Histogram of 100 MeV protons propagating in a stratified medium: Morlino et al. (2015) model. The top two and bottom two plots refer to the diffuse region, n = 100 cm⁻³, and the third and fourth plots are for the dense embedded region, n = 300 cm⁻³. Note that in the top and bottom panel, which show the distribution in the external medium, the low-energy flat spectrum is from protons that escape after partial trapping in the denser stratum. See also Figs. 7 and 8.