We perform ab initio QED calculations of energy levels for the n = 1 and n = 2 states of He-like ions with the nuclear charge in the range Z = 12-100. The complete set of two-electron QED corrections is evaluated to all orders in the parameter αZ. Uncalculated contributions to energy levels come through orders α 3 (αZ) 2 , α 2 (αZ) 7 , and higher. The calculation presented is the first treatment for excited states of He-like ions complete through order α 2 (αZ) 4 . A significant improvement in accuracy of theoretical predictions is achieved, especially in the high-Z region.
The ground-state hyperfine splitting values of high-Z hydrogenlike ions are calculated. The relativistic, nuclear, and QED corrections are taken into account. The nuclear magnetization distribution correction ͑the Bohr-Weisskopf effect͒ is evaluated within the single-particle model with the g S factor chosen to yield the observed nuclear moment. An additional contribution caused by the nuclear-spin-orbit interaction is included in the calculation of the Bohr-Weisskopf effect. It is found that the theoretical value of the wavelength of the transition between the hyperfine-splitting components in 165 Ho 66ϩ is in good agreement with experiment.
The relativistic nuclear recoil corrections to the energy levels of low-laying states of hydrogen-like and high Z lithium-like atoms in all orders in αZ are calculated. The calculations are carried out using the B-spline method for the Dirac equation. For low Z the results of the calculation are in good agreement with the αZ -expansion results. It is found that the nuclear recoil contribution, additional to the Salpeter's one, to the Lamb shift (n = 2) of hydrogen is −1.32(6) kHz. The total nuclear recoil correction to the energy of the (1s) 2 2p 1 2 − (1s) 2 2s transition in lithium-like uranium constitutes −0.07 eV and is largely made up of QED contributions.PACS number(s): 12.20.Ds, 31.30.Jv
A possibility for investigations of quantum electrodynamics (QED) in experiments on the hyperfine splitting in heavy ions is examined. It is found that QED effects can be probed on the level of a few percent in a specific difference of the hyperfine splitting values in hydrogenlike and lithiumlike bismuth. This could provide a test of QED in the strongest electric field available at present for experimental study.
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