OCTUPOLE EXCITATIONS IN VIBRATIONAL NUCLEI AND THE SDF INTERACTING BOSON MODEL

Proton and deuteron inelastic scattering experiments, performed with an energy resolution of 12-15 keV, have been used to study negative-parity states of vibrational and transitional nuclei with mass between 98 and 150. The analysis has been focussed on the isovector components, on the quadrupole-octupole two-phonon states and on the fragmentation of the octupole strength. This latter displays a regular dependence on the product of proton and neutron valence particle numbers and is satisfactorily reproduced by IBM-1+f-boson calculations. Other features of the experimental spectra, as the relative positions of the 3- states, exhibit a dependence on the ratio of valence particle numbers and indicate that a IBM-2 approach might be more appropriate.