Direct and multiple excitations in 96Zr from inelastic-scattering experiments

The excitation of double closed subshell 96Zr is studied in polarized (d vector, d') as well as in unpolarized (p, p') and (d, d') reaction experiments at bombarding energies near 20 and 60 MeV. All excited states known from previous γ-spectroscopic studies have been resolved up to 4.1 MeV excitation energy. The data confirm that the low-lying spectrum is dominated by two-quasiparticle excitations, with the excitation strength being concentrated on the lowest states for each spin. The high collectivity of the 31- state is most remarkable and in line with recent level-lifetime results. The excitation energies and extracted isoscalar strengths compare well with QRPA results. Coupled-channel calculations, used to distinguish between one-step (two-quasiparticle) and two-step (four-quasiparticle) excitations, give only partial evidence concerning the existence of two-phonon octupole and quadrupole-octupole vibrational states. (orig.)