Effects of Configuration Interaction on the Alignment of Beryllium-Like Ions

The radiative electron capture into (initially) lithium-like ions is studied within the framework of the density matrix approach. Special attention is paid to the magnetic sublevel population of the residual ionic states which is described by a set of alignment parameters. Detailed calculations of these parameters have been performed for the capture into the 1s2 2s 3d3/2 Jf2 level of high-Z ions along the beryllium isoelectronic sequence. We devote special attention to the modifications in the many-electron case as opposed to singleelectron systems. The electron correlation leads to an enhancement of the alignment, which becomes more pronounced as the nuclear charge decreases and the electron-electron interaction gains in strength as compared to the electron-nucleus interaction

K α₁ Radiation from Heavy, Heliumlike Ions Produced in Relativistic Collisions

Bound-state transitions in few-electron, heavy ions following radiative electron capture are studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock approach. Special attention is paid to the K α1 (1 s1/2 2 p3/2 1.3PJ=1,2→1s21/2 1SJ=0) radiative decay of heliumlike uranium U90+ projectiles. This decay has recently been observed at the GSI facility in Darmstadt, giving rise to a surprisingly isotropic angular distribution, which is inconsistent with previous experiments and calculations based on a one-particle model. We show that the unexpected isotropy essentially results from the mutual cancellation of the angular distributions of the 1P1 → 1S0 electric dipole and 3P2 → 1S0 magnetic quadrupole transitions, both of which contribute to the K α1 radiation. Detailed computations on the anisotropy of the K α1 radiation have been carried out for a wide range of projectile energies and are compared to available experimental data

Angular and Polarization Analysis of X-Rays Emitted from Highly-Charged, Few-Electron Ions

The recent theoretical progress in studying the x-ray emission from highly-charged, few-electron ions is reviewed. These case studies show that relativistic, high-Z ions provide a unique tool for better understanding the interplay between the electron-photon and electron-electron interactions in strong fields. Most naturally, this interplay is probed by the radiative capture of a (quasi-) free electron into the bound states of projectile ions, and by varying the charge state and the energy of the projectiles. For the capture into initially hydrogen-and lithium-like ions, here we summarize the recent results for the angular distribution and polarization of the recombination photons as well as the subsequent Kα emission, if the electron is captured into an excited state of the ion

Radiative Electron Capture into High- Z Few-Electron Ions: Alignment of the Excited Ionic States

We lay out a unified formalism for the description of radiative electron capture into excited states of heavy, few-electron ions and their subsequent decay, including a full account of many-electron effects and higher-order multipoles of the radiation field. In particular, the density-matrix theory is applied to explore the magnetic sublevel population of the residual ions, as described in terms of alignment parameters. For the electron capture into the initially hydrogenlike U91+ and lithiumlike U89+ uranium projectiles, the alignment parameters are calculated, within the multiconfiguration Dirac-Fock approach, as a function of the collision energy and for different ionic states. From these calculations, we find that the many-electron interactions may result in a small enhancement of the alignment, and that this effect becomes more pronounced for highly excited levels

Isotope shifts of the 2p3/2p_{3/2}-2p1/2p_{1/2} transition in B-like ions

Isotope shifts of the 2$p_{3/2}$-2$p_{1/2}$ transition in B-like ions are evaluated for a wide range of the nuclear charge number: Z=8-92. The calculations of the relativistic nuclear recoil and nuclear size effects are performed using a large scale configuration-interaction Dirac-Fock-Sturm method. The corresponding QED corrections are also taken into account. The results of the calculations are compared with the theoretical values obtained with other methods. The accuracy of the isotope shifts of the 2$p_{3/2}$-2$p_{1/2}$ transition in B-like ions is significantly improved.Comment: arXiv admin note: text overlap with arXiv:1410.707

Alignment of Heavy Few-Electron Ions Following Excitation by Relativistic Coulomb Collisions

The Coulomb excitation of highly charged few-electron ions in relativistic collisions with protons and low- Z atoms is studied within the framework of first-order perturbation theory and the multiconfiguration Dirac-Fock method. Apart from the computation of the total excitation cross sections, a detailed theoretical analysis has been performed for the magnetic sublevel population of the residual ions. To describe this population, general expressions are derived for the alignment parameters of the excited states of the ions, taking into account the relativistic and many-electron effects. Calculations are performed for the K→L and K→M excitation of helium- and lithiumlike uranium ions and for a wide range of projectile energies. It is shown that the alignment of heavy few-electron ions is sensitive to relativistic and magnetic-interaction effects and, hence, to the collision energies of the projectiles. The theoretical predictions are discussed in the context of recent measurements on the Coulomb excitation of heliumlike uranium U90+ ions which were recently performed at the GSI storage ring in Darmstadt

Electron Loss from 1.4-MeV / u U\u3csup\u3e4,6,10+\u3c/sup\u3e Ions Colliding with Ne, N₂, and Ar Targets

Absolute, total, single- and multiple-electron-loss cross sections are measured for 1.4-MeV / u U4,6,10+ ions colliding with neon and argon atoms and nitrogen molecules. It is found that the cross sections all have the same dependence on the number of electrons lost and that multiplying the cross sections by the initial number of electrons in the 6s, 6p, and 5f shells yields good agreement between the different projectiles. By combining the present data with previous measurements made at the same velocity, it is shown that the scaled cross sections slowly decrease in magnitude for incoming charge states between 1 and 10, whereas the cross sections for higher-charge-state ions fall off much more rapidly

Isotope Shift in the Dielectronic Recombination of Three-electron \u3csup\u3eA\u3c/sup\u3eNd⁵⁷⁺

Isotope shifts in dielectronic recombination spectra were studied for Li-like ANd57+ ions with A = 142 and A = 150. From the displacement of resonance positions energy shifts δE142 150(2s-2p1/2) = 40.2(3)(6) meV [(stat)(sys)] and δE142 150(2s - 2p3/2) = 42.3(12)(20)meV of 2s - 2pj transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of 142 150δ⟨ r2⟩ = -1.36(1)(3) fm2. The approach is conceptually new and combines the advantage of a simple atomic structure with high sensitivity to nuclear size

Technique for Resolving Low-lying Isomers in the Experimental Storage Ring (ESR) and the Occurrence of an Isomeric State in 192Re

A recent experiment using projectile fragmentation of a 197Au beam on a 9Be target, combined with the fragment recoil separator and experimental storage ring at ring at GSI, has uncovered an isomeric state in 192Re at 267(10) keV with a half-life of ∼6