Nuclear charge radii of potassium isotopes beyond N=28

We report on the measurement of optical isotope shifts for K-38,K-39,K-42,K-44,K-46-51 relative to K-47 from which changes in the nuclear mean square charge radii across the N = 28 shell closure are deduced. The investigation was carried out by bunched-beam collinear laser spectroscopy at the CERN-ISOLDE radioactive ion-beam facility. Mean square charge radii are now known from K-37 to K-51, covering all vf(7/2)-shell as well as all vp(3/2)-shell nuclei. These measurements, in conjunction with those of Ca, Cr, Mn and Fe, provide a first insight into the Z dependence of the evolution of nuclear size above the shell closure at N = 28. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (hup://creativecommons,org/licenses/by/3.0/).