Evidence for Coexisting Shapes through Lifetime Measurements in Zr-98

The lifetimes of the first excited 2(+), 4(+), and 6(+) states in Zr-98 were measured with the recoil-distance Doppler shift method in an experiment performed at GANIL. Excited states in Zr-98 were populated using the fission reaction between a 6.2 MeV/u U-238 beam and a Be-9 target. The gamma rays were detected with the EXOGAM array in correlation with the fission fragments identified by mass and atomic number in the VAMOS++ spectrometer. Our result shows a very small B(E2; 2(1)(+) -> 0(1)(+)) value in Zr-98, thereby confirming the very sudden onset of collectivity at N = 60. The experimenta(l) results are compared to large-scale Monte Carlo shell model and beyond-mean-field calculations. The present results indicate the coexistence of two additional deformed shapes in this nucleus along with the spherical ground State.