Identification of excited states in ${}_{52}{}^{107}\mathrm{Te}_{55}$

Excited states in the extremely neutron-deficient nucleus ${}^{107}\mathrm{Te}$ have been identified from two separate experiments using the recoil-decay tagging technique. Two connected structures were observed on the basis of $\gamma \gamma$-coincidence relations and tentatively assigned as built on the mixed-parentage $\nu g_{7/2}{d}_{5/2}$ and $\nu h_{11/2}$ intruder configurations. The observed structures were compared with large-scale shell-model calculations and total Routhian surface calculations. Collective behavior was discovered to persist in the $\nu h_{11/2}$ band of ${}^{107}\mathrm{Te}$ which highlights the shape-polarizing effect of a single valence neutron occupying the $h_{11/2}$ intruder orbit as the $N=50$ shell closure is approached.

Figure 1

(a) Recoil-correlated $\gamma$-ray energy spectrum from the RITU experiment, dominated by transitions in the strongest three-proton evaporation reaction channel, ${}^{109}\mathrm{Sb}$ [35]. (b) As in panel (a), with additional selection on the characteristic $\alpha$-decay energy of ${}^{107}\mathrm{Te}$. Contamination lines arising from ${}^{109}\mathrm{Sb}$ are indicated by filled squares. (c) Recoil-correlated $\gamma$-ray energy spectrum from the MARA experiment. (d) RDT $\gamma$-ray spectrum for ${}^{107}\mathrm{Te}$. The energy calibration of the germanium detectors was performed offline using in-beam $\gamma$ rays of ${}^{109}\mathrm{Sb}$ for both experiments, indicated by solid circles. The black (and red) dashed lines are drawn to guide the eye and illustrate the energy consistency in the calibration (and $\gamma$ rays for ${}^{107}\mathrm{Te}$) from the two experiments.

Figure 2

Coincidence $\gamma$-ray spectra obtained by gating on the (a) 632-keV, (b) 669-keV, (c) 573-keV, (d) 960-keV, (e) 723-keV, and (f) 677-keV transitions. Panel (g) shows a sum of gates on some transitions in the $\gamma \gamma$ matrix, specifically the 980-, 750-, or 669-keV transitions.

Figure 3

A tentative level scheme deduced for ${}^{107}\mathrm{Te}$ from this work. The transition energies are given in keV.

Figure 4

Excitation energies of states in the yrast $\nu h_{11/2}$ bands in the odd-$A$ tellurium isotopes, relative to the respective $11/2^{-}$ bandheads. The data for heavier Te isotopes are taken from Refs. [3, 14, 36] and the data for ${}^{107}\mathrm{Te}$ are derived from the present work. The dashed lines are drawn to show the energy evolution as the number of neutrons changes.

Figure 5

Energy ratios plotted versus $N$ for even- and odd-$A{}_{52}\mathrm{Te}$ isotopes in the mass region $A⩽119$. The data are taken from the present work and Refs. [2, 3, 5, 14, 15, 18, 36].

Figure 6

Experimental positive-parity levels in ${}^{107}\mathrm{Te}$ derived from this work in comparison with LSSM calculations. See text for details.

Figure 7

Excitation energies of states in the yrast $\nu h_{11/2}$ band of ${}^{107}\mathrm{Te}$ and the ground-state bands of the neighboring even-even ${}^{106}\mathrm{Te}$ [2] and ${}^{108}\mathrm{Te}$ [5] isotopes in comparison with the shell-model calculations. See text for details.

Figure 8

Calculated TRSs for ground-state bands of ${}^{106,108}\mathrm{Te}$ and for positive-parity and negative-parity bands of ${}^{107,109}\mathrm{Te}$ at a rotational frequency of $\hslash \omega =0.2$ MeV. The energy difference between contour lines is 200 keV. The minimum points are indicated by the red dots. Calculated deformation parameters (${\beta }_2, \gamma$) are (a) (0.12, $-1^{\circ }$) for ${}^{106}\mathrm{Te}$; (b) (0.13, $-5^{\circ }$) for ($+, +$1/2) and (c) (0.15, ${10}^{\circ }$) for ($-, -$1/2) of ${}^{107}\mathrm{Te}$; (d) (0.14, $-2^{\circ }$) for ${}^{108}\mathrm{Te}$; and (e) (0.14, $-5^{\circ }$) for ($+, +$1/2) and (f) (0.16, $9^{\circ }$) for ($-, -$1/2) of ${}^{109}\mathrm{Te}$.