Proton radiative capture: Giant dipole resonances built on excited states

Abstract

Recent experimental studies have been made for the radiative-capture reactions11B(p, γ)12C and27Al(p, γ)28Si leading to excited final states of12C or28Si. All states of the final nucleus, which have a large component as a single proton times the ground state of the target nucleus, produce large radiative-capture cross-sections. These (p, γ) cross-sections show clear evidence of resonances. We argue that a qualitative description of these resonances can be made in terms of Brown’s “direct-semi-direct” theory of the giant dipole resonance (GDR). This theory describes the GDR in terms of a resonance energy, a width and a single-particle energy shift. The existing data indicate that both the resonant energy and shift, for the GDR built on excited states, are very close to the same values for the ground-state GDR.