Particle-core multiplets in 89Y

The 89Y nucleus has been formed in its excited states via the 87Rb(α, 2n) reaction at incident energies 24-34 MeV. The γ-ray decay of the states has been studied by measuring γ-γ-t coincidences, angular distributions and relative excitation functions. The experimental results from the present investigation are in general agreement with the former studies, however some corrections in the level scheme have been introduced. Eight new levels with spins up to around 31/2ℎ have been observed. The uppermost levels have been arranged into a rotational-like sequence suggesting a nuclear shape change. Using our and previously known data we have tried to locate and calculate the members of the 1g9/2 x core multiplet. The present results are compared with the semi-empirical shell model and the particle-core weak coupling description. (orig.)