Journal
PHYSICS LETTERS B
Volume 823, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.physletb.2021.136738
Keywords
Nuclear isomers; gamma-ray spectroscopy; LaBr3 detectors; Transition rates; Nuclear collectivity; Nuclear shell model
Funding
- Australian Research Council [DP170101673, DP170101675]
- International Technology Center Pacific (ITC-PAC) [FA520919PA138]
- Australian Government Research Training Program
- Australian National Collaborative Research Infrastructure Strategy (NCRIS) program
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Excited-state lifetimes were measured in three N = 125 isotones, showing almost identical transition energies for the first excited state to ground state transition. The role of protons as spectators increases along the isotone chain, with large-basis shell-model calculations underestimating the experimental values. The near-constant transition energies are attributed to complex nucleon-nucleon correlations enhancing quadrupole collectivity beyond the shell-model valence space.
Excited-state lifetimes were measured by direct fast-timing methods in three N = 125 isotones - Po-209, Rn-211, and Ra-213 - near doubly magic Pb-208. These nuclei have a single neutron hole and successively add pairs of protons relative to Pb-208. The first-excited state to ground-state transition, 5/2(1)(-) -> 1/2(1)(-), has almost identical energy in each isotone and can be associated with the single neutron-hole transition nu f(5/2)(-1) -> nu p(1/2)(-1). The extent to which the protons act as spectators is assessed based on the measured transition rates, which show a systematic increase along the isotone chain, and by comparisons with large-basis shell-model calculations. The shell model accounts for some of the increased transition strength but consistently underestimates the experimental values. It also fails to explain the near-constant transition energies. These results suggest emerging collectivity beyond the shell-model valence space and show that the near-constant transition energies are not a consequence of a pure neutron-hole transition, but rather the outcome of complex nucleon-nucleon correlations that increase quadrupole collectivity. (C) 2021 The Author(s). Published by Elsevier B.V.
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