Relativistic calculations of the x-ray emission following the Xe-Bi83+^{83+} collision

We study the x-ray emission following the collision of a Bi$^{83+}$ ion with a neutral Xe atom at the projectile energy 70 MeV/u. The collisional and post-collisional processes are treated separately. The probabilities of various many-electron processes at the collision are calculated within a relativistic independent electron model using the coupled-channel approach with atomic-like Dirac-Fock-Sturm orbitals. The analysis of the post-collisional processes resulting in the x-ray emission is based on the fluorescence yields, the radiation and Auger decay rates, and allows to derive intensities of the x-ray emission and compare them with experimental data. A reasonable agreement between the theoretical results and the recent experimental data is observed. The role of the relativistic effects is investigated.Comment: 11 figures, 2 table

Magnetic Sublevel Population and Alignment for the Excitation of H- and He-like Uranium in Relativistic Collisions

We have measured the alignment of the L-shell magnetic-substates following the K-shell excitation of hydrogen- and helium-like uranium in relativistic collisions with a low-Z gaseous target. Within this experiment the population distribution for the L-shell magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The results show a very distinctive behavior for the H- and He-like heavy systems. In particular for $K \rightarrow L$ excitation of He-like uranium, a considerable alignment of the L-shell levels was observed. A comparison of our experimental findings with recent rigorous relativistic predictions provides a good qualitative and a reasonable quantitative agreement, emphasizing the importance of the magnetic-interaction and many-body effects in the strong-field domain of high-Z ions

Polarization transfer in Rayleigh scattering of hard x-rays

Wereport on the first elastic hard x-ray scattering experiment where the linear polarizationcharacteristics of both the incident and the scattered radiation were observed. Rayleigh scattering wasinvestigated in a relativistic regime by using a high-Z target material, namely gold, and a photon energyof 175keV. Although the incident synchrotron radiation was nearly 100% linearly polarized, at ascattering angle of q = 90we observed a strong depolarization for the scattered photonswith adegree of linear polarization of +0.27% 0.12%only. This finding agreeswith second-orderquantum electrodynamics calculations of Rayleigh scattering, when taking into account a smallpolarization impurity of the incident photon beam which was determined to be close to 98%. Thelatter value was obtained independently from the elastic scattering by analyzing photons that wereCompton-scattered in the target. Moreover, our results indicate that when relying on state-of-the-arttheory, Rayleigh scattering could provide a very accurate method to diagnose polarization impuritiesin a broad region of hard x-ray energies

Electronic temperatures, densities and plasma X-ray emission of a 14.5 GHz Electron-Cyclotron Resonance Ion Source

We have performed a systematic study of the Bremsstrahlung emission from the electrons in the plasma of a commercial 14.5 GHz Electron-Cyclotron Resonance Ion Source. The electronic spectral temperature and the product of ionic and electronic densities of the plasma are measured by analyzing the Bremsstrahlung spectra recorded for several rare gases (Ar, Kr, Xe) as a function of the injected power. Within our uncertainty, we find an average temperature of ? 48 keV above 100W, with a weak dependency on the injected power and gas composition. Charge state distributions of extracted ion beams have been determined as well, providing a way to disentangle the ionic density from the electronic density. Moreover X-ray emission from highly charged argon ions in the plasma has been observed with a high-resolution mosaic crystal spectrometer, demonstrating the feasibility for high-precision measurements of transition energies of highly charged ions, in particular of the magnetic dipole (M1) transition of He-like of argon ions

Isotope shift in the dielectronic recombination of three-electron ^{A}Nd^{57+}

Isotope shifts in dielectronic recombination spectra were studied for Li-like ^{A}Nd^{57+} ions with A=142 and A=150. From the displacement of resonance positions energy shifts \delta E^{142,150}(2s-2p_1/2)= 40.2(3)(6) meV (stat)(sys)) and \delta E^{142,150}(2s-2p_3/2) = 42.3(12)(20) meV of 2s-2p_j transitions were deduced. An evaluation of these values within a full QED treatment yields a change in the mean-square charge radius of ^{142,150}\delta = -1.36(1)(3) fm^2. The approach is conceptually new and combines the advantage of a simple atomic structure with high sensitivity to nuclear size.Comment: 10 pages, 3 figures, accepted for publication in Physical Review Letter