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Cosmic ray

Cosmic ray

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Cosmic rays are energetic particles originating from outer space
Outer space
Outer space comprises the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace and terrestrial locations....

 that impinge on Earth's atmosphere
Earth's atmosphere
The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

. Almost 90% of all the incoming cosmic ray particles are proton
Proton
The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+...

s, almost 10% are helium
Helium
Helium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...

 nuclei (alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as or . They have a net spin of zero, and normally a total energy of about 5 MeV...

s), and slightly under 1% are heavier elements and electron
Electron
An electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. An electron has a mass that is approximately 1836 times less than that of the proton. The intrinsic angular momentum of the electron is a half integer...

s (beta minus particle
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...

s). The term ray is a misnomer, as cosmic particles arrive individually, not in the form of a ray or beam of particles.

The variety of particle energies reflects the wide variety of sources. The origins of these particles range from energetic processes on the Sun
Sun
The Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....

 all the way to as yet unknown events in the farthest reaches of the visible universe
Universe
The Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...

. Cosmic rays can have energies of over 1020 eV
Electronvolt
In physics, the electron volt is a unit of energy. By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electrostatic potential difference of one volt...

, far higher than the 1012 to 1013 eV that man-made particle accelerators can produce. (See Ultra-high-energy cosmic ray
Ultra-high-energy cosmic ray
In high-energy physics, an ultra-high-energy cosmic ray or extreme-energy cosmic ray is a cosmic ray which appears to have extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays...

s for a description of the detection of a single particle with an energy of about 50 J, the same as a well-hit tennis ball at 42 m/s [about 94 mph].) There has been interest in investigating cosmic rays of even greater energies.


Composition


Cosmic rays may broadly be divided into two categories, primary and secondary.
The cosmic rays that arise in extrasolar astrophysical sources are primary cosmic rays; these primary cosmic rays can interact with interstellar matter
Interstellar medium
In astronomy, the interstellar medium is the gas and dust that pervade interstellar space: the matter that exists between the star systems within a galaxy. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

 to create secondary cosmic rays. The sun also emits low energy cosmic rays associated with solar flare
Solar flare
A solar flare is a large explosion in the Sun's atmosphere that can release as much as 6 × 1025 joules of energy. The term is also used to refer to similar phenomena in other stars, where the more accurate term stellar flare applies....

s. The exact composition of primary cosmic rays, outside the Earth's atmosphere
Earth's atmosphere
The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

, is dependent on which part of the energy spectrum
Energy spectrum
An energy spectrum is a distribution energy among a large assemblage of particles. It is a statistical representation of the wave energy as a function of the wave frequency, and an empirical estimator of the spectral function...

 is observed. However, in general, almost 90% of all the incoming cosmic rays are proton
Proton
The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+...

s, about 9% are helium
Helium
Helium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...

 nuclei (alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as or . They have a net spin of zero, and normally a total energy of about 5 MeV...

s) and about 1% are electron
Electron
An electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. An electron has a mass that is approximately 1836 times less than that of the proton. The intrinsic angular momentum of the electron is a half integer...

s. The ratio of hydrogen to helium (28% by mass He) is about the same as the primordial elemental abundance ratio of these elements (24% by mass He) in the universe.

The remaining fraction is made up of the other heavier nuclei which are abundant end products of stars' nuclear synthesis. Secondary cosmic rays consist of the other nuclei which are not abundant nuclear synthesis end products, or products of the Big Bang
Big Bang
The Big Bang is the cosmological model of the initial conditions and subsequent development of the Universe that is supported by the most comprehensive and accurate explanations from current scientific evidence and observation...

, primarily lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number three. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

, beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4.A bivalent element, beryllium is found naturally only combined with other elements in minerals. Notable gemstones which contain beryllium include Beryl and Chrysoberyl...

 and boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a trivalent metalloid element which occurs abundantly in the evaporite ores borax and ulexite....

. These light nuclei appear in cosmic rays in much greater abundance (about 1:100 particles) than in solar atmospheres, where their abundance is about 10−7 that of helium
Helium
Helium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...

.

This abundance difference is a result of the way secondary cosmic rays are formed. When the heavy nuclei components of primary cosmic rays, namely the carbon and oxygen nuclei, collide with interstellar matter, they break up into lighter nuclei (in a process termed cosmic ray spallation
Cosmic ray spallation
Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from stray electrons to alpha particles....

), into lithium, beryllium and boron. It is found that the energy spectra of Li, Be and B fall off somewhat more steeply than those of carbon or oxygen, indicating that less cosmic ray spallation
Cosmic ray spallation
Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from stray electrons to alpha particles....

 occurs for the higher energy nuclei presumably due to their escape from the galactic magnetic field. Spallation is also responsible for the abundances of Sc, Ti, V and Mn elements in cosmic rays, which are produced by collisions of Fe and Ni nuclei with interstellar matter
Interstellar medium
In astronomy, the interstellar medium is the gas and dust that pervade interstellar space: the matter that exists between the star systems within a galaxy. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

; see Environmental radioactivity#Natural.

