First observation of the v9/2[404] orbital in the A～100 mass region

摘要

A new band, populated by the spontaneous fission of ~(248)Cm and studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array, was observed in ~(99)Zr. The 1038.8 keV band head with a half-life T_(1/2) = 54(10) ns is interpreted as a K-isomer, corresponding to the 9/2[404] neutron-hole excitation. It is the first observation of this orbital in the mass A～100 region. The quadrupole moment, Q_0 = 3.9 (3) eb deduced for the new band indicates a large deformation of β_2 = 0.41, which is produced by a specific shape-coexistence mechanism, known in other regions and now found in the A～100 nuclei.