摘要:

Slow highly charged ions approaching surfaces at very close distances (∼nm) are known to capture many electrons in highly excited states forming hollow atoms(1)(2). These hollow atoms quickly decay to their ground states through a long cascade of autoionization processes( Auger transitions) which may be balanced , as these ions are still close to the surface, by a series of electron captures. This actual sequence of many events of capture and autoionization, alternate or not, is not experimentally known to date, and depends on the charge of the ions and of the capture processes which may be very different above metals and insulators. We review in this paper two new experiments on the kinematics of fully decelerated highly charged ions(Ar18+) above dielectric and metal surfaces, and on the behavior of ions of lower charge states (O7+and Ne9+) above the same surfaces. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619651

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Cross sections for target atom and projectile ion K vacancy production have been measured using solid targets of Mo, Ag,and Sn bombarded by 10 MeV/amu beams of H, Ne, Ar, Cr, Kr, Mo, Ag, Sn, Xe, Nd, Ho, Ta, Au, and Bi. It was found that the target K vacancy production cross sections reach a local maximum as the projectile atomic number Z1approaches the atomic number Z2of the target. In this work, the measured cross sections are compared to the results of calculations based on existing theories of K‐vacancy production. It was found that the predictions of current theories of the molecular orbital mechanism describe the shape of the Z1‐dependence of the cross sections in the near‐symmetric collision regime reasonably well. The contributions from direct electron capture and ionization were represented by a second‐order polynomial in Z1because the validity of available theoretical descriptions of these processes does not extend into the near‐symmetric region. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619652

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

High‐resolution measurements of the K x‐ray spectra of metallic Ca, Ti, Cr, and Fe were performed with a von Hamos Bragg crystal spectrometer. The target x‐ray emission was induced by by 2–19 MeV/amu C, O and Ne ions. The energies of the well resolved K&agr;LNX‐ray satellite lines were determined. Based on the measured values the empirical formula for the K&agr;LNsatellite energy shift of the 3d transition elements is given. For the Ca and Ti target bombarded with C ions also the K&agr;hLNhypersatellite lines the K&bgr;LNsatellite lines and even the K&bgr;hLNhypersatellite lines have been measured and their energies determined. The possible variation of the energy differences between neighboring satellite and hypersatellite lines with the projectile energy and atomic number was probed. No significant dependence on the projectile characteristics was observed. In contrast to that the absolute energies of the satellite and hypersatellite lines lines were found to depend on the projectile velocity. This dependence was attributed to the M shell ionization of the target atoms accompanied to the K and L‐shell ionization produced in collisions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619653

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

L1(L3M1), L&eegr;(L2M1), L&agr;(L3M4,5), L&bgr;1(L2M4), L&bgr;3,4,6(L1M2,3+L3N1), L&bgr;2,15(L3N4,5), L&ggr;1,5(L2N1+L2N4), and L&ggr;2,3(L1N2,3) cross sections were used to find L sub‐shell cross sections which are compared with the ECPSSR theory. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619654

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

With the advent of the third generation synchrotron radiation, we can perform experiments on the threshold behavior of the satellites including the excitation dynamics in atoms. Especially, x‐ray emission spectroscopy is a suitable tool to study the satellites on the electron correlation. The contributions of direct ionization, i.e, the shake‐off process in Fe and indirect ionization of Coster‐Kronig transition in Au have not been investigated to the x‐ray emission spectra yet. We present the contribution of the spectator holes to the processes around the threshold. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619655

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Doubly excited KLL states ofC3+were populated by triple electron capture in collisions of fast bareC6+ions with Ar atoms. Measurements of the Auger electron emission at zero degree with respect to the beam direction were used to determine the absolute single differential cross sections for the triple electron capture to all autoionizing KLL states. In addition, independent particle model was utilized to predict the differential cross section for the population of all doubly excited states of carbon. Theoretical cross sections were critically compared with experimental results. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619656

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Monte Carlo (MC) simulation of charged particle track structure has become an important tool in radiation biology. MC calculations provide detailed spatial information on the production of radiation damage to DNA and other cellular structures. To test the physical parameters used in these models and to explore details of electron transport in condensed matter we have initiated a comparison of MC results to measured doubly differential yields of electrons emitted from thin foils by the passage of fast charged particles. Our initial studies focus on the calculation of differential electron yields resulting from passage of 1–2 MeV protons through thin carbon foils using the MC code PARTRAC developed at the Institute of Radiation Protection — GSF, Neuherberg, Germany. Preliminary calculations are in relatively good agreement with spectra measured for secondary electrons with energies larger than about 50 eV, however large variations are observed for smaller energies. The effects of changes in such parameters as electron mean free path, elastic and inelastic electron scattering cross sections, and foil thickness are illustrated. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619657

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We review recent developments in the process where excitation occurs together with ionization in collisions of helium with charged particles and photons. Various aspects of this process are discussed. The interrelation between cross section ratios for charged particle and photon impact is considered in the limit of first order perturbation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619658

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

It is well known that for very asymmetric collisions between a highly charged ion and H2near the RTE resonance, NTE is practically negligible. However, even though the interplay between RTE and NTE and their possible interference has been addressed formally and more recently by concrete calculations, experimentally very little work has been done on fast collision systems of increasing symmetry. We report on recent Auger electron RTE/NTE double differential cross section measurements of H‐like B4+ions in 4 MeV collisions with H2, He and Ar gas targets. Calculations using an atomic orbital close coupling (AOCC) method indicate NTE to be negligible for B4+collisions with H2, but possibly substantial (depending on screening considerations) for He and Ar targets. R‐matrix calculations are also presented for elastic (resonant and non‐resonant) electron scattering from B4+. Within the electron scattering model (ESM), the active target electron can be considered to scatter as a free particle with a momentum distribution governed by its Compton profile. Thus, a single R‐matrix calculation combined with the individual momentum distribution of each target should be sufficient to describe the RTE process. While this is found to be the case for H2and He, results for Ar are not in such good agreement, even allowing for the possibility of destructive RTE‐NTE interference. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619659

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The energy distributions of H+fragments produced in N7++ H2collisions at projectile energies ranging from 1.4 keV down to 32 eV have been investigated experimentally as a function of the detection angle. At 1.4 keV, two groups of peaks are clearly visible, especially at forward angles. The structure centered at energies lower than ∼ 20 eV, corresponds to a double capture at relatively large impact parameters, whereas the highly energetic protons result from capture events at very small impact parameters. The results from a quasiclassical calculation method show a good agreement with our experimental data for the fragment energy distributions. At the lowest projectile energy, the fragment energy is found to be independent on the detection angle. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1619660

出版商:AIP    

年代:1903

数据来源: AIP