Collective and two-quasiparticle excitations in128Te

Abstract

Excited levels of ${}^{128}$Te to 3.3 in MeV excitation have been studied using $\ensuremath{\gamma}$-ray spectroscopy following inelastic scattering of accelerator-produced neutrons. Spectroscopic information, including transition energies, level spins, $E$2/$M$1 multipole-mixing ratios, and $\ensuremath{\gamma}$-ray branching ratios, was determined from $\ensuremath{\gamma}$-ray excitation functions measured from ${E}_{n}=2.15$--3.33 MeV in 90-keV increments, $\ensuremath{\gamma}$-ray angular distributions measured at ${E}_{n}=2.2$, 2.8, and 3.3 MeV, and $\ensuremath{\gamma}$$\ensuremath{\gamma}$ coincidences measured at ${E}_{n}=3.6$ MeV. Lifetimes of levels in ${}^{128}$Te 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.