Cosmic radiation interactions

Kr Cosmic radiation interacting with the atmosphere. 104 to 108 years... 

We are constantly exposed to background radiation from cosmic radiation (interaction of energy from the sun with the earth s atmosphere), terrestrial radiation from breakdown of uranium in the soil, and natural internal radiation in our bodies from carbon-14 that is present at birth. Man-made radiation sources include diagnostic X-rays, nuclear medicine (bone scans, thyroid scans, etc.), radiation therapy for cancer, nuclear power facilities, and nuclear weapons. 

Background Radiation. If the radiation from a radioactive source is measured, the spectmm also includes contributions from the radiations from the surrounding environment. This includes radiations from the radioactivity in the materials in and around the detector, including the stmcture of the building or nearby earth. There is also cosmic radiation that comes from space and interacts with the earth and atmosphere to produce radiations that may enter the detector, and thus is observed. 

Carbon-14 is produced in the atmosphere by the interaction of neutrons from cosmic radiation with ordinary nitrogen atoms ... 

A large number of radionuclides are produced continuously in the upper atmosphere through various interactions between gases and cosmic radiation [9,10]. Some of these radionuclides are produced also in the soil and bodies of surface water by cosmic radiation that penetrates the earth s atmosphere to interact with materials at the surface of the earth. Radionuclides which are of hydrologic interest and which are also produced primarily in the atmosphere (prior to 1945) are listed in Table 1. 

In addition to these stable isotopes, many elements have one or more radioactively unstable isotopes, which are produced either as a result of specific nuclear processes (such as 14C, which is the result of the interaction of neutrons produced by cosmic radiation with 14N in the atmosphere) or as daughter... 

The cosmic radiation incident on the earth is generated in our galaxy. It is effectively absorbed in the atmosphere, and the flux density is reduced from about 20 cm s to about 1 cm" s at the surface of the earth. By interaction with the atoms and the molecules in the atmosphere showers of elementary particles are produced, making up the secondary cosmic radiation. Positrons, muons, several kinds of mesons and baryons were first detected in the secondary cosmic radiation. Furthermore, nuclear reactions induced by secondary cosmic radiation lead to the production of cosmogenic radionuchdes, such as T and (section 1.2). 

Energetic particles of the galactic cosmic radiation (GCR) have a mean penetration depth in rock of about 50 cm, comparable to the typical size of a meteorite. GCR-induced effects therefore provide a means to study the history of meteorites as small objects in space or in the top few meters of their parent body. These effects include cosmic ray tracks, i.e., the radiation damage trails in a crystal lattice produced by heavy ions in the GCR (Fleischer et al. 1975), and thermoluminescence, i.e., the light emitted by a heated sample which had been irradiated by energetic particles (Benoit and Sears 1997). By far most important, however, are cosmogenic nuclides, produced by interactions of primary and secondary cosmic ray particles with target atoms. 

Primary cosmic radiation, in the form of high energy nuclear particles, electrons rmd photons from outside the soleU system and from the Sun, continueJly homheU ds our atmosphere. Secondary radiation, resulting from the interaction of the primeuy cosmic rays with atmospheric gas, is present at sea-level rmd throughout the atmosphere. 

When cosmic rays interact with living tissue, they produce radiation dcimage. The eimount of the dcimage depends on the toted dose of radiation. At sea level, this dose is smedl compeU ed with doses from other sources but both the quemtity emd quedity of the radiation change rapidly with edtitude. Approximate dose rates under VeU ious conditions are ... 

Most of the cosmic ray energy (>98%) is dissipated in the earth s atmosphere in the nuclear reactions they produce. The atmospheric column represents about 13 mean free paths for nuclear interactions of fast protons and neutrons. After traversal through the atmosphere, the secondary particles of the cosmic radiation continue to produce nuclear reactions with the surficial terrestrial reservoirs the hydrosphere. 

The previously cited sum peaks occur for two or more coincident gamma rays, for example, at 2505 keV for °Co. Interactions outside the detector commonly are detected as a peak at 511 keV due to annihilation radiation and at about 200 keV due to Compton scattering at 180°. Gamma rays produced by cosmic-ray interactions in or near the detector are observed as discussed in Section 8.2.2. 

Radionuchdes produced from cosmic-energy interactions are usually formed high in the atmosphere where cosmic radiation is most intense. The spatial variabihty of these radionuclides is partly due to variation in the dux of cosmic radiation, which varies spatially with altitude and latitude and temporally with changes in cosmic-ray production rates. For example, the latitudinal production rate between the poles and the equator varies by about a factor of 4, and production rates of some radionuclides have varied by about 10% over the past 10 million yr. There are only a few radionuclides that are formed in sufficient quantities and are long-lived enough to contribute to the... 

Primary cosmic rays interact with the upper atmosphere to produce mesons (mostly ir mesons) and nucleons. Many p mesons (or muons), produced as decay products of ir-mesons during their passage through the air, constitute most of the cosmic radiation found in the lower atmosphere (Friedlander and others, 1964). 

Cosmogenic radionuclides are produced continuously as a result of nuclear reaction in the environment, such as interaction with cosmic radiation, spallation, and natural fission. A partial list is presented in Table 2. 

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