Emissivities of γ-rays from decays of π⁰-mesons produced in pp interactions.Different line styles are calculated for three distributions of accelerated protons: (1) red dashed: power-law in momentum with α_p = 2.0, (2) black dashed: power-law in momentum with α_p = 2.85, (3) black solid: power-law in kinetic energy with α_p = 2.85, respectively. The proton spectra are normalised in a way that the energy density w_p (≥ 1 GeV) = 1 eV cm⁻³. The density of the hydrogen gas n_H = 1 cm⁻³.