Measurement of the 1s Lamb shift in hydrogenlike nickel

The wavelength of the 2${\mathit{p}}_{3/2}$→1${\mathit{s}}_{1/2}$ transition in hydrogenlike ${\mathrm{Ni}}^{27+}$ has been measured with an accuracy of 13 ppm. Bare ${\mathrm{Ni}}^{28+}$ ions of 11.4 MeV/amu as emerging from a carbon stripper foil were decelerated to 8.4, 6.7, 5.2, and 3.1 MeV/amu and dressed in a thin target gas by electron capture. The x rays were measured with a crystal spectrometer in Johann geometry employing a position-sensitive x-ray detector. The 1s Lamb shift in hydrogenlike nickel has been found to be 5.07±0.10 eV in good agreement with theory.