Yrast Octupole Excitations in the 146Gd Region

Octupole excitations frequently occur in the yrast lines of nuclei above 146Gd. One-particle phonon exchange coupling identified in the Tb isotopes gives rise to low-lying ΔI = 2 octupole excitations; two-particle phonon exchange coupling in Dy isotopes causes ΔI = 1 octupole excitations in the yrast lines above 3 MeV which deexcite by E1 transitions of 1 MeV. The predominant octupole nature of the low-lying 13/2+ states in the N = 83 nuclei is emphasized, and the two-phonon octupole character of a 19/2- level in 147Gd which decays by E3 to the 13/2+ (νf7/2 × 3-) state is discussed.