Cosmic ray

From Simple English Wikipedia, the free encyclopedia

Cosmic rays are very high-energy radiation, mostly from outside the Solar System.[1]

The term ray is a historical accident, as cosmic rays were at first, and wrongly, thought to be mostly electromagnetic radiation.

They are particles. Most are protons and alpha particles, which are the nuclei of helium atoms. Some are electrons (beta particles), gamma rays or photons and a tiny fraction are even heavier particles.

Origin[change | change source]

Their origin is not exactly known. There is evidence that many primary cosmic rays come from the supernovae of massive stars.[2] However, this is not thought to be their only source. Active galactic nuclei probably also produce cosmic rays. Galactic cosmic rays are Particles trapped in the magnetic field of Earth, Particles sent flying into space during a solar flare, and High-energy protons and heavy ions that originate outside our solar system

Secondary cosmic rays[change | change source]

Cosmic rays can have as much energy as 1020 eV, far higher than the 1012 to 1013 eV that man-made particle accelerators can produce. When cosmic ray particles enter the Earth's atmosphere they hit other particles, like molecules of oxygen and nitrogen. This causes a shower of lighter particles, a so-called 'air shower'.

The number of particles made in an air shower event can reach billions. All of the particles in the shower stay within about one degree of the first particle's path. In a shower are x-rays, muons, protons, alpha particles, pions, electrons, and neutrons.[3]

Typical particles produced in such collisions are neutrons and charged mesons such as positive or negative pions and kaons. Some of these decay into muons. These 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. The observation of a secondary shower of particles in different detectors at the same time shows that all of the particles came from that event. Several cosmic-ray observatories have been built to detect and study cosmic rays.

Practical importance[change | change source]

Effects on Earth chemistry[change | change source]

Cosmic rays are responsible for the continuous production of certain unstable isotopes in the Earth's atmosphere, such as carbon-14, by the reaction:

n + 14N → p + 14C

Cosmic rays kept the level of carbon-14 in the atmosphere roughly constant (70 tons) for at least the past 100,000 years, until the beginning of above-ground nuclear weapons testing in the early 1950s.[4] This is an important fact used in radiocarbon dating used in archaeology.

Effect on space vehicles[change | change source]

Cosmic rays are of great practical interest, because they can damage microelectronics and life outside the protection of the Earth's atmosphere and magnetic field.[5]

References[change | change source]

  1. Sharma (2008). Atomic and nuclear physics. Pearson Education India. p. 478. ISBN 978-81-317-1924-4.
  2. Ginger Pinholster (2013). "Evidence shows that cosmic rays come from exploding stars".
  3. Morison, Ian (2008). Introduction to astronomy and cosmology. John Wiley & Sons. p. 198. ISBN 978-0-470-03333-3.
  4. Trumbore, Susan (2000). "Radiocarbon Geochronology". In In Noller J.S; Sowers J.M.& Lettis W.R (ed.). Quaternary geochronology: methods and applications. Washington, D.C.: American Geophysical Union. pp. 41–59. ISBN 0-87590-950-7. Archived from the original on 2013-05-21. Retrieved 2014-06-29.{{cite book}}: CS1 maint: multiple names: editors list (link)
  5. Nerlich, Steve (2011). "Astronomy without a telescope – Oh-My-God particles". Universe Today. Universe Today. Retrieved 17 February 2013.