Evidence for octupole collectivity in $$^{172}{\mathrm {Pt}}$$172Pt

New isomers in the full seniority scheme of neutron-rich lead isotopes: The role of effective three-body forces

The neutron-rich lead isotopes, up to Pb216, 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 Pb208. © 2012 American Physical Society.