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

Abstract

Abstract.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 twoelectron quantum electrodynamics of high-Z ions has been opened. High-resolution spectroscopic measurements of the Kcr 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 heliumlike 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-or transition energy has been measured utilizing the Kcr emission of neutral cesium and barium for calibration. Surprisingly, the experimental result, (31279.2 f. 1.5) eV, disagrees with the widely accepted theoretically predicted value of (31283.77 f 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 reevaluation of the commonly used x-ray wavelengths table for atomic inner-hell transitions, in particular, for the cesium KQ lines. r) Email: widmannl@llnl.gov. 2, Present address:

Electron-impact excitation cross-section measurements at EBITs from 1986 to 2006

“…One measurement in this group is of He-like Xe using SuperEBIT [21]. Generally speaking, we can divide the measurements into two groups.…”

“…Crystal spectrometers employed in cross-section measurements either employed reflective crystals (mostly flat or cylindrically curved) [17-20, 22-24, 26] or transmissive crystals [21]. The resolving power of the spectrometers ranged from many hundreds to a few thousand.…”

“…EIE cross sections for high-Z ions were first measured by Widmann et al [21]. Their measurements were performed on SuperEBIT [34] at electron-beam energies of 112 keV.…”

Comment on electron-impact excitation cross section measurements for He-like xenon

“…In both refs. [1] and [3], the authors find that the experimental EIE cross-sections derived from the Xe spectrum agree well with relativistic distortedwave (DW) calculations as long as the Breit interaction is included. They conclude: "This was the first experimental demonstration of this effect, and it clearly shows for the resonance line w and the intercombination line y, where inclusion of the generalized Breit interaction changes the results by a factor of two.…”

High-resolution spectroscopy of K-shell praseodymium with a high-energy microcalorimeter

“…But the low intrinsic resolving power of the germanium detector did not allow for as high a precision result as the crystal spectrometers did for the lower Z ion measurements. The later measurement by Widmann et al [7], tried to remedy this problem by using a hybrid instrument of a transmission crystal spectrometer and a germanium detector on the SuperEBIT electron beam ion trap and obtained results of higher precision. However, the hybrid method suffered from a low count rate and was extremely time consuming.…”