The magnetic dipole moments and changes in mean-square charge radii of the neutron-rich 218m,219,229,231Fr isotopes were measured with the newly installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at the On-Line Isotope Mass Separator (ISOLDE), CERN, probing the 7s2S1/2 to 8p2P3/2 atomic transition. The δr2A,221 values for 218m,219Fr and 229,231Fr follow the observed increasing slope of the charge radii beyond N=126. The charge radii odd-even staggering in this neutron-rich region is discussed, showing that 220Fr has a weakly inverted odd-even staggering while 228Fr has normal staggering. This suggests that both isotopes reside at the borders of a region of inverted staggering, which has been associated with reflection-asymmetric shapes. The g(219Fr)=+0.69(1) value supports a π1h9/2 shell-model configuration for the ground state. The g(229,231Fr) values support the tentative Iπ(229,231Fr)=(1/ 2+) spin and point to a πs1/2-1 intruder ground-state configuration.
ASJC Scopus subject areas
- Nuclear and High Energy Physics