100 Years of Nuclear Isomers

Nuclei in the vicinity of doubly-magic ones often exhibit isomeric states arisen due to the low energies and/or high multipolarities of the gamma rays depopulating them. Around ${}^{208}$Pb these long-lived states often decay by electric octupole (E3) transitions. Their transition strength give information about their nature. In this region these can be collective, explained by the large number of $\mathrm{\Delta }l$=$\mathrm{\Delta }j$=3 orbital pairs across Z=82 and N=126, forming a vibrational phonon with B(E3)~35 W.u. at ~2.6 MeV. Or they can be of single-particle nature, connected to the presence of a non-natural parity high $j$ orbitals in all four shells around ${}^{208}$Pb. Alternatively, they can be mixed.
This contribution will discuss the structure of nuclei in the vicinity of ${}^{208}$Pb, with emphasis on isomeric states and the role of octupole collectivity.