Emissivities of γ-rays from decays of π⁰-mesons produced in pp (solid lines) and ¹⁶O¹⁶O (cyan dashed lines) interactions for two energy distributions of particles: power-law in kinetic energy, T^−α with α = 2 and α = 2.85 (for both p and ¹⁶O projectiles). Also plotted is the total γ-rays produced in ¹⁶O¹⁶O (red dashed lines) interactions, including the hard photon channel. The emissivities of γ-rays are shown in arbitrary units and are normalised at 1 GeV to demonstrate the differences between the spectra of γ-rays from two reactions.