to the attractive Coulomb potential of positive ions. This peak was first measured in ion/atom collisions experiments [1] and shortly after for ion-solid interactions [2]. In both cases convoy electrons are produced by electron capture (ECC) [3] and by electron loss to continuum states of the projectile (ELC) [4,5]. In dense matter, these electrons are subject to a random walk under the influence of the target constituents and the projectile potential [6].Convoy electrons can be accelerated by the imagepotential of the projectile charge, as has been found for ions under glancing-angle scattering conditions at semiconductor and metal targets [7][8][9] and at normal-incidence conditions for highly charged ions at a proton-equivalent energy of 5 MeV͞u [10]. In ion-insulator interactions ionizing collisions result in a positive nuclear-track potential, which can decelerate target Auger-electrons emitted from the insulator surface [11] and accelerate desorbed positive hydrogen ions [12]. In this Letter we present first evidence for a deceleration of convoy electrons induced by 5 MeV͞u highly charged ions traversing insulating polypropylene ͓͑C 3 H 6 ͔ n ͒ foils at normal incidence.A detailed description of the experimental setup has been published previously [10,11]. 5 MeV͞u heavy ions were delivered by the heavy-ion cyclotron of the Ionenstrahl-Labor (ISL) at the Hahn-Meitner Institut. The beam was sent through a post-cyclotron stripper foil and a magnet to select projectiles with a charge-state close to equilibrium. The beam of 0.1 to 10 particle nA was collimated to about 1 mm 2 at the center of the magnetically shielded target chamber with a vacuum of typically 10 26 mbar. During the experiments the targets were wobbled in both directions perpendicular to the beam for an accurate fluence determination and for a reduction of the heat load. For the measurement of convoy-electron spectra an electrostatic zero-degree tandem spectrometer (energy resolution DE͞E 0.6% and solid angle DV 2 3 10 25 sr) was used [13]. The ions pass the first stage of the spectrometer and electrons emitted in t...

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Differential ionization cross-sections for 40 MeV H + + He collisions were measured as a function of electron energy, electron ejection angle and final recoil ion charge state. Coincidences between recoil ions and emitted electrons were taken for electron ejection angles of 55" and 125" and energies between 3 and 500eV. Good agreement is found between measured energy distributions of ejected electrons and results of standard first-order perturbation theory in the case of single ionization. The experimental double-ionization cross-sections, however, are found to exceed independent-electron model predictions by more than an order of magnitude. Furthermore, evidence is provided that this deviation is mainly due to initial-state correlation.Introduction. -Double ionization of helium by ion impact has been studied extensively in the energy range 1-15 MeV/a.m.u. [l-31. In this energy range, the first Born approximation is valid for single ionization by proton impact, whereas it is not for double ionization as proved by the fact that the ratio between single-and double-ionization cross-sections depends on the sign of the projectile charge Zp. In other terms, the double-ionization cross-section does not vary as Zf for small 2, as the single-ionization cross-section does. The actual behaviour of the ratio between single-and double-ionization cross-sections has been discussed by many authors (for a review, see [4,5]). However, only one calculation reproduces correctly the difference between double ionization by protons and antiprotons [6]. Tentatively, various mechanisms have been suggested as listed, e.g., in [4]: ground-state correlation, TS-1, TS-2, shake-off, exchange contribution, scattering correlation. These concepts are often used without an unambiguous definition and may not be independent. Furthermore, interference between them or between first and second order of perturbation theory have been invoked. However, total cross-sections correspond to averages (over DAAD fellow.