Effect of deformation on the broad and fine structure of the Isovector Giant Dipole Resonance in 142-150 Nd and 152 Sm

Abstract

This study investigates the e ect of nuclear deformation on both the broad and ne structure of the Isovector Giant Dipole Resonance (IVGDR) in the rareearth region. The IVGDR is strongly excited at and close to zero degrees by virtual-photon Coulomb excitation. As such, the Zero-degree Facility of the K600 magnetic spectrometer of iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) was used with an incident proton beam energy of 200 MeV to measure high energy-resolution (p,p0) scattering on a range of neodymium isotopes from spherical 142 60Nd82 to the permanently deformed 150 60Nd90 and the correspondingly deformed 152 62Sm90 in the region of the IVGDR. It is important to note that for nuclei with 88 N 92, a detailed study of the IVGDR is of speci c interest since it is here that a transition from spherical to permanently deformed nuclei occurs. An extensive data analysis procedure was performed, which included cross section extraction and conversion to equivalent photo-absorption spectra for comparison with existing photo-absorption data and theoretical predictions. For the more deformed 150Nd and 152Sm nuclei, however, the data from this study lack the expected double-peaked structure resulting from the splitting of the IVGDR into K = 0 and K = 1 components, and display a signi cant reduction in the strength of the K = 0 component of the IVGDR in comparison to previously published photo-absorption spectra. This reduced strength near the neutron threshold agrees very well with recent photo-neutron experiments. A ne structure analysis was performed on all of the measured isotopes, that is, 142;144;146;148;150Nd and 152Sm through the use of techniques associated with ii the continuous wavelet transform. Characteristic energy scales for the present high energy-resolution data are extracted using the complex Morlet motherwavelet and compared to those obtained for the theoretically predicted B(E1) strength functions. Finally, conclusions regarding the suitability of the model predictions to the current data are drawn.