Energy-loss lengths of (a) γ-rays and (b) electrons, interacting with CMB and EBL (R. C. Gilmore et al. 2012) photons. Note that the interaction length for IC scattering differs from the energy-loss length ﹩{\lambda }_{{\rm{IC}}}=c{\gamma }_{e}/| {\dot{\gamma }}_{e}| ﹩ shown here. For triplet-pair production, we assume a conservative inelasticity of η = 0.5. The gray dashed and solid lines correspond to synchrotron radiation in magnetic-field strengths of 1 and 10 nG. γ-ray attenuation with the cosmic radio background occurs at ≳10²⁰ eV. IC losses on the radio background (R. J. Protheroe & P. L. Biermann 1996) are negligible compared with IC losses on the CMB and synchrotron losses for the parameter range considered here.