Photodisintegration of ultrahigh-energy cosmic rays by the universal radiation field

Abstract

We have carried out a detailed calculation to determine the effectiveness of the universal radiation field in disintegrating ultrahigh-energy cosmic-ray nuclei. We conclude that this process cannot lead to a pure-proton interpretation of the air-shower observations above 108 GeV. Photodisintegration by the universal radiation is unimportant on time scales of 1010 yr or less for helium nuclei below 1010 GeV and for iron nuclei below 1011-GeV total energy. Photodisintegration by dilute starlight photons in intergalactic space is unimportant on time scales of 1010 yr or less at all energies. © 1969 The American Physical Society.