Level structure of 99Nb

The beta decay of Sr-97 to Y-97 has been investigated using ion-guide on-line mass separation and a 10 Ge-detector array to record gamma-gamma coincidences to a detection limit well below that of former studies. Similarities are found in the P-decay patterns of Zr-99 and of its isotone Sr-97 and also in the gamma-ray decay rates and branchings of the corresponding levels in their respective daughters Nb-99 and Y-97. This indicates a persisting influence of the d(5/2) neutron shell closure for Nb-99. The level structure of Nb-99 and the P-feeding pattern are discussed in the frame of the interacting boson-fermion plus broken pair model and the microscopic quasiparticle phonon model.