Final answer:
The main component of primary cosmic rays are hydrogen nuclei, or protons, which account for nearly 90% of these particles.
Step-by-step explanation:
The main component of primary cosmic rays is hydrogen nuclei (protons).
Cosmic rays are high-energy particles that originate from outside our solar system and are composed primarily of atomic nuclei and electrons. Almost 90% of these particles are protons, which are hydrogen nuclei stripped of their electrons. Roughly another 9% consist of helium nuclei and heavier elements. The remaining particles include electrons and positrons, with positrons having the same mass as electrons but possessing a positive charge.
Cosmic rays often reach speeds of up to 90% the speed of light and are believed to be produced by phenomena such as supernova explosions which generate shock waves that can accelerate these particles. Additionally, cosmic rays carry important information about the origins and the composition of our universe as they mirror the abundances of elements present in stars and interstellar gas.