Large odd-even staggering in the very light platinum isotopes from laser spectroscopy

Laser spectroscopy measurements have been carried out on very neutron-deficient platinum isotopes with the COMPLIS experimental set-up on line with the ISOLDE-Booster facility. For the first time, Hg α-decay was exploited to extend the very light platinum chain. Using the 5d96s 3D3→5d96p 3P2 optical transition, hyperfine spectra of 182,181,180,179,178Pt and 183Ptm were recorded for the first time. The variation of the mean square charge radius between these nuclei, the magnetic moments of the odd isotopes and the quadrupole moment of 183Ptm were thus measured. A large deformation change between 183Ptg and 183Ptm, an odd-even staggering of the charge radius and a deformation drop from A=179 are clearly observed. All these results are discussed and compared with microscopic theoretical predictions using Hartree-Fock-Bogolyubov calculations using the Gogny force.