Levels of ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}$ populated following the ${\beta }^{\mathrm{-}}$ decay of the $0^{\mathrm{-}}$ ground state of ${}_{}{}^{96}{}_{}{}^{}\mathrm{Y}$ have been investigated by γ-ray and conversion electron singles, γ-ray multispectral scaling, γ-γ and γ-${\mathrm{e}}^{\mathrm{-}}$ coincidence, and γ-γ angular correlation measurements. These data have been used to establish the population of eight excited levels of ${}_{}{}^{96}{}_{}{}^{}\mathrm{Zr}$, to confirm the $0^{+}$ assignment of the 2695-keV level, and to determine a half-life of 5.4(1) s for ${}_{}{}^{96}{}_{}{}^{}\mathrm{Y}$. The deduced beta transition strengths establish the decay to the ground state, with logft of 5.6, as one of the fastest first-forbidden decays known and support the notion of double subshell closure at Z=40 and N=56. The observed strong hindrance of transitions to excited $0^{+}$ states is indicative of shape coexistence. The observed level pattern of the band built on the $0_2^{+}$ state exhibits similarities to nearby vibrational-like nuclei having four valence protons and four valence neutrons. A four-particle, four-hole interpretation of the $0_2^{+}$ state is supported by the data, and we determine a deformation parameter, ${\beta }_2$∼0.2, for this intruder bandhead.

• Received 20 May 1987

DOI:https://doi.org/10.1103/PhysRevC.37.254