Cosmic Ray
Cosmic rays are high speed, i. e. high energy particles, mainly originating in outer space, outside the Solar system. They may produce showers of secondary particles that penetrate the Earth's atmosphere and sometimes even Earth's surface.
The term ray is historical as cosmic rays were thought to be electromagnetic radiation.
Most primary cosmic rays are composed of well known, stable subatomic particles that normally occur on Earth, such as protons, other atomic nuclei, or electrons. About 90% of cosmic rays are simple protons, i. e. hydrogen nuclei; 9% are helium nuclei or alpha particles, and 1% are the nuclei of heavier elements. These nuclei constitute 99% of the cosmic rays. Solitary electrons (similar to beta particles) constitute much of the remaining 1%. A very small fraction are stable particles of antimatter, such as positrons or antiprotons, and the precise nature of this remaining fraction is an area of active research.
Read more about Cosmic Ray: Introduction, Primary Cosmic Rays, Secondary Cosmic Ray Particles, Detection By Particle Track-etch Technique, Research and Experiments, History
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