Multipole mixing ratios in the decay of 133Ba from triple-γ directional correlation measurements

The multipole mixing ratios of the 53.17 and 302.85 keV transitions in 133Cs are measured through γ -> γ -> γ angular correlation experiments using one NaI(Tl) and two Ge(Li) detectors. Angular correlations for the cascades 276.40 keV -> 79.63 keV (THETA variable) -> 81.00 keV, 276.40 keV -> 79.63 keV -> 81.00 keV (THETA variable), and 53.17 keV -> 302.85 keV -> 81.00 keV (THETA variable) were investigated. The data were analyzed assuming the presently accepted Jsup(π) sequence of 7/2+, 5/2+, 5/2+, 3/2+, and 1/2+ for the ground state and the 81.00, 160.63, 383.82, and 437.00 keV levels in 133Cs, respectively, and taking the 276.40 keV transition to be pure E2, the 81.00 keV transition to be M1 + 2.8% E2, and the 53.17 keV transition to be M1 + 1.0% E2. The multipole mixing ratios delta are determined to be +0.171 (+0.051-0.050) for the 79.63 keV transition and +0.022 for the 302.85 keV transition. Phases of the mixing ratios of the 81.00, 79.63, and 302.85 keV transitions are adopted after a critical analysis of the data. The present experiment has determined the mixing ratios, along with the phases, free of errors due to angle-dependent Compton distributions of interfering γ-ray cascades. (orig.)