The interacting boson model is extended by the inclusion of selective noncollective fermion states through the successive breaking of the correlated S and D pairs (s and d bosons). High angular momentum states are generated in this way, and their structure described by the coupling between fermions in broken pairs and the boson core. The model space of bosons and broken pairs contains also unphysical states that are generated automatically when fermions couple to angular momenta ${\mathit{J}}_{\mathit{F}}$=0 and 2. A procedure is derived for the projection of spurious components from bases that contain one fermion pair. Spurious states are identified and an algorithm for their projection is constructed. The model is applied to the description of states in the spherical nucleus ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, and the weakly deformed nucleus ${}_{}{}^{82}{}_{}{}^{}\mathrm{Sr}$. Calculated spectra and transition probabilities are compared with experimental data. It is found that projection of spurious states from the model space is essential for a description of excited states with low angular momenta above the yrast, while it is less important for high-spin states close to the yrast line. © 1996 The American Physical Society.

• Received 23 June 1995

DOI:https://doi.org/10.1103/PhysRevC.53.1618