Prolate-Oblate Shape Coexistence and Enhanced γ Softness in Neutron-Rich Nb and Mo Isotopes with A ≈ 110

The neutron-rich nuclei Nb-109 and Mo-110 have been investigated by means of beta-gamma and isomer spectroscopy following in-flight fission of a U-238 beam at 345 MeV/nucleon at the RIBF facility. A T-1/2 = 150(30) ns isomer at 313 keV has been identified in Nb-109. The low-lying levels in Nb-109 have been also populated following the beta-decay of Zr-109. The observed hindrances of the electromagnetic transitions deexciting the isomeric state are discussed in terms of possible shape coexistence. For Mo-110, spectroscopic information on the low-lying levels of the quasi-gamma band built on the 2(2)(+) state at 494 keV has been obtained for the first time. The experimental finding of the 2(2)(+) state being lower than the 4(1)(+) level suggests that axially-asymmetric gamma softness is substantially enhanced in this nucleus. The experimental results are compared with model calculations based on the general Bohr Hamiltonian method.