Ionisation rate per H₂ due to primary and secondary CR species, ζ, plotted vs. the surface density Σ (bottom scale) and the column density N (top scale). The black line shows the total ionisation rate. Partial contributions to ζ include ionisation due to primary CR protons and electrons (blue and red lines, respectively), ionisation due to secondary electrons created by primary CRs (orange line), and ionisation due to electrons and positrons created by charged pion decay and pair production (green line). The blue dashed line shows the proton contribution calculated with the CSDA approach. The horizontal dashed line at 1.4 × 10⁻²² s⁻¹ indicates the total ionisation rate set by long-lived radioactive nuclei (LLR). For comparison, we also plot the total ionisation rate per H₂ obtained by (Umebayashi & Nakano 1981; grey dashed line). The total rate of the electron production, ζ_e, is approximately 1.11ζ.