STRENGTH DISTRIBUTIONS IN NEODYMIUM ISOTOPES - A TEST OF COLLECTIVE NUCLEAR-MODELS

Excite states n even N isotopes, up to excitation energies of 3-4 MeV, were investigate in proton- and deuteron-scattering experiments perfo rmed with high-energy resolution. More than 300 transitions were studi ed. For several new excited states spin and parity assignments have be en suggested. Reduced transition probabilities were extracted for natu ral-parity states from 0+ up to 6+. The experimental strength distribu tions have been compared with the predictions of the interacting boson model (IBM) and of the quasi-particle-phonon model (QPM). The octupol e transition probabilities are well described in both models as produc ed by the fragmentation of the f-boson or of E3 phonons. IBM-sdf calcu lations seem to account also for the transitions to the low-lying 1- s tates. Quadrupole and hexadecapole distributions are well described in the QPM. The leading configurations are due to 6-8 low-lying one-phon on states. The two- and three-phonon states play an important role esp ecially in Nd-146. The failure of IBM quadrupole and hexadecapole calc ulations clearly points out the need of introducing additional bosons lying at high excitation energies. QPM evaluations account also for ot her features of the experimental data, as the E5 and E6 strength distr ibutions and the isovector components. The limits of the two models ar e discussed.