A study of the photon-decay modes of the giant dipole resonance in even-A neodymium isotopes

This experiment measured the elastic and inelastic photon scattering cross sections into the ground and first excited state across the isotopic chain 142,146,148,150Nd between the energies of 12 and 18 MeV, spanning the peak of the Isovector Giant Dipole Resonance. Inelastic scattering into the β-band head in 148,150Nd and the γ-band head in 150Nd was also resolved. The measured cross sections were compared to predictions of both the Dynamic Collective Model and the Interaction Boson Model. A 100% duty-factor, 24 MeV electron beam provided the tagged, bremsstrahlung photons. The scattered photons were detected in two large NaI(Tl) crystals, whose energy resolution was typically ∼ 3%. This allowed the inelastic scattering cross sections to be resolved into the first excited state of all the nuclei studied, except 150Nd, where the scattering was separated by measuring the unresolved cross section at two different scattering angles. The Dynamic Collective Model was applied in the spherical and statically deformed symmetry limits. The spherical version was in good agreement with the measured cross sections in 142,146Nd and the deformed version was in good agreement in 150Nd. Neither symmetry limit of the Dynamic Collective Model was completely successful in 148Nd. The Interacting Boson Model was used with parameters taken from the literature, and was found to be in relatively good agreement with all the nuclei studied, except 142Nd, which must be excluded from this model because of a neutron shell closure