galactic cosmic ray

Galactic cosmic rays (GCRs) are high-speed particles, primarily atomic nuclei or electrons, originating from within the Milky Way Galaxy. These particles travel through space at speeds approaching that of light. When GCRs reach Earth's atmosphere, they collide with atmospheric nuclei, creating secondary particles that are then observed at ground level.12

The composition of GCRs varies with energy. At higher energies, they are predominantly protons (hydrogen nuclei) and alpha particles (helium nuclei), with a smaller percentage of electrons and heavier atomic nuclei. The trajectories of lower-energy cosmic rays are influenced by Earth's magnetic field, leading to energy cutoffs depending on geomagnetic latitude. Solar activity also affects the flux of low-energy cosmic rays, with increased solar activity correlating with decreased cosmic radiation reaching Earth.1

The origins of GCRs are inferred from their elemental and isotopic abundances. It is believed that heavier cosmic rays are produced in energetic events like supernova explosions. Studying cosmic rays has been crucial in the development of particle physics, leading to the discovery of fundamental subatomic particles.1