Chapter 5 - Primary Cosmic Radiation

Abstract

This chapter describes primary cosmic radiation. The term cosmic radiation usually means the flux of energetic particles that enter the Earth's atmosphere from outer space. The bulk of this radiation is of hadronic nature and seems to be of galactic origin however, the ultra energetic tail of the spectrum with energies in excess of about 109 GeV is probably of extragalactic origin. The low energy portion of the cosmic ray spectrum is subject to strong variability because of solar modulation. The solar contribution to the local cosmic radiation frequently referred to as “solar cosmic rays”, “energetic solar particles” (ESP) or “solar energetic particles” (SEP), concerns the very low energy portion of the spectrum only (“E” < 50 MeV) and is of sporadic nature. The sources of energetic solar particles are usually “solar flare events”. It is mostly protons and electrons that are ejected but small quantities of heavier elements may be involved. The hadronic component covers an enormous energy range. The chemical (or mass) composition of the hadronic component ranges from protons to the actinide elements, and seems to manifest non-trivial energy dependence. The flux of antinuclei from cosmic ray interactions with the interstellar medium is estimated to be approximately a factor of 10-8 lower than the flux of antiprotons.