Study of the soft dipole modes in ¹⁴⁰Ce via inelastic scattering of ¹⁷O

The main aim of this study was a deeper understanding of the nuclear structure properties of the soft dipole modes in ¹⁴⁰Ce, excited via inelastic scattering of weakly bound ¹⁷O projectiles. An important aim was to investigate the ‘splitting’ of the PDR into two parts: a low-energy isoscalar component dominated by neutron-skin oscillations and a higher-energy component lying on the tail of the giant dipole resonance of a rather isovector character. This was already observed for this nucleus, investigated in (α, α′) and (γ, γ′) experiments. The experiment was performed at Laboratori Nazionali di Legnaro, Italy. Inelastic scattering of ¹⁷O ion beam at 20 MeV A^–1 was used to excite the resonance modes in the ¹⁴⁰Ce target. Gamma-rays were registered by five triple clusters of AGATA-Demonstrator and nine large volume scintillators (LaBr₃). The scattered ¹⁷O ions were identified by two ΔE – E Si telescopes of the TRACE array mounted inside the scattering chamber. The telescopes consisted of two segmented Si-pad detectors, each of 60 pixels. Very preliminary data have shown a strong domination of the E1 transitions in the ‘pygmy’ region with a character more similar to the one obtained in alpha scattering experiment