The ν9/2[404] orbital and the deformation in the A ∼ 100 region

A T1/2 = 16(2)ns isomeric level, populated in the spontaneous fission of 248Cm, has been found in 101Zr at 941.8keV in a measurement of prompt γ-rays using the EUROGAM2 array. The level is interpreted as a K-isomer corresponding to the 9/2[404] neutron-hole excitation. The quadrupole moment, Q0 = 3.6(4)eb, deduced for the new band indicates a large deformation of β2 = 0.38(4), which is produced by a specific shape-coexistence mechanism. This is another observation of the ν9/2[404] orbital in the mass A ∼ 100 region, confirming the presence of the effect reported first in our previous work. The 9/2[404] neutron-hole excitation is also confirmed in the 97Sr nucleus and the deformation β2 = 0.44(2) is determined for this configuration. The properties of the 9/2[404] neutron orbital and its influence on the onset of deformation in the A ∼ 100 region are discussed.