Example for the “Empty Cascade” source class (isotropic luminosity L_γ = 10⁴⁹ erg s⁻¹ ) for injection of pure ⁵⁶Fe. Interaction rates (top left), particle densities in the source (top right), nuclear cascade (bottom left), and ejected cosmic ray fluence per shell (bottom right, without CMB and EBL interactions) as a function of the energy in the observer’s frame. The different curves in the right panels correspond to the different isotopes: primary ⁵⁶Fe in blue, secondaries produced in nuclear cascade according to legend, where the result from secondary nuclei other than nucleons are summed over. The other GRB parameters are chosen to be R ≃ 10^8.3 km, Γ = 300, ξ_Fe = 10, keV, and z = 2.