Low-lying level structure of the neutron-rich nucleus 109Nb: A possible oblate-shape isomer

The neutron-rich nuclei Nb-109 and Zr-109 have been populated using 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 for the first time. The low-lying levels in Nb-109 have been also populated following the beta-decay of Zr-109. Based on the difference in feeding pattern between the isomeric and beta decays, the decay scheme from the isomeric state in Nb-109 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 Nb-109. (C) 2010 Elsevier B.V. All rights reserved.