{"id":25704,"date":"2019-12-09T19:17:45","date_gmt":"2019-12-09T19:17:45","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=25704"},"modified":"2023-06-17T10:48:01","modified_gmt":"2023-06-17T10:48:01","slug":"cosmic-radiation-cosmic-rays","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/cosmic-radiation-cosmic-rays\/","title":{"rendered":"Cosmic Radiation – Cosmic Rays"},"content":{"rendered":"
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Cosmic Radiation<\/h2>\n
\"Cosmic<\/a>
Source: nasa.gov License: Public Domain<\/figcaption><\/figure>\n

Cosmic radiation<\/strong> refers to sources of radiation in the form of cosmic rays<\/strong> that come from the Sun or outer space. The earth has always been bombarded by high-energy particles originating in outer space that generate secondary particle showers in the lower atmosphere. Charged particles (especially high-energy protons) from the Sun and outer space interact with the earth\u2019s atmosphere and magnetic field to produce a shower<\/strong> of radiation (i.e., air shower), typically beta<\/a> and gamma radiation<\/a>. If you live at higher elevations or are a frequent airline passenger, this exposure can be significantly higher since the atmosphere is thinner here. The effects of the earth\u2019s magnetic field<\/strong> also determine the dose from cosmic radiation<\/strong>.<\/p>\n

At ground level, the muons<\/strong>, with energies mostly between 1 and 20 GeV, contribute about 75 % of the absorbed dose rate in free air. The remainder comes from electrons produced by the muons or present in the electromagnetic cascade. The annual cosmic ray dose<\/a> at sea level is around 0.27 mSv<\/strong> (27 mrem).<\/p>\n

Composition of Cosmic Radiation<\/h3>\n

The primary cosmic radiation<\/strong> consists of a mixture of high-energy protons<\/strong> (~87%), alpha particles<\/strong> (~11%), high-energy electrons<\/strong> (~1%), and a trace of heavier nuclei (~1%). The energy of these particles ranges between 108 <\/sup>eV and 1020<\/sup> eV. A very small fraction are stable particles of antimatter<\/a>, such as positrons<\/a> or antiprotons<\/a>. The precise nature of this remaining fraction is an area of active research.<\/p>\n

\"cosmic<\/a>Subsequently, a large number of secondary particles<\/strong>, in particular, neutrons<\/strong> and charged pions,<\/strong> are produced due to interactions between primary particles and the earth\u2019s atmosphere. Since pions are short-lived subatomic particles, the subsequent decay of the pions results in the production of high-energy muons<\/strong>. At ground level, the muons<\/strong>, with energies mostly between 1 and 20 GeV, contribute about 75 % of the absorbed dose rate<\/strong> in free air. The dose rate from cosmic radiation varies in different parts of the world and depends strongly on the geomagnetic field<\/strong>, altitude<\/strong>, and solar cycle<\/strong>. The cosmic radiation dose rate on airplanes is so high that, according to the United Nations UNSCEAR 2000 Report, airline flight crew workers receive more dose on average than any other worker, including those in nuclear power plants.<\/p>\n

We also have to include the neutrons at ground level. Cosmic rays interact with nuclei in the atmosphere and also produce high-energy neutrons<\/strong>. According to UNSCEAR, the fluency of neutrons is 0.0123 cm-2<\/sup>s\u20131<\/sup> at sea level for a geomagnetic latitude of 45 N. Based on this, the effective annual dose from neutrons at sea level and 50-degree latitude is estimated to be 0.08 mSv<\/strong> (8 mrem). The neutron flux measures higher in the vicinity of larger, heavier objects, e.g., buildings or ships. This effect is known as \u201ccosmic ray induced neutron signature\u201d or \u201cship effect,<\/strong>\u201d as it was first detected with ships at sea. Cosmic rays create showers in the atmosphere that include a broad spectrum of secondary neutrons, muons, and protons. The secondary neutrons may be of very high energy and induce spallation events in materials at ground level. Therefore in the vicinity of larger, heavier objects, these multiple neutrons produced in spallation events are referred to as \u201cship effect\u201d neutrons<\/strong>.<\/p>\n

Neutrons produced in the upper atmosphere are also responsible for the generation of radioactive carbon-14, which is the best-known cosmogenic radionuclide. Carbon-14<\/strong> is continuously formed in the upper atmosphere by interacting cosmic rays with atmospheric nitrogen. On average, one of every 1.3 x 1012<\/sup> carbon atoms in the atmosphere is a radioactive carbon-14 atom. As a result, all living biological substances contain the same amount of C-14 per gram of carbon, 0.3 Bq of carbon-14 activity per gram of carbon. As long as the biological system is alive, the level is constant due to the constant intake of all isotopes of carbon. When the biological system dies, it stops exchanging carbon with its environment, and from that point onwards, the amount of carbon-14 it contains begins to decrease as the carbon-14 undergoes radioactive decay.<\/p>\n

The energy of Cosmic Rays<\/h3>\n

The energies of the most energetic ultra-high-energy cosmic rays (UHECRs) have been observed to approach 3 x 1020<\/sup> eV, about 40 million times the energy of particles accelerated by the Large Hadron Collider. The origin of the high-energy particles is from outer space. It is assumed that particles with an energy up to about 1015<\/sup> eV are coming from our galaxy, whereas those with the highest energies probably have an extragalactic origin.<\/p>\n

Classification of Cosmic Radiation<\/h2>\n

Cosmic radiation can be divided into different types according to its origin. There are three main sources of such radiation:<\/p>\n