Summary
Excitation functions for the reactions12C(p, γ0) and12C(p, γ2+3) 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 ∼32 MeV; the former appears in all reaction channels except (p, γ2+3), while the latter shows up in the capture cross-sections and in the yield of the 4.43 MeV γ-ray. 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 state in13N at an excitation energy of 20.4 MeV has been identified with the giant-dipole resonance, while the presence ofE 1 andE 2 strength is suggested around 32 MeV.
Riassunto
Le funzioni di eccitazione per le reazioni12C(p, γ0) e12C(p, γ2+3) a energie di protone da 16 a 40 MeV sono state misurate usando uno spettrometro a coppie costituito da scintillatori NaI (Tl). Nel corso dello stesso esperimento si sono determinate le funzioni di eccitazione dei raggi γ da 4.43, 12.7 e 15.1 MeV provenienti dalla diffusione anelastica del protone. Una risonanza ad energia di protone 20 MeV appare in quasi tutti i canali di reazione, mentre una larga struttura a circa 32 MeV si è osservata nella sezione d’urto di cattura e nella funzione di eccitazione dei raggi γ da 4.43 MeV. Tali risonanze sono state interpretate, nell’ambito della teoria di Feshbach, come strutture intermedie nel nucleo composto13N. In particolare si è identificato lo stato a 20.4 MeV con la risonanza gigante di dipolo elettrico, mentre attorno a 32 MeV sembrano coesistere statiE1 edE2.
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Ferroni, S., Ricco, G., Rottigni, G.A. et al. Giant resonances in13N as doorway-states in the p+12C reaction. Nuov Cim A 35, 15–32 (1976). https://doi.org/10.1007/BF02730057
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DOI: https://doi.org/10.1007/BF02730057