Secondary Cosmic Ray Particles
When cosmic rays enter the Earth's atmosphere they collide with molecules, mainly oxygen and nitrogen. The interaction produce a cascade of lighter particles, a so-called air shower. All of the produced particles stay within about one degree of the primary particle's path. Typical particles produced in such collisions are neutrons, charged mesons e.g. positive and negative pions and kaons. Some of these subsequently decay into muons, which are able to reach the surface of the Earth, and even penetrate for some distance into shallow mines. The muons can be easily detected by many types of particle detectors, such as cloud chambers, bubble chambers or scintillation detectors. Several muons observed by separated detectors at the same instant indicates that they have been produced in the same shower event.
Cosmic rays impacting other planetary bodies in the Solar System are detected indirectly by observing high energy gamma ray emissions by gamma-ray telescope. These are distinguished from radioactive decay processes by their higher energies above about 10 MeV.
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