Fragmentation of two-phonon γ vibration strength in deformed nuclei

The intrinsic E2 matrix elements between ΔK = 2 bands for 186,188,190,192Os have been deduced from previously measured interband E2 transition matrix elements after correcting for the coupling between the rotational and intrinsic motion. The ratio of the intrinsic E2 matrix element between the K = 4 and 2 bands to that between the K = 2 and 0 bands, together with the ratio of their excitation energies, provide strong evidence for the existence of rather pure harmonic double-phonon γ-vibrational excitation. A similar result is obtained for 232Th, whereas significant fragmentation of the two-phonon strength is deduced for 156Gd and 160Dy.