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Wavelength measurements of n=3 to n=2 transitions in neonlike Xe'"^, La' ! ''. Nd 5

The n =2-• n = 1 lines of hydrogenlike and heliumlike uranium have been observed and are being reported for the first time. The spectrum consists of all allowed and forbidden lines. We have done a preliminary energy measurement of these lines with a precision in the (4-12) x 10 ~4 range.

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1s-2p Lyman ␣ transitions in hydrogenic iron Fe 25+ have been observed from a beam-foil source in fourthorder diffraction off ADP 101 and PET 002 crystals, simultaneously with the n =2 to n = 4 Balmer ␤ transitions diffracted in first order. Calibration of the local dispersion relation of the spectrometer using Balmer ␤ lines provides measurements of Lyman ␣ wavelengths. The approach of fitting the full two-dimensional dispersion relation, including other members of Balmer and Lyman series, limits random and systematic correlation of parameters, and reveals a major systematic due to dynamical diffraction depth penetration into a curved crystal. The development of a theory of x-ray diffraction from mosaic crystals was necessary for the accurate interpretation of the experimental data. Photographic theory was also developed in the process of this research. Several systematics are discussed and quantified for the first time for these medium-Z QED comparisons. 2s-1s and 4f-2p satellites are explicitly investigated, and a dominant systematic is uncovered, which is due to the variable location of spectral emission downstream of the beam-foil target. 1s-2p 3/2 , 1s-2p 1/2 iron Lamb shifts are measured to be 35 376± 1900 cm −1 and 35 953± 1800 cm −1 . These agree with but lie higher than theory. This represents a 5.7% measurement of the hydrogenic 1s-2p 1/2 Lamb shift in iron. The technique also reports the iron 2p 3/2 -2p 1/2 fine structure as 171 108 cm −1 ± 180 cm −1 , which represents a 51% measurement of the hydrogenic iron fine-structure Lamb shift, and reports measurements of secondary lines.