Low-spin states of153Gd observed in the decay of153Tb
Level structure of the 89-neutron nucleus153Gd has been investigated by studying theEC-decay of isotope-separated153Tb sources with several semiconductor detectors. In addition to singles gamma and electron spectra,γ-γ ande−-γ coincidences were investigated by using Ge(Li) and Si(Li) spectrometers and a high-capacity two-parameter recording system. In all, 191γ-rays are assigned to the decay of the 2.4d153Tb. The proposed level scheme of153Gd containing most of the observed transitions shows a very high density of low-spin states (45 states below 1.5MeV). Spin and/or parity assignments based mainly on coincidence data and measured transition multipolarities are proposed for a majority of these states. Nilsson model classifications of some levels are discussed. On the basis of logf t values the spin and parity of the ground state of153Tb are suggested to be 3/2+ or 5/2+.