NATURE OF THE HIGHEST ENERGY COSMIC-RAYS

Ultrahigh energy gamma rays produce electron-positron pairs in interac tions on the geomagnetic field. The pair electrons suffer magnetic bre msstrahlung and the energy of the primary gamma ray is shared by a bun ch bf lower energy secondaries. These processes reflect the structure of the geomagnetic field and cause experimentally observable effects. The study of these effects with future giant air shower arrays dan ide ntify the nature of the highest energy cosmic rays as either gamma ray s or nuclei.