The/~-decay of a~ has been investigated at the fission-product separators JOSEF and LOHENGRIN. The half-life of a~ has been determined to 2.5(1)s and a level scheme for t~ has been established from 7 ray singles as well as X-7 and 7-7 coincidence measurements. Conversion coefficients for transitions in l~ and level half-lives between 10 ps and 2 ns have been determined. Three rotational bands are identified among the low-lying levels with band heads at 0 keV, 206 keV and 208 keV. The bands are probably based on the Nilsson configurations [422 5/2+], [301 3/2-] and [303 5/2-], respectively. The deformation has been determined to /?q=0.40(4) and 0.41(8) for the ground state band and the band based on the 206 keV level from the half-lives of the first and second excited members of these bands. This shows that the rapid onset of deformation at N = 60 which is typical for the A = 100 region of neutron-rich nuclei, takes also place in the Nb isotopes. Nilsson model calculations describe the experimental data well, especially the several determined transition probabilities including those for E1 transitions from the 206 and 208 keV band heads to the ground state.

Life-times of low-lying levels in 9~Rb54 and 3vRb56 have been determined from/~ -7 coincidence measurements at the fission-product separator JOSEF. Values of t~/2 = 17.0(8)ns and 2.0(2)ns have been obtained for the levels at 1,134 keV in 91Rb and 267 keV in 93Rb, respectively, and upper limits could be deduced for several other states. Calculations in the frame of IBFM/PTQM have been performed for 91Rb, the results of which allow an interpretation of the low-lying levels of this nucleus. For the 1,134 keV level the configuration [7rg9/2@2 +] 7/2 + is suggested which lies close to or even below the 9/2[ level. The calculated half-life of 14 ns for the 1,134 keV level reproduces well the experimental value. The half-life of the 267 keV level in 93Rb favours the assignment of I x = 1/2-to this state over the alternative 3/2-. PACS" 23.20.Ck; 21.60.Fw; 27.60. +j

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