Quantum Electrodynamics in Strong Electromagnetic Fields: Substate Resolved $\mathrm{K}α$ Transition Energies in Heliumlike Uranium

Author(s): Ph. Pfäfflein et al. Using novel metallic magnetic calorimeter detectors at the CRYRING@ESR, we recorded x-ray spectra of stored and electron cooled heliumlike uranium (${\mathrm{U}}^{90+}$) with an unmatched spectral resolution of close to 90 eV. This allowed for an accurate determination of the energies of all four co… [Phys. Rev. Lett. 134, 153001] Published Mon Apr 14, 2025