Evidence for coexisting shapes in ${}^{98}$Zr through lifetime measurements

Abstract

The lifetimes of first excited 2${}^{+}$, 4${}^{+}$ and 6${}^{+}$ states in ${}^{98}$Zr were measured with the Recoil-Distance Doppler Shift method in an experiment performed at GANIL. Excited states in ${}^{98}$Zr were populated using the fission reaction between a 6.2 MeV/u ${}^{238}$U beam and a ${}^9$Be target. The $\gamma$ rays were detected with the EXOGAM array in correlation with the fission fragments identified in mass and atomic number in the VAMOS++ spectrometer. Our result shows very small B(E2;2${}_1^{+}$ $\to$ 0${}_1^{+}$) value in ${}^{98}$Zr thereby confirming the very sudden onset of collectivity at $N=60$. The experimental results are compared to large-scale Monte Carlo Shell model and beyond mean field calculations. The present results indicate coexistence of two additional deformed shapes in this nucleus along with the spherical ground state.