Deformation dependence of the isovector giant dipole resonance: The neodymium isotopic chain revisited

Proton inelastic scattering experiments at energy $E_p=200\text{MeV}$ and a spectrometer scattering angle of 0° were performed on ^{144,146,148,150}Nd and ¹⁵²Sm exciting the IsoVector Giant Dipole Resonance (IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, ¹⁵⁰Nd and ¹⁵²Sm, exhibit a pronounced asymmetry rather than a distinct double-hump structure expected as a signature of K-splitting. This behaviour may be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data.