The neutron-rich nuclei 109Nb and 109Zr have been populated using in-flight fission of a 238U beam at 345 MeV/nucleon at the \RIBF\ facility. A T 1 / 2 = 150 ( 30 ) ns isomer at 313 keV has been identified in 109Nb for the first time. The low-lying levels in 109Nb have been also populated following the β-decay of 109Zr. Based on the difference in feeding pattern between the isomeric and β decays, the decay scheme from the isomeric state in 109Nb was established. The observed hindrances of the electromagnetic transitions deexciting the isomeric state are discussed in terms of possible shape coexistence. Potential energy surface calculations for single-proton configurations predict the presence of low-lying oblate-deformed states in 109Nb.

The non-relativistic approximation of the quark–meson-coupling model has been discussed and compared with the Skyrme–Hartree–Fock model which includes spin exchanges. Calculations show that the spin-exchange interaction has important effect on the descriptions of finite nuclei and nuclear matter through the Fock exchange. Also in the quark–meson-coupling model, it is the Fock exchange that leads to a nonlinear density-dependent isovector channel and changes the density-dependent behavior of the symmetry energy.