Using x-ray diffraction and beam-foil spectroscopy, we have determined precise wavelengths for Lyman ␣ 1 and Lyman ␣ 2 in hydrogenic germanium of 1.166 993 8 Ϯ 33Ϯ 169 and 1.172 433 6 Ϯ 39Ϯ 170 Å. Hydrogenic germanium Ge 31+ 1s-2p 3/2 and 1s-2p 1/2 Lamb shifts are measured to be 66 080Ϯ 237Ϯ 1121 and 67 169Ϯ 281Ϯ 1237 cm −1 , respectively. This 14 ppm measurement of the wavelengths thus provides a 1.8% measurement of the 2p-1s Lamb shift and is an improvement by a factor of 3 over previous work. Fitting the full two-dimensional dispersion relation, including Balmer and Lyman series, limits random and systematic correlation of parameters. Dominant systematics are due to diffraction parameters including crystal thickness and alignment, differential Doppler shifts due to the variable location of spectral emission downstream of the beam-foil target, and dielectronic, 2s-1s, and 4f-2p satellites. Models developed are applicable to all relativistic plasma modeling in beam-foil spectroscopy at accelerators. The technique also reports the germanium 2p 3/2 -2p 1/2 fine structure as 397 617Ϯ 251Ϯ 512 cm −1 , representing a 0.14% measurement of the fine structure and a 71% measurement of the QED contribution to the hydrogenic germanium fine structure, an improvement of a factor of 6 over previous work. We also report a precise measurement of heliumlike resonances and fine structure.
The n =3 to 2 transitions in Ne-like, Na-like, and Mg-like bismuth were measured on the UNI-LAC accelerator at the Gesellschaft fur Schwerionenforschung in Darmstadt, West Germany, using the Lawrence Livermore National Laboratory high-resolution double-crystal spectrometer. The measurements cover the region 10 -14 keV with precisions of the order of 100 ppm and include electric-dipole and quadrupole transitions. Theoretical multiconfigurational Dirac-Fock calculations were made for the Ne-like system and compared to the experiment. The data exhibit energy shifts of 1.5-2.5 eV from the theory, confirming trends previously observed in tokamak experiments. The Na-like and Mg-like results are compared with unresolved transition array calculations.
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