Giant resonances in 13N as doorway-states in the p+12C reaction

Excitation functions for the reactions 12C(p, γsub(deg) and 12C(p, γ23) at proton energies in the range 16 to 40 MeV have been measured by means of a scintillation pair spectrometer. In the course of the same experiment, the yields of 4.43, 12.7 and 15.1 MeV γ-rays following inelastic proton scattering have been determined as a function of the incident-proton energy. Resonances are observed at proton energies of 20 and approximately equal to 32 MeV; the former appears in all reaction channels except (p, γ23), while the latter shows up in the capture cross-sections and in the yield of the 4.43 MeV γ-rays. The information collected in the present experiment, complemented by data on proton elastic and inelastic scatterings obtained by other authors, has been interpreted in the framework of the doorway-state picture. The intermediate syaye in 13N at an excitation energy of 20.4 MeV has been identified with the giant-dipole resonance, while the presence of E1 and E2 strength is suggested around 32 MeV