Abstract
Theβ-decays of99Y and99Zr have been investigated with the two recoil fission product separators JOSEF and LOHENGRIN. Half-lives of 1.51±0.08s and 2.1±0.1s respectively, have been determined. Aβ-decaying isomeric state has been observed in99Y. The level schemes of4099Zr59 and4199Nb58 have been established fromγ-ray spectroscopy. Absoluteγ-intensities have been obtained by means of two independent techniques. Halflives of 293±10 ns for the 251.9 keV state and 10.2±1.5 ns for the 614.0 or 667.2 keV level in99Zr have been measured through delayedβ,γ- andγ,γ-coincidence experiments. Values for the spins and parities of the low lying levels in99Zr are proposed in accordance with the systematics of lighter odd Zr isotopes. Spins and partities are assigned to some levels in99Nb fromγ,γ-angular correlation measurements. In this nucleus there is evidence for three-particle configurations of some excited states, where the odd proton is coupled to two neutrons which are in different orbits.
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