Isotope shifts and nuclear charge radii of krypton isotopes across the N=50 shell closure

Abstract

Optical isotope shifts have been measured in the 5s[3/2${]}_{2}^{0}$-5p[3/2${]}_{2}$ transition in atomic krypton (\ensuremath{\lambda}=760 nm) using collinear-fast-beam laser spectroscopy. Isotope shifts were determined for the short-lived neutron-rich isotopes $^{88}\mathrm{Kr}$ and $^{90}\mathrm{Kr}$, as well as for all the stable isotopes between A=78 and 86, thus extending the data in this element, for the first time, beyond the N=50 shell closure. The deduced changes in the nuclear charge radii show a decrease of the charge radius with increasing neutron number below N=50, and a much more rapid increase above it. A preliminary interpretation of the results is given in terms of the droplet model.