Shape and Angular Distribution of the 4.438-MeV Line from Proton Inelastic Scattering off 12C

TL;DR

This study models the shape and angular distribution of the 4.438-MeV gamma-ray line from proton inelastic scattering off 12C, combining direct reaction and compound-nucleus mechanisms, and compares calculations with experimental data.

Contribution

It introduces a detailed theoretical framework that separately describes direct and compound-nucleus reaction mechanisms for gamma-ray line emission from proton-12C scattering.

Findings

Good agreement with data for proton energies 12-25 MeV using direct reaction models.

Lower energies require incoherent sums of direct and compound-nucleus contributions.

Potential applications to solar flare analysis and proton radiotherapy.

Abstract

The emission of the 4.438-MeV gamma-ray line in proton inelastic scattering off 12C has been investigated in detail. The correlated scattering and emission process is described independently for the direct reaction mechanism and for the compound-nucleus (CN) component. The inelastic scattering process for direct reactions is treated with a coupled-channels nuclear reaction code, while the CN component is described as a superposition of separate resonances with definite spin and parity, treated with the angular momentum coupling theory. The calculations are compared to a comprehensive data set on measured line shapes and angular distributions in the proton energy range E_p = 5.44 - 25.0 MeV. In the range E_p ~ 12 - 25 MeV a good agreement is obtained in calculations assuming direct reactions with only a negligible part of CN reactions. At lower energy, the data are reproduced by incoherent sums of the direct component with typically one CN resonance. Based on these results, the prospectives for line shape calculations applied to solar flares and gamma-ray emission in proton radiotherapy are discussed.