Intruder Bands And Configuration Mixing In The Lead Isotopes

A three-configuration mixing calculation is performed, for the first time, in the context of the interacting boson model with the aim to describe recently observed collective bands built on low-lying 0(+) states in neutron-deficient lead isotopes. The configurations that are included correspond to the regular, spherical states as well as two-particle two-hole and four-particle four-hole excitations across the Z = 82 shell gap. The latter two configurations may be associated with oblate and prolate shapes, respectively.