Isotope shift factors for the Cd+ 5s 2S1/2 → 5p 2P3/2 transition and determination of Cd nuclear charge radii

The accuracy of atomic isotope shift factors limits the extraction of nuclear charge radii from isotope shift measurements because determining these factors is experimentally and theoretically challenging. Here, the isotope shift of the Cd + 5s S-2(1/2) -> 5p P-2(3/2) transition is measured precisely using laser-induced fluorescence from a sympathetically cooled large Cd+ ion crystal. A King-plot analysis is performed based on the new measurement to obtain accurate atomic field shift F and mass shift K factors that have been cross-checked by state-of-the-art configuration interaction plus many-body perturbation theory. The nuclear charge radii (R-ch) of Cd100-130 extracted using these F and K values demonstrate a near fivefold precision increase in the neutron-rich region. This work proves that accurate extraction of R-ch from isotope shifts is possible. New R-ch values reveal hidden discrepancies with previous density functional predictions in the neutron-rich region and pose strong challenges to advancements in nuclear models.