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Chapter 8 - Cosmic Radiation and Cosmogenic Radionuclides Chapter 8 Cosmic Radiation and Cosmogenic Radionuclides 158 European Atlas of Natural Radiation | Chapter 8 - Cosmic radiation and cosmogenic radionuclides Chapter 8 Cosmic radiation and cosmogenic radionuclides This chapter addresses the effects of cosmic radia- The next section addresses cosmogenic radionuclides. tion. Cosmic rays are atomic nuclei accelerated to high Concentration of cosmogenic radionuclides depends energy levels, thus creating electrons, gamma rays, on the interaction between cosmic radionuclide pro- neutrons and mesons when interacting with atmos- duction, decay, transport and deposit at the Earth´s pheric nuclei. surface. Examples of different cosmogenic radionu- clides are listed, along with illustrative applications Cosmic-radiation flux depends highly on altitude showing how measurements of cosmogenic radionu- above sea level. clides can be used. For example, specific radionuclides The intensity of cosmic radiation also depends on so- may be used to date soil sediments and ground water lar activity and variations in the geomagnetic field; in aquifers. Radionuclides are also useful for studying together with other factors, this triggers a 50 % varia- global climate change and air quality, thus making tion in production rates of cosmogenic radionuclides measurements important regionally and globally. on the Earth. Cosmogenic radionuclides are created Monitoring beryllium-7 (7Be) activity concentration is when cosmic rays interact with gases and particulate of special interest. This radioisotope is created in the matters in the Earth's atmosphere. stratosphere and in the upper troposphere, attaches The first section describes the rationale of the Annual to aerosols and is transported horizontally and verti- Cosmic-Ray Dose Map, which has been developed by cally by wind and gravity. Then it is removed from the the Joint Research Centre of the European Commis- atmosphere through the mechanism that also gov- sion. This map has a resolution of 1 km × 1 km and erns aerosols. Therefore, monitoring 7Be can greatly shows that the cosmic-ray dose mean value in Europe help in research on mass exchange between the strat- is about 390 microsievert (µSv). It also shows a strong osphere and troposphere as well as on local meteoro- correlation between dose and altitude, with the high- logical conditions. est dose levels occurring in the Alps, the Pyrenees and in eastern Turkey, all mountain regions.. The dose map section illustrates annual effective dose per capita per country; it shows that Turkey has the highest value (399 µSv/a) and Iceland the lowest (298 µSv/a), with an average of 334 µSv/a for the countries studied. Clockwise from top-left: NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 55 000 light-years in diameter and approximately 60 million light-years from Earth. Source: The Hubble Heritage Team (AURA/STScI/NASA)NASA Headquarters - Greatest Images of NASA (NASA-HQ-GRIN). Camerino hills: Sun on the hills, Camerino, Italy. Source: Ferdinando Cinelli. Monte Vettore sunrise: Sunrise, Monte Vettore, Sibillini Mountains National Park, Italy. Source: Ferdinando Cinelli. Camerino panorama: Panoramic viewpoint from Rocca dei Borgia, Camerino, Italy. Source: Ferdinando Cinelli. Sun during the Venus transit of June 2012. Source: Marc De Cort. Chapter 8 - Cosmic radiation and cosmogenic radionuclides | European Atlas of Natural Radiation 159 Cosmic radiation and cosmogenic radionuclides The Earth is constantly bombarded by high-energy cosmic-ray Typical concentrations (Bq/kg) particles which, upon entering the Earth’s atmosphere, interact Air Radionuclide Half-life Major radiations Target nuclides Rainwater Ocean water with its gaseous and particulate constituents to produce a (troposphere) variety of cosmogenic radioisotopes. This chapter presents and 10Be 1.6*106 a β N, O 2*10-8 describes the European Annual Cosmic-Ray Dose Map. It displays 26Al 7.2*105 a β+ Ar 2*10-10 the annual effective dose that a person may receive from cosmic 36Cl 3*105 a β Ar 1*10-5 rays at ground level. Moreover, the cosmogenic radionuclides 81Kr 2.3*105 a K X ray Kr will be described, focusing on their application as tracers in 14 3 -3 environmental studies. C 5.7*10 a β N, O 5*10 32 2 -7 The cosmic radiation is composed of penetrating ionising Si 1.7*10 a β Ar 4*10 radiation (both particulate and electromagnetic). By observing 39Ar 2.7*102 a β Ar 6*10-8 them, it has been established that cosmic rays are ordinary 3H 1.2*101 a β N, O 1.2*10-3 7*10-4 atomic nuclei accelerated to very high energy levels (e.g. Drury, 22Na 2.60 a β+ Ar 1*10-6 2.8*10-4 2012) which move through space at almost light speed. 