Deeply-bound hole states and isobaric analog states in 89Zr.(II)

The 90Zr(tau,α)89Zr reaction, at 39MeV incident energy, was used to populate hole states up to 13.5MeV excitation energy in 89Zr. A split-pole spectrometer was used for particle analysis and detection. In the excitation energy range between 0 and 3.5MeV, about twenty well resolved states were observed in 89Zr, many for the first time. These states contain almost all of the spectroscopic strengths of the 1gsub(9/2), 2psub(1/2), 2psub(3/2) and 1fsub(5/2) neutron subshells. The 30-35keV energy resolution of the present study revealed a fine structure in the bump previously observed around 4.5MeV and tentatively identified as the main part of the 1fsub(7/2) hole orbital. About 30 levels or groups of levels were excited between 3.5 and 7.0MeV excitation energy and angular distributions have been extracted for each individual group as well as for the gross structure itself. A DWBA analysis of the data was carried out and shows that the main part of the observed fine structure is populated by l=3 angular momentum transfer. The full sum rule strengths obtained for the states below 3.5MeV for the pick-up of the 1gsub(9/2), 2psub(1/2), 2psub(3/2) and 1fsub(5/2) nucleon lead to the identification of this highly fragmented bump with the 1fsub(7/2) shell