Rotational structure of highly deformedY99: Decay ofSr99

The level structure of the N=60 isotone ${}_{}{}^{99}{}_{}{}^{}\mathrm{Y}$ has been studied via the decay of ${}_{}{}^{99}{}_{}{}^{}\mathrm{Sr}$. γ singles and γ-γ coincidence measurements have resulted in 71 γ transitions placed in a decay scheme with 26 levels. γ-ray multiscaling measurements give a ${}_{}{}^{99}{}_{}{}^{}\mathrm{Sr}$ half-life of 270±10 ms. Five rotational bands, including the previously identified K=(5/2) ground-state band, have been identified in ${}_{}{}^{99}{}_{}{}^{}\mathrm{Y}$. Nilsson orbitals, with bandhead energies in keV in parentheses, associated with these five bands are (5/2)[422] (0), (5/2)[303] (487), (3/2)[301] (536), (1/2) [431] (1011), and (3/2)[431] (1119). The rotational features are consistent with an axially symmetric deformation in the range 0.3 to 0.4. The characteristics of these bands and their associated γ-ray transitions are discussed.