The first observation of a deformed Kπ=1+ ground-state band in 100Nb and the high-spin level scheme of its 4n fission partner 148La

The high-spin level schemes of odd–odd 100Nb (Z=41, N=59) and 148La (Z=57, N=91) were identified from γ–γ–γ coincidence studies of prompt γ rays in the spontaneous fission of 252Cf with Gammasphere. Spin/parity assignments for the levels in these two nuclei were made based on the low-lying levels assigned in decay work, on the internal conversion coefficient (ICC) measurements and the level systematics of the neighboring isotopes. A Kπ=1+ deformed ground-state band was identified in 100Nb. The onset of ground-state deformation in Nb isotopes is found to take place at N=59, in contrast to N=60 for Sr (Z=38), Y (Z=39) and Zr (Z=40) isotopes. Unlike the observation in 99Nb, the N=56 subshell closure seems to be no longer dominant in 100Nb. The bands observed in 148La are interpreted as aligned coupling of [πh11/2υh9/2]lowJ to the deformed core rotor.