High–resolution measurements of the K-shell spectral lines of hydrogenlike and heliumlike xenon Available to Purchase

With the implementation of a transmission-type curved crystal spectrometer at the Livermore high-energy electron beam ion trap (SuperEBIT) the window on sub-eV level measurements of the ground-state quantum electrodynamics and the two-electron quantum electrodynamics of high-Z ions has been opened. High-resolution spectroscopic measurements of the Kα spectra of hydrogenlike $Xe53+$ and heliumlike $Xe52+$ are presented. The electron-impact excitation cross sections have been determined relative to the radiative recombination cross sections. The electron-impact energy was 112 keV which is about 3.7 times the excitation threshold for the $n=2→1$ transitions. Although the relative uncertainties of the measured electron-impact excitation cross sections range from about 20% to 50%, significant disagreement between the measured and calculated cross section values has been found for one of the helium-like xenon lines. Overall, the comparison between experiment and theory shows that already for xenon $(Z=54)$ the Breit interaction plays a significant part in the collisional excitation process. The measured cross sections for the hydrogenlike transitions are in good agreement with theoretical predictions. Additionally, the $Xe53+Ly−α1$ transition energy has been measured utilizing the Kα emission of neutral cesium and barium for calibration. Surprisingly, the experimental result, $(31279.2±1.5) eV,$ disagrees with the widely accepted theoretically predicted value of $(31283.77±0.09) eV.$ However, this disagreement does not (yet) call for any correction in respect to the theoretical values for the transition energies of the hydrogenlike isoelectronic sequence. It rather emphasizes the need for a re-evaluation of the commonly used x-ray wavelengths table for atomic inner-shell transitions, in particular, for the cesium Kα lines.