Structure of low-lying states in128Bafromγ−γangular correlations and polarization measurements

Abstract

A study of the low-lying levels of ${}^{128}\mathrm{Ba}$ was performed using three clover detectors in a compact arrangement. The levels were populated by beta decay of ${}^{128}\mathrm{La}$ which was produced by the fusion evaporation reaction ${}^{116}{\mathrm{S}\mathrm{n}(}^{16}\mathrm{O},1p3n).$ $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ angular correlations and polarization measurements were performed. The decay properties of several low-lying states were investigated. Spin assignments were made for two states, and several $E2/M1$ mixing ratios were determined. The results are in good agreement with predictions of the O(6) limit of the interacting boson approximation. One of the states is unambiguously determined to be the hitherto unobserved member of the $\ensuremath{\tau}=4$ multiplet.