Observation of dipole transitions to a 2[sup +][direct product]3[sup [minus]][direct product]particle multiplet in [sup 143]Nd

A photon scattering experiment on [sup 143]Nd yielded detailed information about the energies, cross sections, and absolute strengths of dipole transitions between 1.4 and 4.1 MeV. Besides some well-known levels at energies around 2 MeV we observed a number of very strong dipole excitations between 2.8 and 3.8 MeV. This is the energy region where one expects the two-phonon-(2[sup +][direct product]3[sup [minus]])[direct product] particle multiplet which arises due to the coupling of the unpaired neutron with (2[sup +][direct product]3[sup [minus]]) coupled states in the even-even core nucleus [sup 142]Nd. The summed dipole strength between 2.8 and 3.6 MeV in [sup 143]Nd, according to the sum rule, is comparable to the [ital E]1 strength of the 1[sup [minus]] member of the multiplet in the core nucleus [sup 142]Nd. Model calculations in a harmonic approximation with a quadrupole-quadrupole interaction show very good agreement with the experiment and indicate the dominant two-phonon-particle structure (2[sup +][direct product]3[sup [minus]][direct product][ital f][sub 7/2]) of the excitations in [sup 143]Nd.