Mean square charge radii of radium isotopes and octupole deformation in the 220–228Ra region

Abstract

The first investigation of isotope shifts in both the atomic and ionic resonance lines of radium has been carried out using the technique of on-line collinear fast-beam laser spectroscopy at the ISOLDE facility at CERN. The measurements cover 19 isotopes in the mass range 208⩽A⩽232 with half-lives between 23 ms and 1600 y. The differences in the nuclear mean square charge radii δ〈r2〉 have been evaluated and - together with earlier published spins and moments from the hyperfine structure - related to nuclear deformation. In particular the inversion of the odd-even staggering effect for the isotopes 221Ra, 223Ra and 225Ra can be interpreted by the presence of octupole instability and adds weight to the concept of near-stable octupole deformation in the odd-A isotopes which already explained their spins and magnetic moments.