Multiphoton induced x-ray emission from Kr clusters onM-shell (∼100 Å) andL-shell (∼6 Å) transitions
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Experiments demonstrating the role of cluster formation on multiphoton-induced x-ray emission and the scaling of this phenomenon into the kilovolt range have been performed on Kr. For the Kr M shell, augmentation of ${\mathrm{Kr}}_{\mathit{n}}$ formation leads to a large increase in ${\mathrm{Kr}}^{9+}$ (4p\ensuremath{\rightarrow}3d) emission (\ensuremath{\sim}100 \AA{}) and the appearance of a strong band at \ensuremath{\sim}90 \AA{}. The observation of L-shell transitions (\ensuremath{\sim}5--7.5 \AA{}) demonstrates the scaling of this phenomenon into the kilovolt region and leads to the conclusion that the interaction produces direct inner-shell excitation with the emission of prompt x rays.Keywords:
Electron shell
The energies and intensities of the $2^{3}P_{1}\ensuremath{\rightarrow}1^{1}S_{0}$, and $2^{1}P_{1}\ensuremath{\rightarrow}1^{1}S_{0}$ transitions in He-like sulfur ions, and of the $2^{2}P\ensuremath{\rightarrow}1^{2}S$ transition in H-like sulfur ions have been studied as a function of the thickness and electron density of the solid through which the ions travel. The thickness dependence of the x-ray intensities was analyzed in terms of a three-component model description of $K$-shell vacancy production and decay. Cross sections for electron excitation or ionization and capture deduced from this analysis were used to establish the energies of the x-ray peaks for complete emission in vacuum (i.e., outside the target). Energy shifts were obtained by comparing the peak energies for emission in thick targets to those for emission in vacuum. The results show that the energy shifts increase approximately linearly with the square root of the valence electron density of the target and are in good agreement with theoretical expectations.
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Transfer and excitation, resulting from simultaneous electron capture and K-shell excitation in a single collision, has been measured 280--310-MeV ${\mathrm{Ti}}^{20+}$ ions channeled in the 〈100〉 axis of a thin Au single crystal. The 19+ charge-state fraction of the Ti ions exiting the Au crystal was measured as a function of ion energy and showed no narrow peak attributable to resonant transfer and excitation (RTE). The number of Ti K\ensuremath{\alpha} x rays, emitted by the Ti ions due to RTE, in coincidence with ${\mathrm{Ti}}^{19+}$ was also measured at two energies, on and off the previously reported narrow resonance, and again no evidence for a narrow resonance was observed.
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Electron capture from the K-shell of a negative ion by protons is considered by accounting for the interplay between the final channel-distorted projectile and off-shell electronic scattering motions using the distorted strong-potential Born approximation. The distorted motion accounts for the ionized state of the target core and the short-range shielding of the K-shell by the passive outer-shell electrons. Total cross sections versus incident energy are compared for the negative-ion, neutral, and singly-ionized forms of the second- and third-row elements C, O, F and Si, S, Cl. Target core neutrality and diffuseness of the negative-ion screening consistently lower the cross section by amounts ranging from 22 to 37% while the positive-ion results are larger by only 1 to 15%. Previous comparison with experiment and coupled-Sturmian-pseudostate results for neutrals has shown very good agreement.
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The impact parameter dependence of L-shell excitation in Ag+Ag and Ag+Cs collisions has been investigated both experimentally and theoretically. At collision energies of 17, 26 and 40 MeV, collisionally induced L X-rays have been observed in coincidence with scattered ions. The ions have been detected in a position-sensitive multi-wire proportional chamber. The (relative) number of excited L-shell electrons has been deduced for impact parameters b in the range 0.005 au
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We present in this paper some experiments on the interaction of slow ${\mathrm{N}}^{6+}$, ${\mathrm{O}}^{7+}$, and ${\mathrm{Ne}}^{9+}$ ions below C or Si surfaces carried out by looking at the projectile and target x rays. The study of the x rays emitted by the ions, in contrast with studies of Auger electrons, allows the observation of a much larger part of the decay, not yet explored, below the surface. Moreover, the x rays emitted by the target atoms may identify the shell from which the electrons are captured. It is shown that the electron promotion mechanism, previously observed, which transfers, e.g., K electrons of C targets into the L shell of these ions, represents only a very small part of the interactions occurring at the first atomic layer and that the neutralization takes place, below the surface, mainly via Auger neutralization.
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The dynamics of the first capture and decay processes occurring during the interaction of slow highly charged ions below a surface has been studied in looking at the x rays emitted directly, or in coincidence, by impinging bare or hydrogenlike ions of various atomic numbers on solid targets. Some results on the decay processes of these hollow atoms, mainly formed below the surface, for argon, iron, and krypton ions are presented. By measuring the changes of the number of electrons in the L and M shells of the ions, compared to the lifetime of the K shell, it has been possible to evaluate the mean time for the filling of the L and M shells. These measurements are compared with a model of interaction of the ions with the surface. \textcopyright{} 1996 The American Physical Society.
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K\ensuremath{\beta} x-ray lines from partially M-shell-ionized ions of titanium through nickel which are produced in vacuum-spark plasmas have been observed systematically for the first time, using a high-resolution curved-crystal spectrometer. Each K\ensuremath{\beta} line is clearly separated into its corresponding charge state. As a result, it is possible to measure the K\ensuremath{\beta}-type transition energies of the M-shell-ionized ions. The transition energies accurately determined are compared with those calculated for iron ions, and the agreement is excellent except for ions having some additional 3d outer-shell electrons or 3s inner-shell vacancies. The square root of the K\ensuremath{\beta} transition frequency is expressed as a linear function of the nuclear charge for isoelectronic sequences. The effective nuclear charges have been also determined for each K\ensuremath{\beta} transition. The 3p electrons do not affect the effective nuclear charges.
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We have measured the total cross section for photodetachment of the Na- ion over the photon energy range 30-51 eV. Electron detachment leads predominantly to the production of Na+ ions in this energy range. The structures in the measured cross section are associated with correlated processes involving the detachment or excitation of a 2p core electron, processes which are often accompanied by the excitation of one or more valence electrons. The most prominent feature in the cross section is a strong resonance associated with the excitation of a 2p electron from the core and a 3s valence electron. As in previous experiments on double excitation of valence electrons, electron correlation is seen to play an important role in the dynamics of negative ions.
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