Abstract
In-flight fission of a 345MeV per nucleon 238U primary beam on a 2mm thick 9Be target has been used to produce and study the decays of a range of neutron-rich nuclei centred around the doubly mid-shell nucleus 170Dy at the RIBF Facility, RIKEN, Japan. The produced secondary fragments of interest were identified event-by-event using the BigRIPS separator. The fragments were implanted into the WAS3ABI position sensitive silicon active stopper which allowed pixelated correlations between implants and their subsequent β-decay. Discrete γ-ray transitions emitted following decays from either metastable states or excited states populated following beta decay were identified using the 84 coaxial high-purity germanium (HPGe) detectors of the EURICA spectrometer, which was complemented by 18 additional cerium-doped lanthanum bromide (LaBr3) fast-timing scintillation detectors from the FATIMA collaboration. This paper presents the internal decay of a metastable isomeric excited state in the odd-odd nucleus 168Tb, which corresponds to a single proton-neutron hole configuration in the valence maximum nucleus 170Dy. These data represent the first information on excited states in this nucleus, which is the most neutron-rich odd-odd isotope of terbium (Z=65) studied to date. Nilsson configurations associated with an axially symmetric, prolate-deformed nucleus are proposed for the 168Tb ground state the observed isomeric state by comparison with Blocked BCS-Nilsson calculations.
Highlights
The single-particle structure of states in quadrupole-deformed nuclei in the vicinity of the 170 Dy valence maximum nucleus can be used as a measure of the magnitude of the deformation in these systems [1, 2]
We report on the decay of isomeric states in the neutron-rich systems 165 Tb and 167 Tb, and compare the deduced level schemes with long-standing predictions of which quasi-proton orbitals are favoured in this well-deformed region of the nuclear chart
The coincidence data and energy sum considerations imply that the 147 keV decay transition provides a parallel decay path from the isomeric state in 167 Tb which competes with a cascade of two, mutually coincident transitions of energy 73 keV
Summary
Wuc,n , H.L. Liuo , F.R. Xun , Z. Kanayam , J.J. Valiente-Dobónα a Department of Physics, University of Surrey, Guildford, b National Physical Laboratory, Teddington, UK
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