Recent measurements of $B\left(E2\right)$ values in even-even Te isotopes have revealed a smooth evolution of quadrupole collectivity, with only a slight asymmetry across the middle of the shell. These findings confirm that the only nucleus exhibiting an “anomalous” $B_{4/2}$ ratio ($B_{4/2}⩽1$) in even-even Te isotopes is ${}^{114}\mathrm{Te}$. To further investigate this anomaly, lifetime measurements were carried out in the odd-mass isotope ${}^{115}\mathrm{Te}$ ($N=63$), focusing on the $15/2^{-}$ and $19/2^{-}$ negative-parity levels in the $\nu h_{11/2}$ band, which are the analog states of the $2^{+}$ and $4^{+}$ levels in neighboring even-even nuclei. The extracted $B\left(E2\right)$ values for ${}^{115}\mathrm{Te}$ indicate a “normal” behavior, with a $B_{4/2}$ ratio greater than unity, further restricting the extent of the anomalous region in Te isotopes with $B_{4/2}⩽1$ to the lower mass region with $A⩽114$. The results have been interpreted using multiple theoretical frameworks: the shell model with the realistic pairing plus multipole terms with monopole interaction, large-scale configuration-interaction shell-model calculations, and the interacting boson-fermion model with triaxial deformation. The models give a fair reproduction of the experimental data, but fail to capture the detailed trend in the case of the $B_{4/2}$ values.

Close

PrevNext

View figure in article

• Collective levels
• Electromagnetic transitions
• Lifetimes & widths
• Nuclear structure & decays
• 90 ≤ A ≤ 149
• Collective models
• Shell model