Abstract
Very neutron-rich isotopes produced by in-flight fission of a 345 MeV/nucleon beam at the RI Beam Factory, RIKEN Nishina Center, have been studied by delayed -ray spectroscopy. New isomers were discovered in the neutron-rich isotones , and . Half-lives, -ray energies, and relative intensities of these isomers were obtained. Level schemes were proposed for these nuclei and the first and states were assigned for the even-even nuclei. The first and state energies decrease as the proton numbers get smaller. The energies and the half-lives of the new isomers are very similar to those of isomers known in less neutron-rich isotones and . A deformed Hartree-Fock with angular momentum projection model suggests two-quasiparticle states with configurations with similar excitation energy. The results suggest that neutron-rich nuclei are well deformed and the deformation gets larger as decreases to 62. The onset of isomers with the same configuration at almost the same energy in isotones indicates that the neutron single-particle structures of neutron-rich isotones down to do not change significantly from those of the stable nuclei. Systematics of the excitation energies of new isomers can be explained without the predicted shell gap.
- Received 10 December 2016
- Revised 1 February 2017
DOI:https://doi.org/10.1103/PhysRevC.95.034313
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