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An odd-even neutron-number dependence of the alignment frequency of the first pair of t 13 / 2 quasineutrons in rare-earth nuclei is established. This effect is explained by a reduction of the neutron pairing-correlation parameter A" for odd-Af systems as compared to seniority-zero configurations in even-iV nuclei.

High-spin states in '66Yb have been studied via the '"Sm("0, 4n)'66Yb reaction with 80MeV I6O ions from the NBI tandem accelerator. y y coincidence data were accumulated with an array of four Ge(Li) and four NaI(TI) detectors to favour high multiplicity events. Totally about 3 X lo8 events were accumulated in the coincidence experiment. Measurements of the angular distribution of the yradiation and the conversion coefficients were furthermore performed. Four weakly populated side bands are observed besides the yrast cascade which is followed up to its 24' member. The ground state band has thus been identified to its 18' state, while the crossing Stockholm band becomes the yrast band from its 16+ member. The S-band is established from its 12+ state. The observed level energies and transition rates are well reproduced in-calculations within the particle rotor model.