Multiphonon structure of gamma -unstable or O(6) nuclei.

The multiphonon structure is shown for the O(6) limit of the interacting boson model. The phonon states are created by the O(6) quadrupole operator with proper symmetrization. All the [sigma]=[ital N] states can be described in this scheme in terms of phonon quanta and two-phonon anharmonicity, while the ground state is [gamma] unstable. This structure is carried over into higher-lying [sigma][lt][ital N] states.