On cosmic-ray interactions with photons

Various effects of high-energy cosmic-ray interactions with cosmic blackbody radiation are considered, particularly the cutoff of the cosmic-ray energy spectrum at [Formula: see text] for protons, and at [Formula: see text] for α particles and other nuclei, as a consequence of photo-production of pions and photodisintegration of nuclei.If quasars and similar objects are indeed the source of high-energy cosmic rays, the protons and nuclei of energy E > (3–10) × 1015 eV would encounter considerable difficulty in being injected from these sources because of interactions with photons, with the result that: (1) the cosmic-ray flux with energy above [Formula: see text] to 3 × 1016 eV may have predominantly proton composition, (2) the cosmic-ray flux may have steeply decreasing intensity in the energy ranpe E = (3–30) × 1015 eV.