Excited States and Collectivity in ⁸⁸Se

¹ Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble Alpes, CNRS/IN2P3, Grenoble INP, F-38026 Grenoble, France
² Institut Laue-Langevin, 71 avenue des Martyrs, 38042 Grenoble Cedex 9, France
³ Université de Strasbourg, IPHC, 23 rue du Loess 67037 Strasbourg, CNRS, UMR7178, 67037 Strasbourg, France
⁴ Grand Accélérateur National d’Ions Lourds, CEA/DRF-CNRS/IN2P3, Boulevard Henri Becquerel, F-14076 Caen, France
⁵ INFN, via Marzolo 8, 35131 Padova, Italy
⁶ ELI-NP/IFIN-HH, 30 Reactorului Str., 077125 Magurele, Romania
⁷ Faculty of Physics University of Warsaw, ulica Pasteura 5, PL-02-093 Warsaw, Poland

^* e-mail: simpson@lpsc.in2p3.fr

Published online: 14 November 2018

Abstract

The γ decays of excited states in the very neutron-rich nucleus ⁸⁸Se have been observed following the cold neutron-induced fission of ²³⁵U 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 ⁸⁸Se. 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 ⁷⁸Ni 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 ⁸⁸Se being a transitional nucleus, possessing weak static β deformation and γ instability.