A large number of radionuclides are produced in the terrestrial atmosphere as a result of nuclear reactions involving cosmic rays. These comprise very energetic radiation falling upon the Earth from outer space and consisting mainly of charged particles of which the majority are probably protons, although alpha particles and electrons are also present. There is some evidence that approximately 2% of the primary radiation consists of heavy atomic nuclei. Cosmic rays originate from the Sun as well as from galactic sources. Their flux depends upon the kinetic energies of their components which may be as great as 102 GeV (1 GeV = 109 eV); it appears that about half of the flux has a value between 0·5 and 5 GeV.
KeywordsTree Ring Isotope Fractionation Radiocarbon Date Proton Flux Precipitate Calcium Carbonate
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