A recently developed technique for fast timing measurements using β-γ-γ coincidences with plastic, ${\mathrm{BaF}}_2$ and Ge detectors, respectively, has been used to measure lifetimes in the range 5–1500 ps in the neutron-rich nuclei ${}_{}{}^{97}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{97}{}_{}{}^{}\mathrm{Y}$, and ${}_{}{}^{97}{}_{}{}^{}\mathrm{Zr}$. The results for ${}_{}{}^{97}{}_{}{}^{}\mathrm{Y}$ are interpreted in terms of quadrupole vibrational excitations. For ${}_{}{}^{97}{}_{}{}^{}\mathrm{Sr}$ the experimental data suggest the coexistence of spherical/vibrational and deformed states and allow the extraction of mixing matrix elements between them. A quadrupole moment of ‖${\mathit{Q}}_0$‖=3.5(4) e b for the deformed states in ${}_{}{}^{97}{}_{}{}^{}\mathrm{Sr}$ has been deduced.

• Received 22 September 1989

DOI:https://doi.org/10.1103/PhysRevC.41.1115