Anharmonic double-phonon excitations in the interacting boson model - art.no. 064309

Double-gamma vibrations in deformed nuclei are analyzed in the context of t he interacting boson model. A simple extension of the original version of t he model towards higher-order interactions is required to explain the obser ved anharmonicities of nuclear vibrations. The influence of three- and four -body interactions on the moments of inertia of ground and gamma bands, and on the relative position of single-gamma and double-gamma bands is studied in detail. As an example of a realistic calculation, spectra and transitio ns of the highly gamma -anharmonic nuclei Dy-164, Er-166, and Er-168 are in terpreted in this approach.