Tutorial: Cosmic rays and the atmosphere

Stepan Poluianov, University of Oulu, Finland

Cosmic rays are high-energy nuclei of elements (hydrogen, helium and heavier species) travelling in space with relativistic speeds. The atmosphere of the Earth is constantly bombarded by them. When a cosmic ray particle enters the atmosphere, it likely experiences an interaction(s) with ambient atoms such as nitrogen, oxygen, argon and others. If the energy of the incident particle is high, the interaction can lead to a nuclear reaction with production of secondary particles. Those secondaries are often also highly energetic and are able to produce consequent reactions leading to production of even higher number of secondaries. Such chains of reactions form a cosmic-ray induced cascade also called as an air shower. The tutorial covers the topics of basics of the cascade formation, its composition and development over the altitude. It will be also explained what we can learn studying the cascade, particularly, with ground-based neutron monitors.