Doubly magic Pb208 : High-spin states, isomers, and E3 collectivity in the yrast decay

The nucleus ${}^{208}$Pb provides an iconic test of the nuclear shell model because its 82 protons and 126 neutrons are both magic numbers. When excited levels are discovered and characterized, this nucleus provides a means to investigate the mechanisms responsible for the generation of angular momentum and, ultimately, for the development of collectivity. This experiment is a tour de force that reveals extensive new information on ${}^{208}$Pb about high-angular-momentum states, isomeric states, and collective states of octupole nature; thus it serves as a showcase for shell-model descriptions. Many of the states explored show good overall agreement with theory, but others at the highest energies reveal discrepancies, pointing to the need for improved calculations. Above the highest-lying ${28}^{-}$ isomer $\ensuremath{\gamma}$ transitions arising from yet higher spin levels could be identified in two separate experiments as displayed in the figure.