Transition energy measurements of the X-ray lines of neon-like europium

We report the measurements of the n = 3 ¡ n = 2 L-shell X-ray transitions of neon-like Eu⁵³⁺. These include all seven allowed electric dipole (E1) transitions, five electric quadrupole (E2) transitions, and one magnetic quadrupole (M2) transition. The measurements were carried out at the EBIT-I electron beam ion trap facility at Livermore using an X-ray calorimeter. The measured values agree with many-body perturbation theory calculations within the experimental uncertainties. This includes the transitions that involve a 2s electron and that are, therefore, strongly affected by quantum electrodynamical effects. (author)