Collective and two-quasiparticle excitations in 128Te

Excited levels of 128Te to 3.3 in MeV excitation have been studied using γ-ray spectroscopy following inelastic scattering of accelerator-produced neutrons. Spectroscopic information, including transition energies, level spins, E2/M1 multipole-mixing ratios, and γ-ray branching ratios, was determined from γ-ray excitation functions measured from En=2.15-3.33 MeV in 90-keV increments, γ-ray angular distributions measured at E n=2.2, 2.8, and 3.3 MeV, and γγ coincidences measured at En=3.6 MeV. Lifetimes of levels in 128Te were deduced using Doppler-shift attenuation techniques. Absolute transition probabilities were determined for many levels and compared to interacting boson model and particle-core coupling model calculations to identify few particle and collective structures; states exhibiting the decay characteristics expected for two-phonon, mixed-symmetry, and quadrupole-octupole coupled states are identified. © 2012 American Physical Society.