Structure of120Tefrom the118Sn(α,2nγ)reaction and120Idecay

Abstract

The level structure of ${}^{120}\mathrm{Te}$ has been examined utilizing gamma-ray spectroscopy following the $(\ensuremath{\alpha},2n\ensuremath{\gamma})$ reaction and ${}^{120}\mathrm{I}$ decay. Excitation functions, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, and angular distributions were measured. Spectroscopic information, e.g., spins, branching ratios, and multipole-mixing ratios, was obtained for many new levels below 4.5 MeV in excitation energy. The level scheme was examined from the viewpoint of an anharmonic vibrator model, the general collective model, the particle-core coupling model, and interacting-boson-model-based intruder models. Particular aspects of the level sequence can be reproduced by each of these models, but the agreement with transition rate data is modest. The $B(E2)$ transition rate ratios are most consistent with the simple U(5) pattern. The higher-spin intruder states are identified in ${}^{120}\mathrm{Te}$ by comparison to the known band structures and decay patterns of the $N=66$ and $N=68$ tin and cadmium nuclei. The intruder signature vanishes below spin-8, where there is strong mixing between states.