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A detailed level scheme for 221 Th has been established in an experiment using the 18 O + 207 Pb reaction at 96 MeV. The evaporation residues from this fissile system were selected with the HERCULES detector array and residue-gated γ rays were measured with Gammasphere. Three band structures of interlinked, alternating-parity levels are observed, two of which are non-yrast. In addition, several high-lying excitations are found. The yrast band is seen up to spin-parity 37/2 − and 39/2 + , beyond which a high-spin feeding transition is observed. The non-yrast sequences are interpreted as parity-doublet structures, based on a configuration similar to that of the yrast band in 223 Th (K = 5/2). The key properties of even-odd nuclei in this mass region [B(E1)/B(E2) and B(M 1)/B(E2) ratios, spin alignments, parity splittings] are reviewed.

Three discrete transitions were observed between the yrast superdeformed (SD) band and states of normal deformation (ND) in the nucleus 84 Zr. This is the first observation of such linking transitions in the mass-80 SD region. The properties of the decay out of the SD well in 84 Zr are compared with those in other SD mass regions. Calculations suggest that there is extensive mixing of configurations in the SD and ND potential minima, leading to an abrupt and highly fragmented decay-out process. A study of least-action tunneling paths indicates that the potential barrier separating the SD and ND wells is very small.