Search for the two-phonon octupole vibrational state in 208Pb

We have performed an experiment to search for the two-phonon octupole vibrational state in Pb-208. Thick targets of Pb-208, Bi-209, Ni-58,Ni-64, and Gd-160 were bombarded with 1305 MeV beams of Pb-208 supplied by the ATLAS accelerator facility at Argonne. Gamma rays were measured using the Argonne-Notre Dame BGO gamma ray facility, consisting of 12 Compton suppressed Ge detectors surrounding an array of 50 EGO scintillators. We have identified some 30 known gamma rays from Pb-208 in coincidence spectra gated on low-lying transitions in Pb-208. In addition, after unfolding these spectra for Compton response, we observe broad coincident structures in the energy region expected for the decay of 2-phonon states. Furthermore, we have confirmed the placement of a previously observed 2485 keV gamma ray in Pb-207 and find no evidence consistent with the placement of this line in Pb-208.