Recent results of decay spectroscopy at RIBF

¹ RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
² International Research Center for Nuclei and Particles in the Cosmos, Beihang University, Beijing 100191, China
³ School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China

^a e-mail: hiroshi@ribf.riken.jp

Published online: 19 December 2013

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 T_1/2 = 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.