COSMIC-RAYS OF SUPERHIGH AND ULTRAHIGH ENERGIES

We present a review and analysis of the experimental data on cosmic rays with energies above 10(14)-10(15) eV and up to 10(20) eV. At the beginning a brief survey of the direct experimental data on the cosmic-ray energy spectrum and mass composition is given. We then consider the choice of the hadron interaction model at energies above 10(15) eV that is essential for the interpretation of the experimental data on extensive air showers (EAS). Much attention is given to the well known knee in the primary energy spectrum at similar to 3 x 10(15) eV and also to an analysis of this phenomenon in the framework of the recently developed Hall diffusion model. In doing so we use as yet scarce data on cosmic-ray anisotropy and mass composition at superhigh energies 10(14)-10(17) eV. A considerable part of our review is concerned with cosmic rays of ultrahigh energies 10(17)-10(20) eV. Using the galactic origin model for cosmic rays with energies 10(14)-10(20) eV the possibility of explaining all the relevant data at energies above 3 x 10(18)-10(19) eV is discussed: evidence of the 'ankle' in the primary energy spectrum, the upper bound of cosmic-ray anisotropy, and evidence for the increasing proton abundance. The prospects for future cosmic-ray investigations at superhigh energies are outlined and the great importance of development in the neutron and proton astronomy for energies above 10(18)-10(19) eV is pointed out.