INTERPLAY BETWEEN SINGLE-PARTICLE AND COLLECTIVE DEGREES OF FREEDOM IN THE EXCITATION OF THE LOW-LYING STATES IN ND-142

The low-lying excited states in Nd-142 were investigated by inelastic electron scattering. The momentum transfer range covered was 0.5-2.8 fm-1. Transition charge densities were extracted for natural-parity states from 0+ up to 9- and up to an excitation energy of 3.5 MeV. For several new excited states spin and parity assignments have been suggested. The experimental transition charge densities have been interpreted with the aid of the quasiparticle-phonon model (QPM). The QPM is well-suited to investigate the contribution of collective and single-particle degrees of freedom to excited states in spherical nuclei. On the basis of the QPM calculations it is shown that in Nd-142 both degrees of freedom play an important role, as well as the interplay between them. Both the strength distribution and the structure of the transition charge densities of the low-lying excited states are well described by the calculations. The origin of the structure in the nuclear interior usually predicted by microscopic calculations but not observed experimentally is explained. An argument for the proton number dependence of the excitation energy of the 3(1)- state in the N = 82 isotones is given.