New spectroscopic information on Tl211,213 : A changing structure beyond the N=126 shell closure

The neutron-rich isotopes $^{211,213}\mathrm{Tl}$, beyond the $N=126$ shell closure, have been studied for the first time in isomer $\ensuremath{\gamma}$-ray decay, exploiting the fragmentation of a primary uranium beam at the Fragment Separator-Rare Isotopes Investigation at GSI setup. The observed isomeric states in $^{211,213}\mathrm{Tl}$ show a deviation from the seniority-like scheme of $^{209}\mathrm{Tl}$. The possible interpretation of the data is discussed on the basis of energy-level systematics and shell-model calculations.