Forking and unusual decay out of superdeformed bands in 83Zr

Two superdeformed (SD) bands extending over eight to eleven transitions have been identified in 83Zr. The quadrupole moment of the more intense band was determined by the Residual Doppler Shift Method and is consistent with a quadrupole deformation of β2 ≈ 0.5. The large quadrupole moment and population intensity of the yrast SD band (≈ 5%) in Zr isotopes relative to their isotones in Sr and Y nuclei suggest the presence of a large SD shell gap at proton number Z = 40. At the decay-out points, the Routhians of the SD bands reapproach that of the positive parity normally-deformed states which may be the reason why both of these bands feed mainly (≈ 85%) into the positive-parity yrast band.