J. M. Hall

Radiative auger effect in ion-atom collisions

Abstract The radiative Auger effect, RAE, is observed for Al and Si bombarded by 1–2 MeV H + . This is the first observation of the RAE X-ray edge using ion excitation. The KL 23 L 23 RAE edge energy and the relative intensity are in agreement with the previously reported electron and photon induced spectra.

A Study of Transfer Excitation in F8+ + He, Ne and Ar Collisions

High resolution x-ray spectroscopy has been used to measure F K x rays resulting from the decay of doubly excited two electron states formed during F8+ + He, Ne, or Ar collisions. The energy range spanned by the spectrometer includes the 2s2p(3P) ¿ 1s2s(3S), 2s2p(1P) ¿ 1s2s(lS), 2p2(1D) ¿ 1s2p(1P), 2p2(3P) ¿ 1s2p(3P) and the 2p2(1S) ¿ 1s2p(1P) transitions. These states may be formed by nonresonant transfer excitation, in which electron excitation is coupled with electron capture to an excited state, or by resonant transfer excitation, a process related to dielectronic recombination, in which the capture of a loosely bound target electron results in projectile electron excitation. Calculations have been performed to estimate the contribution of each process to the total measured cross section.

One- and two-electron processes in collisions of heavy ions with H2 and He

Abstract In this paper we present a description of the apparatus and results for experiments involving one- and two-electron processes in collisions of heavy ions with H2 and He. The experiments were performed using one-electron and bare projectiles. In the first section we describe the measurement of pure ionization of one-electron projectiles by H2 targets and compare with previous results for He targets. We also present the results for one-electron capture by the projectiles from H2 targets. The energy dependence of the cross sections is compared to theoretical predictions for atomic and molecular hydrogen targets. Both experiments were performed by measuring only the final charge state of the projectile. In the second section we describe the measurement of partial cross sections for the same collisions by measuring the target recoil charge state in coincidence with the projectile charge state. By this method we can measure pure single- and double-ionization of the target, pure single-electron transfer and transfer ionization, and pure double-electron transfer. This experiment is presently being performed for bare fluorine on He; however, absolute cross sections are not available at the time of this conference.

Radiative electron rearrangement: a proposed description for low-energy satellites observed in ion-atom collisions

The authors propose a satellite sequence as an explanation of the low-intensity peaks observed just below the energy of the K alpha 1,2 normal X-ray line. The sequence, (1s)-1(2p)-n to (2s)-2(2p)-n+1(n=1-4) radiative electron rearrangement (RER), gives good agreement with previously measured peak energies for Z between 11 and 22.

Enhancement of radiative electron rearrangement in Si by He+ bombardment

Abstract The first multiple ionization peak in the radiative electron rearrangement (RER) satellite sequence shows an order of magnitude enhancement relative to Kα 1,2 radiation in He + induced spectra compared to H + or e − induced X-ray spectra of Si. This enhancement supports the RER model which requires that the rearrangement decay increases proportionally with the first Kα 1,2 satellite decay.

Single electron capture by high velocity bare and one-electron projectiles in collisions with molecular hydrogen

Abstract Total cross-sections for single electron capture by 0.5–2.4 /amu bare and hydrogen-like F and O projectiles on molecular hydrogen have been measured. The measured cross sections are compared with empirical scaling rules and are found to scale as E −4.82 and q 3.75 .

Single electron capture by 0.5-1.5 MeV/u F9+ and F8+ on hydrocarbon gases

Total cross sections are reported for single electron capture by bare and one-electron fluorine ions incident on the hydrocarbon gases CH4, C2H4, C2H6, C3H6 and C3H8. The measurements span an energy range of 0.5–1.5 MeV/u. The hydrocarbon series was selected to further investigate the extent of validity of the additivity rule for molecular targets whereby a molecular cross section is considered to be the sum of the atomic cross sections of the constituent atoms in the molecule. An analysis of the systematic trends shows that no deviations from strict additivity are observed over the entire energy range. Using the simple model from additivity, atomic carbon cross sections are extracted from the molecular cross sections. The consistency of this model for these measurements is explained in terms of the large relative capture from inner-shell carbon atoms and by the low probability for secondary effects within the target molecules.

Simultaneous electron capture and target ionization in bare-fluorine-helium collisions

Abstract Projectile final charge states were measured in coincidence with recoil ion final charge states for a bare fluorine beam incident on a helium gas target. Absolute partial cross sections were determined for pure single target ionization, pure double target ionization, pure one-electron capture, and transfer ionization in the energy range 7–38 MeV. The four types of events were collected simultaneously by measuring the time of flight of the recoil ions and by charge-state analyzing the projectile beam using a position-sensitive detector. The pure-capture and transfer-ionization cross sections were corrected for pure ionization of the helium by contaminant hydrogenlike fluorine in the projectile beam. This correction was found to be as large as 50% in the case of the high-energy cross sections. The correction is much larger for pure capture than for transfer ionization; therefore, the relative contributions of these channels to total one-electron transfer are shifted relative to the uncorrected values.

An Experimental Apparatus for Low Energy High Charge Heavy Ions to Study Collisions on Atomic Hydrogen

The design and performance of a recoil ion source system which includes a recoil ion source, atomic hydrogen thermal oven target and an electrostatic analysis system will be discussed. The recoil ion source produces low velocity highly charged ions via collisions between heavy fast pump beams from the EN tandem accelerator and target gases. Time-of-flight techniques provide initial recoil charge state separation. Collisions of the recoils with atomic hydrogen are being studied. The atomic hydrogen is provided by a thermal oven which features long life time operation and low input power requirements. Dissociation fractions of 80% are achieved for 300 watts of input power. A hemispherical electrostatic analyzer allows the final charge states of the recoil ions to be determined thereby allowing the measurement of charge exchange processes for an energy range of 100 eV/q to 5000 eV/q for the incident recoil ions.

Electron Capture Cross Sections for Low Velocity Neq+ (q = 2,3,4,5 & 6) Incident upon Atomic Hydrogen

Measurements of electron capture cross sections for low velocity Neq+ ions (q = 2,3,4,5 & 6) in collisions with atomic hydrogen will be discussed. The Ne ions are obtained from a recoil ion source using a F4+ pump beam from the EN tandem accelerator. Time-of-flight techniques and post interaction electrostatic analysis provide for the experimental determination of the electron capture cross sections. Comparisons to the theories of Olson and Salop and Ryufuku et al. will be presented.