SYMMETRY CHANGING TRANSITIONS IN GAMMA-SOFT NUCLEI STUDIED IN THE INTERACTING BOSON MODEL

Within the framework of the interacting boson model (IBM-2) we analyze F-vector gamma transitions in gamma-soft nuclei for which the O(6) dy namical symmetry of the IBM provides an analytical description. For ce rtain parameter combinations, the IBM-2 Hamiltonian is invariant with respect to the d-parity operation which changes the sign of each d bos on. This:symmetry of the Hamiltonian is responsible for the existence of the d-parity quantum number which leads to selection rules for elec tromagnetic transitions. The breaking of the d-parity symmetry can be studied in mixed E2/M1 transitions, and especially the E2/M1 mixing ra tio of the 1(1)(+)-->2(1)(+) gamma transition turns out to be a sensit ive measure of IBM-2 parameters for gamma-soft nuclei.