{gamma}-ray multipolarimetry between low-spin states of {sup 136}Ce: Search for the 2{sub 1,ms}{sup +} one-phonon mixed-symmetry state

An experiment was performed on {sup 136}Ce to measure E2/M1 multipole mixing ratios using the method of {gamma}{gamma} angular correlations. The low-spin states of interest were populated by {beta} decay from the 2{sup +} ground state of {sup 136}Pr that has a half-life of 13.1 min. Emitted {gamma} rays were detected with the Stony Brook cube germanium detector array. Five E2/M1 multipole mixing ratios were measured for the first time and two spin and parity quantum numbers were assigned. Candidates for the 2{sub 1,ms}{sup +} state of {sup 136}Ce were identified from large M1 fractions in the E2/M1 multipole mixing ratios. The 2{sub 1,ms}{sup +} state is suggested to be fragmented between the closely lying 2{sub 3}{sup +} and 2{sub 4}{sup +} states. A two state mixing scenario is employed for deducing an F-spin mixing matrix element of 43(5) keV.