Gamma-ray spectroscopy and isomeric state lifetime measurements in 165−168Tb and 183Re.

This thesis presents measurements of electromagnetic decay probabilities for transitions in 183Re and 165-168Tb. The $^{183}$Re was formed using the fusion evaporation reaction 180Hf(7Li,4n)183Re at a beam energy of 30 MeV at the IFIN-HH Institute, Bucharest Romania. Coincident gamma rays from near-yrast cascades were detected using the combined HPGe-LaBr3(Ce) detector array ROSPHERE. The time differences between cascade gamma rays were measured to determine the half-lives of the two lowest-lying spin-parity 9/2- states at excitation energies of 496 and 617 keV to be 5.65(5) and 2.08(3) ns, respectively. The deduced E1 transition rates from these two states are discussed in terms of the K-hindrance in this prolate-deformed nucleus. Isomer spectroscopy of the very neutron-rich terbium isotopes 165, 166, 167, 168Tb is also presented. In-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm thick 9Be target was used to produce a range of neutron-rich nuclei centred around the doubly mid-shell nucleus 170Dy at the RIBF Facility, RIKEN, Japan. Discrete transitions emitted following decays from either metastable or excited states populated following beta decay were identified using the EURICA spectrometer. Metastable-state decays have been identified in the odd-A systems 165Tb and 167Tb and interpreted as arising from hindered E1 decays from the 7/2-[523] single quasi-proton Nilsson configuration to rotational states built on the 3/2-[411] single quasi-proton ground state. Possible two quasi-particle Nilsson configurations for the initial and final states which are linked by this transition in 166Tb are made on the basis of comparison with Blocked BCS Nilsson calculations, with the predicted ground state configuration for this nucleus arising from ν the coupling of the ν1/2-[521] and π3/2+[411] Nilsson orbitals. The thesis also presents data a metastable isomeric excited state in the odd-odd nucleus 168Tb. Nilsson configurations are proposed for the 168Tb ground state and the observed isomeric state by comparison with Blocked BCS-Nilsson calculations. These data correspond to the first spectroscopic information in the heaviest, odd-Z terbium isotopes