Influence of theN=50shell closure on mean square charge radii of strontium

Isotope shifts of the stable strontium isotopes $^{84}\mathrm{Sr}$, $^{86}\mathrm{Sr}$, $^{87}\mathrm{Sr}$, and $^{88}\mathrm{Sr}$ and the radioactive isotopes $^{89}\mathrm{Sr}$ and $^{90}\mathrm{Sr}$ have been measured using laser spectroscopy on collimated atomic beams. The changes in mean square charge radii extracted from the isotope shifts show a pronounced shell effect at the closed neutron shell N=50. The experimental data are compared with the predictions of the droplet model and Hartree-Fock plus BCS calculations. The analysis suggests that the changes in mean square charge radii are due to a change in size, a change in the predominantly dynamic deformation, and a change in the diffuseness of the nuclear charge distribution.