Yrast Band Spectroscopy of $^164$W and the Systematics of the First i$_13 / 2$ Neutron Backbend in the Neutron Deficient Rare-Earth Nuclei

Gamma-ray transitions have been identified for the first time in 164W. The yrast band has been established up to 28+(30+) and the alignment of the first pair of i13/2 neutrons is observed at a rotational frequency h(cross) omega =0.29 MeV. Above h(cross) omega approximately 0.30 MeV the first pair of h11/2 protons are observed to gradually align with a strong interaction strength. The systematics of the neutron alignment in nuclei ranging from Dy to W and with neutron numbers from 88 to 98 are discussed. The variations of alignment frequency with neutron and proton number are explained in terms of changes in quadrupole and hexadecapole deformation and the changing position of the Fermi surface in relation to the aligning neutron orbitals.

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