Proton radiative capture: giant dipole resonances built on excited states

Recent experimental studies have been made for the radiative-capture reactions 11Bo(p,γ)12C and 27Al(p,γ)28Si leading to excited final states of 12C or 28Si. 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. It is argued 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 resonant 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