Anomalous Properties of Quadrupole Collective States in ${}^{136}$Te and 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 $B(E2;0_1^{+}\to 2_1^{+})$ in ${}^{136}$Te, consistently with a recent experiment. The levels of ${}^{136}$Te up to yrast $12^{+}$ are shown to be in agreement with observed ones. It is pointed out that ${}^{136}$Te can be an exceptionally suitable case for studying mixed-symmetry 1${}^{+}$, 2${}^{+}$ and 3${}^{+}$ states, and predictions are made for energies, M1 and E2 properties. Systematic trends of structure of heavier and more exotic Sn and Te isotopes beyond ${}^{136}$Te are studied by Monte Carlo Shell Model, presenting an unusual and very slow evolution of collectivity/deformation.

Comments: 8 pages, 7 figures, accepted for publication in Phys. Rev. C