The nucleus 208Pb, with 82 protons and 126 neutrons, is the heaviest known doubly magic nucleus and known stable nucleus. While being spherical in its ground state, 208Pb exhibits strong octupole and quadrupole collectivity arising from the complexity of the nuclear interaction. Additionally, 208Pb carries important information regarding the symmetry energy of the nuclear equation of state, which dictates the behavior of nuclear matter under extreme conditions, such as those found in the inner core of neutron stars. Understanding the properties of 208Pb is thus of paramount importance for numerous fields.

In a recent experimental effort, the properties of the first (3-) and second (2+) excited state of 208Pb have been measured with unprecedented precision, showing a preference for both states to have a large and negative spectroscopic quadrupole moment, indicating a prolate deformation. These measurements challenge the current state-of-the-art theoretical predictions, suggesting the need for refined theoretical approaches to explain the interplay between nuclear magicity and collective motion.

The article was published in Physical Review Letters.