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The 12C(p,y)13N reaction Berghofer, David

Abstract

The ninety degree yield curve for the ¹²C(p,Ƴ) ¹³N reaction was examined for proton energies (Ep ) between 14 MeV and 24.4 MeV using a 99.9 % pure carbon-12 target and protons from the University of Washington FN tandem Van de Graaff. The giant dipole resonance (GDR) for the gamma transition to the ground state (Ƴ₀) was found to be centered at Ep = 20.5 MeV with a width Γ = 4 MeV and a maximum cross-section = 3 µb/sr. Intermediate structure of width Γ = 1 MeV was observed at Ep = 17.5 MeV and 23 MeV. The yield curve was compared to the ¹¹B(p,Y₀) ¹²C yield curve, and the similarities found indicated that valence nucleon transitions to the ground state play little part in the GDR of 13N. Yield curves for the transition to the first excited state (Ƴ¹) and the sum of the transitions to the second and third excited states (Ƴ2+3) are also given in the regions where they can be reliably extracted. No fine structure was observed. Measured yields of the 12.71 MeV and 15.11 MeV gamma-rays from the inelastic reaction agree well with other recent results. Proton decay widths to these states from compound nuclear states in 13N are given. Angular distributions for the (p, Ƴ₀) reaction were measured at six energies in the region of the "pygmy resonance" Ep= 10 MeV to 14 MeV, to inspect previously reported fine structure. Two narrow minima seen in the ninety degree yield are found to be minima in the integrated cross-sections, whereas the shape of the angular distribution is relatively constant.

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