Multiphonon states in 56136Ba80

Low-lying multiphonon states in Ba136 have been populated with the inelastic neutron scattering reaction. Excitation functions were performed at neutron energies from 2.2 to 3.9 MeV, and γ-ray angular distributions were measured at 2.5, 3.0, and 3.5 MeV. Lifetimes have been determined using the Doppler-shift attenuation method, and electromagnetic transition rates have been deduced. The previously assigned 21,ms+ mixed-symmetry state at 2128.9 keV has been confirmed and is not greatly fragmented. For the first time in the N=80 isotones, a 32,ms+ two-phonon mixed-symmetry state is proposed. In addition, the 25+ and the 43+ levels at 2222.7 and 2356.4 keV, respectively, decay with large B(M1) values to the two-phonon 22+ and 41+ states, respectively, which suggests two-phonon mixed-symmetric character. Their excitation energies, however, are not consistent with this interpretation.