Yrast superdeformed bands of A ≈ 190 nuclei are systematically described by the projected shell model. The calculated γ-ray energies are compared with experimental data for which spins are unambiguously assigned. The excellent agreement between the calculation results and available data provides a microscopic description of the different behaviours of the moment of inertia between even–even and odd–even nuclei in this mass region.

The positive, high-spin states of the 155-165Er isotopes are studied within the framework of the interacting boson-fermion model. The single fermion is assumed to be in the I = (13/2) orbit only. It was found that the calculated positive high-spin state energy spectra of the odd Er isotopes agree quite well with the experimental data. Also, the observed order reversal of the adjacent spin doublet states of the energy spectra for 159-163Er has been successfully reproduced. The B(E2) values for 157-163Er are calculated and compared with the experimental data.