Multipole resonances in open-shell nuclei: Connection with direct-reaction spectroscopy

Probability distributions for the excitation of the 1ħω multipole resonances E1, M6, and M2 in the sd-shell nuclei ¹⁸O, ²²Ne, ²⁴Mg, ²⁶Mg, ²⁷Al, ²⁸Si, ³²S, and ⁴⁰Ca were obtained by means of the spectroscopy of direct pickup reactions within the particle-core coupling (PCC) version of the multiparticle shell model. The deviation of the ground state of a nucleus featuring A nucleons from the case of closed shells or subshells manifests itself in a broad range of the energy distribution of holes among states of (A − 1) nuclei. This energy spread is the main source of the fragmentation of multipole resonances in open-shell nuclei. A comparison of PCC theoretical results with experimental data confirms the applicability of the approach used over a broad range of momentum transfers and proves the existence of connections between direct and resonance processes.