35S 87.4 d β Ar 1.3*10-4 7.7-107*10-3 Depending on their origin, the cosmic rays vary greatly in their 7Be 53.3 d γ N, O 1*10-2 6.6*10-1 composition. Almost 90 % of cosmic rays are galactic in origin, 37Ar 35.0 d K X ray Ar 3.5*10-5 and are composed of high-energy particles (0.1 – 10 GeV) in the 33P 25.3 d β Ar 1.3*10-3 form of protons (87 %), helium nuclei (alpha particles, about 32P 14.3 d β Ar 2.3*10-4 12 %) and heavy nuclei (about 1 %) (Masarik & Beer, 1999). On 28Mg 20.9 h β Ar the contrary, solar cosmic rays, with lower energies (< 100 MeV), 24Na 15.0 h β Ar 3.0-5.9*10-3 have a much higher proton content (98 %) and lower alpha 38S 2.83 h β Ar 6.6-21.8*10-2 particle contribution (2 %), but do not have any heavier nuclei or 31Si 2.62 h β Ar energetic electrons. For the physical background and details, we 18F 110 min β+ Ar refer to Wissmann et al. (2005) and to Gaisser et al. (2016). 39 -1 The intensity of cosmic rays presents a wide variety of Cl 56.2 min β Ar 1.7-8.3*10 38 -1 timescales as well as spatial modulation in the Earth’s Cl 37.2 min β Ar 1.5-25*10 34m + atmosphere. Many field studies have been designed to assess Cl 32.0 min β Ar the understanding of spatial and temporal variations in cosmic Table 8-1. Cosmogenic radionuclides, induced in the Earth’s atmosphere by cosmic rays, rays in the heliosphere, and their relation to effects of the Sun listed in order of decreasing half-life. (e.g. Heber et al., 2013). The worldwide neutron monitor network Source: Eisenbud, 1997. (http://w3.nmdb.eu/), which is considered as a reliable network of ground-based detectors of cosmic rays, records many cosmic-ray n Top of atmosphere variations. 4n 2p (~35 km) 0 Variations in elevation and atmospheric conditions influence π + γ π + the amount of cosmic radiation received. The intensity of the e- α π + γ p e - cosmic-ray flux increases greatly as a function of altitude. At e- e+ π ν 6 – 9 km above the Earth’s surface, it is 30 times greater than at γ γ π+ - ground level (e.g. Monem, 2012). In addition, cosmic radiation is - + + + µ + e e - e π µ e n p partly screened and modulated by the Earth’s magnetic field and π 0 the atmosphere (Turekian & Graustein, 2003). The heliospheric γ k- environment considerably modulates the intensity of the cosmic γ n ν p - radiation reaching the Earth. On short timescales, Forbush + n n π e γ - n e p decreases (also known as Forbush effects) (Forbush, 1954) are π + - ν α alpha-particle sudden decreases in the intensity of cosmic radiation and in the n π amplitude of a few percent for several days. They occur after p n ν µ muon p + an increase in solar activity, such as coronal mass ejections. On + e positron - µ- µ- µ a longer timescale and with stronger influence, the intensity π+ π p e- electron ν n n of cosmic rays is influenced by the degree of solar activity th γ photon (gamma ray) e+ ν n ν k kaon and to variations in the geomagnetic field. Many studies have µ investigated and demonstrated the rigidity dependence of the nth π pion - n Air galactic cosmic-ray and solar activity (e.g. Dorman et al., 2001), e p proton reporting that high sunspot activities are highly correlated with n neutron γ low cosmic-ray intensity, and vice versa. In particular, the number ν neutrino Rock of sunspots, which can be considered an indicator of disturbances p in the Sun’s magnetic field, varies from year to year and exhibits n n n n p a nearly 11-year cycle. In this line, some works (e.g. Sloan & p n p ν Wolfendale, 2013; Stozhkov et al., 2017) cite solar activity, either directly or through its effect on cosmic rays, as an underestimated Electromagnetic Hadronic Mesonic Figure 8-1. contributor to global warming. component component component The cosmic ray cascade. Spallation reactions cause the formation of new All these factors may trigger variations of 50 % in production cosmogenic radionuclides in the atmosphere and in the lithosphere. Source: www.AntarcticGlaciers.org after Gosse & Phillips, 2001. rates of cosmogenic radionuclides on the Earth, which are radioactive isotopes produced and distributed within the Earth's Primary cosmic rays (mainly protons) are stable, charged By far, spallation is the most common mode of production of system. Cosmogenic activation strongly depends on the nucleon particles that have been accelerated to enormous energy levels cosmogenic radionuclides in the atmosphere; but other reactions flux, neutron-to-proton ratio and energies available. For instance, by astrophysical sources located somewhere in our universe.
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