Lifetime measurements of the first $2^{+}$ states in ${}^{116,118}\mathrm{Te}$

The lifetimes of the first $2^{+}$ states in ${}^{116,118}\mathrm{Te}$ were measured by means of the recoil distance Doppler-shift technique with the CIAE-plunger coupled to a HPGe array via ${}^{107}\mathrm{Ag}({}^{12}\mathrm{C},3n)$ and ${}^{110}\mathrm{Pd}({}^{12}\mathrm{C},p3n)$ reactions, respectively. The spectra are analyzed using the differential decay curve method. An improved precision for the lifetime of the $2_1^{+}$ state in ${}^{118}\mathrm{Te}$ was obtained, $\tau \left(2_1^{+}\right)=8.2\left(5\right)$ ps, as well as a first measurement of the $2_1^{+}$ state in ${}^{116}\mathrm{Te}, \tau \left(2_1^{+}\right)=5.1\left(3\right)$ ps. The lifetime values complete the systematic data near midshell and contribute to the understanding of how quadrupole collectivity evolves in this mass region. The resulting $B(E2,0_1^{+}\to 2_1^{+})$ transitions strength are discussed in relation to the systematics of the previously reported $B(E2,0_1^{+}\to 2_1^{+})$ values in the Te isotopes and compared to the predictions of several models.

Figure 1

Top panel: Systematics of $2^{+}$ and $4^{+}$ level energies for even mass Te isotopes; Bottom panel: Systematics of $B(E2,0_1^{+}\to 2_1^{+})$ values for even mass Te isotopes compared with empirical data (square) derived from experimental $2_1^{+}$ energies according to the formula proposed by Pritychenko, Birch, and Singh [22]. The experimental data marked with circles are taken from Refs. [20, 21]. The neutron midshell at $N=66$ is marked with the dashed vertical line.

Figure 2

Partial level schemes of ${}^{116,118}\mathrm{Te}$ for the data analysis in the present study according to Refs. [31, 32, 33].

Figure 3

Spectra of the $2^{+}\to 0^{+}$ transitions in ${}^{116,118}\mathrm{Te}$ at backward angle (${149}^{\circ }$) for three plunger distances. Left panel for ${}^{116}\mathrm{Te}$ obtained by gating on the tail of the shifted component of the 681 keV (2 keV wide from 686 keV to 688 keV), $4^{+}\to 2^{+}$ transition at forward angle ${31}^{\circ }$; right panel for ${}^{118}\mathrm{Te}$ obtained by gating on the shifted component of the 601 keV (3.5 keV wide from 593 keV to 596.5 keV), $4^{+}\to 2^{+}$ transition at backward angle ${149}^{\circ }$. The red and blue lines correspond to the shifted and unshifted components, respectively. The peak in the far-right of the right panel show the shifted component of the $6^{+}\to 4^{+}$ transition.

Figure 4

Portion of the spectrum showing multipeaks of the $2^{+}\to 0^{+}, 4^{+}\to 2^{+}$ transitions, and their shifted transitions at forward angle ${31}^{\circ }$. The histogram show the experimental data together with a fit function of four gaussian functions, as well as their decomposition.

Figure 5

DDCM analysis of $2_1^{+}$ state in ${}^{116}\mathrm{Te}$ (left) and the $2_1^{+}$ state in ${}^{118}\mathrm{Te}$ (right) gated by the direct feeders. In the upper panels the $\tau$ curves are displayed, including the resulting lifetimes and their statistical errors. The middle and bottom panels depict the intensities of the shifted and unshifted, respectively, components of the $\gamma$ transitions of interest. See text for details.

Figure 6

Spectrum showing the $2^{+}\to 0^{+}$ and $6^{+}\to 4^{+}$ transitions in ${}^{118}\mathrm{Te}$ at forward angle (${31}^{\circ }$) obtained by gating on the shifted component of the 601 keV, $4^{+}\to 2^{+}$ transition at backward angle (${149}^{\circ }$). Because the decay has to happen before the compound nucleus stopped, only the shifted component of the $6^{+}\to 4^{+}$ transition is visible in this spectrum.

Figure 7

(a) Systematic $B(E2,0_1^{+}\to 2_1^{+})$ transition rates for the $N=64$, 66, and 68 isotones. (b) Systematic $B(E2,0_1^{+}\to 2_1^{+})$ transition rates for the Cd ($Z=48$), Sn ($Z=50$), and Te ($Z=52$) isotopic chains. Open symbols are adopted and recently measured values from Refs. [20, 21], while the values from this work for ${}^{116,118}\mathrm{Te}$ is represented by the filled symbols.

Figure 8

Evolution of experimental $B(E2,2_1^{+}\to 0_1^{+})$ values of even-even Te isotopes. The experimental results are compared with the recent LSSM (blue solid line) [29], PSM (red dash line) [71], and extend shell model with the quasi-SU(3) symmetry (green dotted line) [18] calculations. The open symbols are from Refs. [20, 21] and closed symbols are from the current work.