ISOMER SPECTROSCOPY OF NEUTRON-RICH (165,) Tb-167

Abstract

We present information on the excited states in the prolate-deformed, neutron-rich nuclei Tb-165, 167(100, 102). The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon U-238 primary beam on a 2 mm 9 Be target at the Radioactive Ion-Beam Factory (RIBF), RIKEN, Japan. The exotic nuclei were separated and identified event-by-event using the BigRIPS separator, with discrete energy gamma-ray decays from isomeric states with half-lives in the mu s regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in Tb-165 and Tb-167 and interpreted as arising from hindered E1 decay from the 7/2(-) [523] single quasi-proton Nilsson configuration to rotational states built on the 3/2(-) [411] single quasi-proton ground state. These data correspond to the first spectroscopic information in the heaviest, odd-A terbium isotopes reported to date and provide information on proton Nilsson configurations which reside close to the Fermi surface as the Dy-170 doubly-midshell nucleus is approached.