Boson expansion theory description of anharmonic gamma vibrations in deformed nuclei

The boson expansion technique, extensively used in the past to describe anharmonic effects in spherical nuclei, is used to derive a boson formalism in a deformed basis (Nilsson model). The new formalism is then used to describe anharmonic gamma vibrations in 168Er. The Hamiltonian adopted for practical calculations includes monopole and quadrupole pairing, and quadrupole particle-hole interactions. Some effects due to the coupling of the collective-noncollective modes and a three-body interaction are also taken into account in a perturbative fashion