Excited States and Collectivity in 88 Se

The γ decays of excited states in the very neutron-rich nucleus 88 Se have been observed following the cold neutron-induced fission of 235 U at the PF1B facility of the Institut Laue-Langevin (ILL), Grenoble. The EXILL array was used to measure γ - γ - γ coincidences, which were then analysed to build a level scheme of 88 Se. A low (2 + 1 ) energy hints at the onset of quadrupole deformation and the identification of possible members of a (2 + 2 ) band provide evidence for γ vibrations. Shell-model calculations using a 78 Ni core reproduce the experimental decay scheme well, implying that interactions between particles in the π f 5/2 p and vsd orbits are responsible for much of the collectivity present. The algebraic collective model has also been used to interpret the experimental data, showing that that the experimental spectrum is consistent with 88 Se being a transitional nucleus, possessing weak static β deformation and γ instability.