Early onset of ground-state deformation in the neutron-deficient polonium isotopes

Abstract

In-source resonant ionization laser spectroscopy of the even-$A$ polonium isotopes ${}^{192-210,216,218}$Po has been performed using the $6p^{3}7s$ ${}^5{S}_2$ to $6p^{3}7p$ ${}^5{P}_2$ ($\hat{I}»=843.38$ nm) transition in the polonium atom (Po-I) at the CERN ISOLDE facility. The comparison of the measured isotope shifts in ${}^{200-210}$Po with a previous data set allows to test for the first time recent large-scale atomic calculations that are essential to extract the changes in the mean-square charge radius of the atomic nucleus. When going to lighter masses, a surprisingly large and early departure from sphericity is observed, which is only partly reproduced by Beyond Mean Field calculations.

As submitted to PRL