New spectroscopic information on Tl 211,213: A changing structure beyond the N=126 shell closure

The neutron-rich isotopes Tl211,213, beyond the N=126 shell closure, have been studied for the first time in isomer γ-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 Tl211,213 show a deviation from the seniority-like scheme of Tl209. The possible interpretation of the data is discussed on the basis of energy-level systematics and shell-model calculations.