A Model of Galactic Cosmic Ray Propagation in the Interstellar Medium A Model of Galactic Cosmic Ray Propagation in the Interstellar Medium Cosmic rays are fully ionized nuclei with energies that follow a power law spectrum. The range of Z values cover nearly the entire periodic table but the lighter species such as hydrogen and helium dominate over all else.
Most cosmic rays come from outside the solar system.
Current theory hold that they are generated by various sources within the galaxy and then accelerated by some unknown process. Supernova shock waves are one possible mechanism for this acceleration. The galactic magnetic field confines most of these particles which circulate for about 10 million years. During that time they will interact with the interstellar medium which contains trace amounts of hydrogen and helium. These interactions slow the nuclei down through ionizational energy loss and change the overall composition through nuclear spallation.