Development of axial asymmetry in the neutron-rich isotope 110Mo

Abstract

The neutron-rich nucleus 110Mo has been investigated by means of γ-ray spectroscopy following the β-decay of 110Nb, produced using in-flight fission of a 238U beam at 345 MeV/nucleon at the RIBF facility. In addition to the ground-band members reported previously, spectroscopic information on the low-lying levels of the quasi-γ band built on the second 2+ state at 494 keV has been obtained for the first time. The experimental finding of the second 2+ state being lower than the yrast 4+ 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. The systematics of the low-lying levels in even-even A ≈ 110 nuclei is discussed in comparison with that in the neutron-rich A ≈ 190 region, by introducing the quantity Es/E(2+1), Es = E(2+2) − E(4+1) as a global signature of the structural evolution involving axial asymmetry.