Recent results of decay spectroscopy at RIBF

Abstract

The neutron-rich nuclei 109Nb and 110Mo have been investigated by means of β-γ and isomer spectroscopy following in-flight fission of a 238U beam at 345 MeV/nucleon at the RIBF facility. A T1/2 = 150(30) ns isomer at 313 keV has been identified in 109Nb. The low-lying levels in 109Nb have been also populated following the β-decay of 109Zr. The observed hindrances of the electromagnetic transitions deexciting the isomeric state are discussed in terms of possible shape coexistence. For 110Mo, spectroscopic information on the low-lying levels of the quasi-γ band built on the 22+ state at 494 keV has been obtained for the first time. The experimental finding of the 22+ state being lower than the 41+ level suggests that axially-asymmetric γ softness is substantially enhanced in this nucleus. The experimental results are compared with model calculations based on the general Bohr Hamiltonian method. A new project of decay spectroscopy at RIBF, named EURICA, is also introduced.