Yrast and nonyrast states in ${}^{126}\mathrm{Te}$

The yrast and nonyrast states of ${}^{126}\mathrm{Te}$ were populated in a fusion-evaporation reaction using a target of ${}^{124}\mathrm{Sn}$ and $\alpha$ beam at 31 MeV energy. All the $\gamma \text{−}\gamma$ coincidences were recorded using the Indian National Gamma Array at the Variable Energy Cyclotron Centre, India, and processed by a digital data-acquisition system. The level scheme was enriched with the addition of 65 new transitions and the identification of five new structures. Spin and parity assignments were made and the subsequent results were interpreted in the framework of the nuclear shell model using the large-scale shell-model code antoine.

Figure 1

The $R_{\mathrm{DCO}}$ values of the transitions as a function of $\gamma$-ray energy are plotted. The $R_{\mathrm{DCO}}$ values have been obtained in quadrupole gates. DCO value for a known stretched $E2$ transition gives a value of 1.05(1) while a pure dipole transition gives a value of 0.70(1).

Figure 2

The $\mathrm{\Delta }\mathrm{IPDCO}$ values of the transitions as a function of energy are plotted. Positive values indicate a predominantly electric-type nature whereas a negative value indicates a magnetic-type nature.

Figure 3

The positive-parity section of the level scheme of ${}^{126}\mathrm{Te}$ as obtained in the present work. The new $\gamma$ rays and levels are marked in red.

Figure 4

The negative-parity section of the level scheme for ${}^{126}\mathrm{Te}$ as obtained in the present work. The new $\gamma$ rays and levels are marked in red.

Figure 5

Spectra obtained from the $\gamma \text{−}\gamma \text{−}\gamma$ cube showing some of the transitions decaying to the yrast band. These transitions are placed in the positive-parity part of the level scheme. New transitions are marked in red. Panel (a) is a double gate on the 666- and 695-keV $\gamma$ rays. The transition marked ‘*’ is from ${}^{125}\mathrm{Te}$, which was also populated in this experiment. Panel (b) is the double gate 666/415 keV, and panel (c) is the double gate 1124/415. Insets have been employed to indicate the new (weaker) transitions more clearly. ($\gamma$-ray energies have been rounded off to the nearest integer.)

Figure 6

Spectra obtained from the $\gamma \text{−}\gamma$ symmetric matrix showing some of the transitions decaying to the yrast band. These transitions are placed in the positive-parity part of the level scheme. Transitions marked with ‘*’ are from ${}^{125}\mathrm{Te}$, which was also populated in this experiment. New transitions are marked in red. Panel (a) shows a single-gated spectrum on the 414.7-keV transition. Panel (b) is a single-gate on the 1125.4-keV $\gamma$ ray. ($\gamma$-ray energies have been rounded off to the nearest integer.)

Figure 7

Spectra obtained from the $\gamma \text{−}\gamma \text{−}\gamma$ cube with double gates showing some of the prominent transitions observed in coincidence. These transitions are placed in the positive-parity part of the level scheme. New transitions are marked in red. Transitions marked with “*” are from ${}^{125}\mathrm{Te}$, which was also populated in this experiment. Panel (a) is a double gate on the 863- and 209-keV $\gamma$ rays, panel (b) is the double gate 415-695 keV, and panel (c) is the double gate 713-209. Panel (b) has been zoomed in to show the high-energy transitions prominently. ($\gamma$-ray energies have been rounded off to the nearest integer.)

Figure 8

Spectra obtained from the $\gamma \text{−}\gamma \text{−}\gamma$ cube with double gates showing some of the prominent transitions observed in coincidence. These transitions are placed in the positive-parity part of the level scheme. Transitions marked with “*” are from ${}^{125}\mathrm{Te}$, which was also populated in this experiment. The top panel is the spectrum obtained with a single gate on the 1064-keV transition. The newly observed transitions are marked in red. Both the 730- and 134-keV transitions decay to the 2839.7-keV level of structure P1. The middle panel is the double gate 356-1064. The bottom panel shows a gate on the 1064- and 134-keV transitions. The presence of all the $\gamma$ rays in this cascade and the absence of the 134-keV transition in the 1064-356 gate justifies the placement of this transition in the level scheme. ($\gamma$-ray energies have been rounded off to the nearest integer.)

Figure 9

Spectra obtained with double gates showing some of the prominent transitions observed in coincidence. These transitions are placed in the negative-parity part of the level scheme. New transitions are marked in red. Panel (a) is a double gate on the 856- and 695-keV $\gamma$ rays, panel (b) is the double gate 572-695, and panel (c) is the double gate 572-412. ($\gamma$-ray energies have been rounded off to the nearest integer.)

Figure 10

Experimental energy levels and shell-model calculations for some of the levels of ${}^{126}\mathrm{Te}$. Newly observed experimental levels obtained in the present work are indicated in violet. The energy values have been rounded off to the nearest integer for brevity.

Figure 11

Experimental excitation energy relative to a rigid-rotor plotted against spin for the negative (top panel) and positive (bottom panel) structures. The total energy of a rigid rotor was calculated as $\approx 32.32A^{-5/3}\mathrm{I}$ ($\text{I}+1$) [36].

Figure 12

The potential-energy surfaces for some of the positive and negative-parity parity states obtained using the ultimate Cranker code. The $\gamma$ values for the negative-parity states (bottom panel) vary from $-41.4^{\circ }$ for $6^{-}$ to $-39.7^{\circ }$ for ${14}^{-}$ while for the positive-parity states (top panel), the values range from $-52.1^{\circ }$ for $9^{+}$ to $-32.7^{\circ }$ for ${15}^{+}$.

Figure 13

Experimental excitation energy relative to a rigid rotor plotted against spin for negative-parity bands (based on the $7^{-}$ level in ${}^{122,124,126}\mathrm{Te}$.

Figure 14

A comparison of the experimental level energies with the shell-model results for the new truncations.

Figure 15

A comparison of the experimental and shell-model excitation energies obtained in the present work.