Anomalous properties of quadrupole collective states inTe136and beyond

Abstract

The ground and low-lying states of neutron-rich exotic Te and Sn isotopes are studied in terms of the nuclear shell model by the same Hamiltonian used for the spherical-deformed shape phase transition of Ba isotopes, without any adjustment. An anomalously small value is obtained for $B(E2;{0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ in $^{136}\mathrm{Te}$, consistent with a recent experiment. The levels of $^{136}\mathrm{Te}$ up to yrast ${12}^{+}$ are shown to be in agreement with observed ones. It is pointed out that $^{136}\mathrm{Te}$ can be an exceptionally suitable case for studying mixed-symmetry ${1}^{+}$, ${2}^{+}$, and ${3}^{+}$ states, and predictions are made for energies and $M1$ and $E2$ properties. Systematic trends of structure of heavier and more exotic Sn and Te isotopes beyond $^{136}\mathrm{Te}$ are studied by the Monte Carlo shell model, presenting an unusual and very slow evolution of collectivity/deformation.