Ground-state excitation of heavy highly-charged ions

Abstract

We have studied the excitation of H-like and He-like uranium (U91+ and U90+) in relativistic collisions with gaseous targets by observing the subsequent x-ray emission. The experiment was conducted at the ESR storage ring of the GSI accelerator facility in Darmstadt, Germany. The measurements were performed with a newly developed multi-phase target at different collision energies. This enabled us to explore the proton (nucleus) impact excitation as well as the electron impact excitation processes in the relativistic collisions. The large fine-structure splitting in uranium allowed us to unambiguously resolve excitation to different L-shell levels. Moreover, information about the population of different magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The experimental results are compared with calculations performed within the relativistic framework including excitation mechanisms due to both protons (nucleus) and electrons.

Angular Distribution of Characteristic Radiation Following the Excitation of He-Like Uranium in Relativistic Collisions

“…In the current paper, we present an experimental and theoretical study of the angular distributions for the Kα radiation produced by K-shell excitation of He-like uranium in relativistic collisions with H 2 and Ar targets. This work is an extension of our previous studies for H-and He-like uranium [25,28]. In contrast to the case of H-like uranium [28], here we demonstrate for the first time a clear role of the EIE process in the angular distributions of the Kα radiation for the excitation of He-like uranium in collisions with different targets.…”

“…In [28], we have addressed angular differential cross sections for the Lyman-α 1 transition (2p 3/2 → 1s 1/2 ) produced by the excitation of H-like uranium in collisions with H 2 and N 2 targets. The angular distributions provide access to the characteristics of magnetic sub-level population for the 2p 3/2 state and the corresponding alignment, serving as a stringent test of the underlying theoretical approaches.…”

“…The angular distributions provide access to the characteristics of magnetic sub-level population for the 2p 3/2 state and the corresponding alignment, serving as a stringent test of the underlying theoretical approaches. In [28], it has been found that in contrast to the ratios of the characteristic line intensities, where EIE plays a prominent role for an H 2 target, the corresponding angular distributions are relatively insignificantly affected by the EIE process and thus its influence could not be identified experimentally taking into account the corresponding uncertainties.…”

Electron- and proton-impact excitation of heliumlike uranium in relativistic collisions

“…(1) to the angular distribution of the Kα 1 /Kα 2 intensity ratios. This is in contrast to the H-like case where it was possible to extract directly the alignment parameter for the 2p 3/2 state from the angular distribution of the Lyα 1 line [18,29]. The parameter R gives the Kα 1 /Kα 2 intensity ratio at the "magic angle," i.e., the angle for which the angle-dependent part of Eq.…”

Mechanism of dominance of the Breit interaction in dielectronic recombination

“…For such a dynamical process, the Breit interaction directly competes with the electronelectron Coulomb interaction and in most cases, the Breit interaction may modify the process quantitatively not qualitatively. The Breit interaction plays an important role for high energy electrons colliding with a highly charged ion [9,10,11] as well.…”