New spectroscopic information on ${}^{211,213}\mathrm{Tl}$: 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 $\gamma$-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.

Figure 1

Reaction fragment identification plot at the final focal plane of the FRS. The fragments of interest have been circled, as well as some neighboring nuclei to provide a reference.

Figure 2

Gamma-ray spectrum from the decay of the isomeric state in ${}^{211}\mathrm{Tl}$. The spectrum has been taken with a time window 0.12–3.00 $\mu \mathrm{s}$ after implantation.

Figure 3

Gamma-ray spectrum in prompt coincidence with the 144-keV transition from the decay from the isomeric state in ${}^{211}\mathrm{Tl}$.

Figure 4

Time distribution for the 144-keV transition in ${}^{211}\mathrm{Tl}$.

Figure 5

Gamma-ray spectrum from the decay of the isomeric state in ${}^{213}\mathrm{Tl}$. The spectrum has been obtained by selecting a time window of 0.12–20 $\mu \mathrm{s}$ after implantation.

Figure 6

Gamma-ray spectra in prompt coincidence with the 380- and 698-keV transitions observed in the decay of isomeric states in ${}^{213}\mathrm{Tl}$, with gates on the two transitions following the isomers.

Figure 7

Time distribution of the 380-keV transition in ${}^{213}\mathrm{Tl}$.

Figure 8

Time distribution of the 698-keV transition in ${}^{213}\mathrm{Tl}$.

Figure 9

Experimental [1] and calculated level scheme of ${}^{209}\mathrm{Tl}$. The experimental $5/2^{+}$ state is reported in Ref. [5]. The low-energy transitions depopulating the isomer are taken from the same reference.

Figure 10

A tentative proposal for experimental level scheme of ${}^{211}\mathrm{Tl}$ compared with shell-model calculations performed with the interaction and valence space described in the text.

Figure 11

Shell-model calculations for ${}^{213}\mathrm{Tl}$, performed with the interaction and valence space from Ref. [1].