90,91Zr photoproton spectra and the core-excitation model

Abstract

Photoproton energy spectra have been measured for the 90,91Zr(γ,P) 89,90Y reactions at an E γ endpoint energy of 30 MeV, and for the 90,91Zr,(e, e'p) 89,90Y reactions at a number of different electron beam energies around E e = 21 MeV. Isotopically enriched target foils of metallic 90Zr(97.65%) and 91Zr(89.2%) were used, and the proton spectra measured at 90°. Prominent proton groups are observed in the 91Zr spectra, particularly around E p ≈ 11 MeV, which closely resemble groups produced in the 90Zr photoreactions. Moreover, the correlating non-ground state proton groups are being produced in transitions leaving the corresponding 89Y, 90Y residual nuclei in excited levels which also correlate in energy. These photoproton groups from 90Zr have previously been identified as representing T > strength. A qualitative explanation is proposed in terms of the core-excitation model, in which the structure in the 91Zr proton spectrum is described as representing dipole T > (T = 13 2 ) strength formed by coupling the 2d 5 2 neutron to dipole T > ( T = 6) excitations of a 90Zr core.