A three-configuration mixing calculation is presented in the context of the Interacting Boson Model (IBM1), with the aim to describe recently observed collective bands built on low-lying 0⁺ states in the neutron-deficient lead isotopes. Possible effects on the nuclear binding energy are addressed, caused by mixing of these low-lying 0⁺ intruder states into the ground state, and a new method is described in order to provide a consistent description of both ground-state and excited-state properties.

PACS numbers: 21.10.-k, 21.10.Dr, 21.60.Fw, 27.70.+q