Collectivity in 196,198Pb isotopes probed in Coulomb-excitation experiments at REX-ISOLDE

The neutron-deficient 196,198Pb isotopes have been studied in Coulomb-excitation experiments employing the Miniball γ-ray spectrometer and radioactive ion beams from the REX-ISOLDE post-accelerator at CERN. The reduced transition probabilities of the first excited 2+ states in 196Pb and 198Pb nuclei have been measured for the first time. Values of B (E2) =18.2 -4.1 +4.8 W.u. and B( E2) =13.1 -3.5 +4.9W.u., were obtained, respectively. The experiment sheds light on the development of collectivity when moving from the regime governed by the generalised seniority scheme to a region, where intruding structures, associated with different deformed shapes, start to come down in energy and approach the spherical ground state.