Fast first-forbidden transitions and subshell closures in the region of 96Zr

The low-spin β-decay of /sup 96,98/Y has been reinvestigated to obtain detailed informatin on the fast first-forbidden transitions to the ground states of /sup 96,98/Zr. A considerably more detailed decay scheme of 96Y confirms the general features of a previous study. The spin of the ground state of 98Y has been measured to be 0/sup /minus// from γγ(Θ) angular correlations in 98Sr → 98Zr decay and from Q/sub β/ measurements by β--γ coincidences in the decay of 98Y → 98Zr. From β-decay data on 90-100Y nuclei, mixing of the ''spherical'' and ''collective'' 0/plus/ states is deduced, and the strength of the mixing matrix elements is found to vary greatly across the Zr nuclei. 20 refs., 1 fig., 1 tab