Abstract
Here we present new information on the shape evolution of the very neutron-rich nuclei from an isomer-decay spectroscopy experiment at the Radioactive Isotope Beam Factory at RIKEN. High-resolution germanium detectors were used to identify delayed rays emitted following the decay of their isomers. New transitions are reported extending the previously known level schemes. The isomeric levels are interpreted as originating from high- quasineutron states with an oblate deformation of , with the high- state in being metastable and hindered. Following this, is the lowest-mass neutron-rich nucleus known to date with such a substantial hindrance. Furthermore, it is the first observation of an oblate isomer in a deformed nucleus. This opens up the possibility for a new region of isomers at low and at oblate deformation, involving the same neutron orbitals as the prolate orbitals within the classic deformed hafnium region. From an interpretation of the level scheme guided by theoretical calculations, an oblate deformation is also suggested for the ground-state band.
- Received 3 March 2020
- Revised 17 April 2020
- Accepted 12 May 2020
DOI:https://doi.org/10.1103/PhysRevLett.124.222501
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