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

The neutron-deficient ${}^{196,198}$Pb 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 $B\left(E2\right)={18.2}_{-4.1}^{+4.8}$ W.u. and $B\left(E2\right)={13.1}_{-3.5}^{+4.9}$ W.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. (paper)