Shape and angular distribution of the 4.439-MeV $\gamma$-ray line from proton inelastic scattering off $^{12}$C

International audienceThe emission of the 4.439-MeV γ ray in proton inelastic scattering off C12 has been investigated in detail. For this, two independent descriptions of the correlated scattering and emission process have been used: one for the direct reaction mechanism and the other for the compound-nucleus (CN) component. Direct reactions were calculated in the framework of the coupled-channels formalism, while the CN component was described as a superposition of separate resonances with definite spin and parity, treated with the angular momentum coupling theory. Both components were incoherently added and compared to a comprehensive data set on measured γ-ray line shapes and angular distributions in the proton energy range Ep=5.44–25.0 MeV. In the range Ep≈14–25 MeV, good agreement with data was obtained with a dominating direct reaction component. At lower energy, an important CN component was required to describe line shape and angular distribution data. In general, a good description of the data could be found for a CN component with spin and parity corresponding to a known nearby resonance. The new calculation was found to improve significantly the agreement with line shape data in particular in the region of dominating CN resonances compared to previous calculations. Based on these results, predictions for γ-ray line shapes and angular distributions up to Ep=100 MeV were made and applied to γ-ray emissions in solar flares and proton radiotherapy