Proton alignments at high rotational frequency in 167,168Yb

High-spin states in ¹⁶⁷Yb and ¹⁶⁸Yb have been investigated using the ¹²⁴Sn( ⁴⁸Ca, x n) reaction at a bombarding energy of 210 MeV. The level sequences of the two nuclei were established from a large set of high-fold γ-ray coincidence data detected in the EUROGAM spectrometer. The experimentally observed upbends at high rotational frequency are discussed in terms of the cranked shell model for protons both with and without pairing. An unpaired crossing involving interchange of proton orbitals is tentatively identified. No evidence was found for hyperdeformation.