The neutron-rich lead isotopes, up to ${}^{216}\mathrm{Pb}$, have been studied for the first time, exploiting the fragmentation of a primary uranium beam at the FRS-RISING setup at GSI. The observed isomeric states exhibit electromagnetic transition strengths which deviate from state-of-the-art shell-model calculations. It is shown that their complete description demands the introduction of effective three-body interactions and two-body transition operators in the conventional neutron valence space beyond ${}^{208}\mathrm{Pb}$.

• Received 9 February 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.162502