Search for nuclei exhibiting the U(5) dynamical symmetry

The level energy spectra of a set of 26 nuclei presenting a vibrational structure were analysed using a simple U(5) prescription in the IBM-1 framework. Twelve of these nuclei are relatively well fitted and present level patterns in accordance to the model predictions. They are thus confirmed or possible U(5) nuclei. The analysis suggests that they present extensive multiphonon structures. This implies the survival of such structures at higher energies. The experimental B(E2) values between multiphonon states are shown to agree with the finite N dependence predicted by the IBM. It is also observed that the 2+1 energies are quite generally about 15% lower than expected from the global nuclear properties. (orig.)