J. P. Giese

Dielectronic Excitation and Recombination in Crystal Channels

In previous papers, in this volume, electron-ion recombination processes have been studied using either free-electron targets or targets of “almost-free” electrons which are loosely bound to atoms or molecules. In the former case, the techniques generally involve either merged electron-ion beams in “single-pass” configuration or in electron “coolers” in storage rings or observation of photons and associated charge state fractions in electron beam ion sources, in either the EBIS or EBIT configuration. These techniques are direct and, in the case of merged or crossed beam experiments, offer very high energy resolution.

Charge and angular correlated inelasticities in MeV/nucleon ion-atom collisions

Using an Elbek high-resolution magnetic spectrograph, we measured energy loss an angular distributions of MeV/nucleon projectile ions in coincidence with target recoil-ion charge state. We investigated collisions of 10 and 20 MeV C/sup 6 +/ on He, Ne, Ar, and Kr where the target atom is multiply ionized and the projectile emerges in charge state q or q-1. The amount of energy transferred to the continuum electrons exceeds, by far, the sum of the values of the ionization potentials and shows a strong target Z dependence. Both an n-body classical-trajectory Monte Carlo method (nCTMC) and an energy deposition model are used for comparison with the experimental data. 12 refs., 3 figs.

Differential charge state fractions of He following ionization by fast H− projectiles

Abstract The differential charge state fractions of He ions produced in ionization by fast H − projectiles have been measured at projectile scattering angles between 0.25 and 1.59 mrad and an impact energy of 1.0 MeV. These charge state fractions have been measured for each of the possible final charge states of the H − projectile (H − , H and p + ). Combined with earlier measurements of simple ionization (no change in projectile charge state) by protons and of capture and ionization by protons, some systematics can be noted. The fraction of doubly charged He ions exhibits a distinct peak between 0.9 and 1.1 mrad for simple ionization. A similar peak is seen at ≈ 0.55 mrad for ionization accompanied by either capture by protons or by single stripping of H − . The data for proton impact suggest that all the peaks are related to double ionization of the target. The double-ionization mechanisms will be discussed in terms of their possible contribution to the observed structures.

RTE of hydrogen‐like and lithium‐like ions

Recent results on electron capture with simultaneous excitation of a projectile electron (RTE) are reviewed. These processes are identified by measuring coincidences between two K‐x‐rays and ion with its charge decreased by one unit, for hydrogen‐like or lithium‐like ions, respectively. In the dependence of the cross section on the beam energy it was seen, that this process is resonant and behaves very much like dielectronic recombination. In this work we present and discuss results from measurements of resonant transfer and excitation in collisions of lithium‐like F, hydrogen‐like S, lithium‐, and hydrogen‐like Ge with H2. Emphasis is given to investigating the population of very high n states.

Excitation curve for Auger decay of the (1s2s2p2)3D state of C2+ formed through RTE☆

Abstract The ORNL EN tandem supplied beams of 3.5–9 MeV C 3+ ions which were incident on a differentially pumped He target. Auger electrons emitted by fast C 2+ ions emerged at 10° (lab) w.r.t. the incident ion beam. They were detected using a two stage spectrometer with kinematic refocusing. An excitation curve was obtained for the (1s2s2p 2 ) 3 D state Auger decay to the ground state of C 3+ . The excitation curve peaks at ~ 6 MeV, which strongly supports the notion that the state is formed through resonant transfer and excitation.

Transfer and excitation processes studied in H-like S and Li-like and H-like F colliding with H2

Abstract We have studied transfer and simultaneous excitation by three different experimental techniques. Coincidences between two K X-rays were measured for S15+, as well as coincidences between one K X-ray and the charge-exchanged projectile for Li-like F and projectile Auger electrons for H-like F, in each case colliding with H2. For all three collision system, the measured cross sections are dominated by resonant transfer and excitation (RTE). Also, for the F projectiles, strong contributions from two-electron transfer and excitation (2eTE) were found.