The neutron-rich nucleus ${}_{40}{}^{101}{}_{}{}^{}\mathrm{Zr}_{61}^{}{}_{}{}^{}$ has been studied at the isotope separator ISOLDE via the β decay of ${}_{}{}^{101}{}_{}{}^{}\mathrm{Y}$. A detailed level scheme has been obtained from γ-ray singles, γ-γ-t and β-γ-t coincidence measurements. The level structure of ${}_{}{}^{101}{}_{}{}^{}\mathrm{Zr}$ is similar to that of its isotone ${}_{}{}^{103}{}_{}{}^{}\mathrm{Mo}$ showing that, in contrast to their Sr neighbors, the Zr isotopes do not reach maximum of deformation immediately at its onset. This result is rather well reproduced by particle-rotor coupling calculations. A level systematics for the deformed N=61 isotones of ${}_{38}{}^{}{}_{}{}^{}\mathrm{Sr}$, ${}_{40}{}^{}{}_{}{}^{}\mathrm{Zr}$, and ${}_{42}{}^{}{}_{}{}^{}\mathrm{Mo}$ allows the assignment of Nilsson configurations to several rotational bands.

• Received 11 October 1994

DOI:https://doi.org/10.1103/PhysRevC.51.1211