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    Cosmic Rays
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    Cosmic Ray Background


    Cosmic rays are particles from outer space that have a lot of energy. Most of these particles are protons, but some of them are helium nuclei or electrons. Cosmic rays are not actually rays but particles that are moving very fast.

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    Cosmic rays are energetic particles originating from outer space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are protons, almost 10% are helium nuclei (alpha particles), and slightly under 1% are heavier elements and electrons (beta minus particles). The term ray is a misnomer, as cosmic particles arrive individually, not in the form of a ray or beam of particles.

    The variety of particle energies reflects the wide variety of sources. The origins of these particles range from energetic processes on the Sun all the way to as yet unknown events in the farthest reaches of the visible universe. Cosmic rays can have energies of over 1020 eV, far higher than the 1012 to 1013 eV that man-made particle accelerators can produce. (See Ultra-high-energy cosmic rays for a description of the detection of a single particle with an energy of about 50 J, the same as a well-hit tennis ball at 42 m/s [about 94 mph].) There has been interest in investigating cosmic rays of even greater energies.

    In high-energy physics, an ultra-high-energy cosmic ray (UHECR) or extreme-energy cosmic ray (EECR) is a cosmic ray (subatomic particle) which appears to have extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays. These particles are significant because they have energy comparable to (and sometimes exceeding) the Greisen–Zatsepin–Kuzmin limit.

    Galactic cosmic rays (GCRs) consist of those cosmic rays that enter the solar system from the outside. They are high-energy charged particles composed of protons, electrons, and fully ionized nuclei of light elements and are a strong source for cosmic ray spallation in the atmosphere of the earth.

    Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from stray electrons to alpha particles. These cause spallation when a cosmic ray (e.g. a proton) impacts with matter, including other cosmic rays. The result of the collision is the expulsion of large members of nucleons (protons and neutrons) from the object hit. This process goes on not only in deep space, but in our upper atmosphere due to the impact of cosmic rays.

    The health threat from cosmic rays is the danger posed by cosmic rays generated by the Sun and other stars to astronauts on interplanetary missions. Cosmic rays consist of high energy protons and other nuclei. They are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.

    A Cosmic-ray observatory is a scientific installation built to detect high-energy-particles coming from space called Cosmic rays. It is not yet possible to build a Cosmic ray image forming optics, like a Wolter telescope for lower energy X-rays, although some Cosmic-ray observatories also look for x-rays. Ultra-high-energy cosmic-rays (UHEC) pose further detection problems.

    Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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    Last updated: June 2013
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