The impact of nuclear deformation can been seen in the systematics of nuclear charge radii, with radii generally expanding with increasing deformation. In this Letter, we present a detailed analysis of the precise relationship between nuclear quadrupole deformation and the nuclear size. Our approach combines the first measurements of the changes in the mean-square charge radii of well-deformed palladium isotopes between $A=98$ and $A=118$ with nuclear density functional calculations using Fayans functionals, specifically Fy(std) and $\mathrm{Fy}(\mathrm{\Delta }r,\mathrm{HFB})$, and the UNEDF2 functional. The changes in mean-square charge radii are extracted from collinear laser spectroscopy measurements on the $4d^{9}5s{{}^{3}D}_3\to 4d^{9}5p{}^3{P}_2$ atomic transition. The analysis of the Fayans functional calculations reveals a clear link between a good reproduction of the charge radii for the neutron-rich Pd isotopes and the overestimated odd-even staggering: Both aspects can be attributed to the strength of the pairing correlations in the particular functional which we employ.

• Received 29 October 2021
• Revised 1 February 2022
• Accepted 10 March 2022

DOI:https://doi.org/10.1103/PhysRevLett.128.152501