Structure of Xe-126,Xe-128 studied in Coulomb excitation measurements

The electromagnetic properties of Xe-126,Xe-128 were studied in subbarrier Coulomb excitation measurements performed at the National Superconducting Cyclotron Laboratory Re-accelerator facility, ReA3, at Michigan State University (MSU). Xe-126 and Xe-128 nuclei were accelerated to 3.74 and 3.81 MeV/nucleon, respectively, and were impinged on Pt-196 and Pb-208 targets. The gamma rays deexciting the populated low-lying states were detected in coincidence with the scattered nuclei using the JANUS setup. Transition and diagonal matrix elements for low-lying states and transitions in Xe-126,Xe-128 were extracted from the experimental data using the GOSIA and GOSIA2 codes. The experimental results were compared with the theoretical calculations by the microscopic shell model and the Davydov-Filippov gamma-rigid rotor model. The calculated results from the newly established shell model (called the PMMU model), which is based on the advanced Hartree-Fock Bogoliubov plus generator coordinate method (HFB + gcm) for a large model space, agree well with the measurements in both nuclei, except for the second 2(+) state. Interpretation for the experimentally determined nearly vanishing electric-quadrupole moment of this state remains a challenge for theory.