Half-life of the 15/2(+) state of I-135: A test of E2 seniority relations

The half-life of the 15/ 2(1)(+) state of the 3-valence-proton nucleus I-135 has been measured to be 1.74(8) ns using the EXILL-FATIMA mixed array of Ge and LaBr3 detectors. The nuclei were produced following the cold neutron-induced fission of a U-235 target at the PF1B beam line of the Institut Laue-Langevin. The extracted B(E2; 15/2(+) -> 11/2(+)) value enabled a test of seniority relations for the first time between E2 transition rates. Large-scale shell-model calculations were performed for Te-134 and I-135, and reinterpreted in a single-orbit approach. The results show that the two-body component of the E2 operator can be large whereas energy shifts due to the three-body component of the effective interaction are small