In the past, it was believed that the cosmic ray flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as the amount that flows through a unit area per unit time...

 has remained fairly constant over time. Recent research has, however, produced evidence for 1.5 to 2-fold millennium-timescale changes in the cosmic ray flux in the past forty thousand years.

Modulation


The flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as the amount that flows through a unit area per unit time...

 (flow rate) of cosmic rays incident on the Earth’s upper atmosphere is modulated (varied) by two processes; the sun’s solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time...

 and the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is approximately a magnetic dipole, with the magnetic field S pole near the Earth's geographic north pole and the other magnetic field N pole near the Earth's geographic south pole...

. Solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time...

 is expanding magnetized plasma
Plasma (physics)
In physics and chemistry, plasma is a partially ionized gas, in which a certain proportion of electrons are free rather than being bound to an atom or molecule. The ability of the positive and negative charges to move somewhat independently makes the plasma electrically conductive so that it...

 generated by the sun, which has the effect of decelerating the incoming particles, as well as excluding some of the particles with energies below about 1 GeV. The amount of solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons with energies of about 1 keV. The stream of particles varies in temperature and speed with the passage of time...

 is not constant due to changes in solar activity, for instance over its regular eleven-year cycle. Hence the level of modulation varies in anticorrelation with solar activity. Also the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is approximately a magnetic dipole, with the magnetic field S pole near the Earth's geographic north pole and the other magnetic field N pole near the Earth's geographic south pole...

 deflects some of the cosmic rays, giving rise to the observation that the intensity of cosmic radiation is dependent on latitude
Latitude
Latitude, usually denoted by the Greek letter phi gives the location of a place on Earth north or south of the equator. Lines of Latitude are the imaginary horizontal lines shown running east-to-west on maps that run either north or south of the equator...

, longitude
Longitude
Longitude , identified by the Greek letter lambda , is the geographic coordinate most commonly used in cartography and global navigation for east-west measurement...

 and azimuth
Azimuth
An Azimuth is the angle from a reference vector in a reference plane to a second vector in the same plane, pointing toward, , something of interest. For example, with the sea as your reference plane, the azimuth of the Sun might be the angle between due North and the point on the horizon the Sun...

. The cosmic flux varies from eastern and western directions due to the polarity of the Earth’s geomagnetic field and the positive charge dominance in primary cosmic rays; this is termed the east-west effect. The cosmic ray intensity at the equator is lower than at the poles as the geomagnetic cutoff value is greatest at the equator. This is because charged particles tend to move in the direction of field lines and not across them, so that they are concentrated in the polar regions (where field lines are closest together). This is the reason the aurorae
Aurora (astronomy)
Auroras, sometimes called the northern and southern lights or aurorae , are natural light displays in the sky, usually observed at night, particularly in the polar regions. They typically occur in the ionosphere. They are also referred to as polar auroras...

 occur at the poles, since the field lines curve down towards the Earth’s surface there. Finally, the longitude
Longitude
Longitude , identified by the Greek letter lambda , is the geographic coordinate most commonly used in cartography and global navigation for east-west measurement...

 dependence arises from the fact that the geomagnetic dipole
Dipole
In physics, there are two kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some, usually small, distance. A permanent electric dipole is called an...

 axis is not parallel to the Earth’s rotation axis.

This modulation which describes the change in the interstellar intensities of cosmic rays as they propagate in the heliosphere
Heliosphere
The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind...

 is highly energy and spatial dependent, and it is described by the Parker's Transport Equation in the heliosphere. At large radial distances, far from the Sun (~94 AU
Astronomical unit
An astronomical unit is a unit of length roughly equal to the mean distance between the Earth and the Sun. It is approximately 150 million kilometres ....

), there exists the region where the solar wind undergoes a transition from supersonic to subsonic speeds called the solar wind termination shock. The region between the termination shock and the heliopause (the boundary marking the end of the heliosphere) is called the heliosheath. This region acts as a barrier to cosmic rays, decreasing their intensity at lower energies by about 90%; thus it is not only the Earth's magnetic field
Magnetic field
Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges...

 that protects us from cosmic ray bombardment.

From a modelling
Scientific modelling
Scientific modelling is the process of generating abstract, conceptual, graphical and/or mathematical models. Science offers a growing collection of methods, techniques and theory about all kinds of specialized scientific modelling....

 point of view, there is a challenge in determining the Local Interstellar Spectra
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

 (LIS) due to large adiabatic energy changes these particles experience owing to the diverging solar wind in the heliosphere. However, significant progress has been made in the field of cosmic ray studies with the development of an improved state-of-the-art 2D numerical model that includes the simulation of the solar wind termination shock, drifts and the heliosheath coupled with fresh descriptions of the diffusion tensor, see Langner et al. (2004). But challenges also exist because the structure of the solar wind and the turbulent magnetic field in the heliosheath is not well understood indicating the heliosheath as the region unknown beyond. With lack of knowledge of the diffusion coefficient perpendicular to the magnetic field our knowledge of the heliosphere and from the modelling point of view is far from complete. There exist promising theories like ab initio
Ab initio quantum chemistry methods
Ab initio quantum chemistry methods are computational chemistry methods based on quantum chemistry. The term ab initio indicates that the calculation is from first principles and that no empirical data is used...

 approaches, but the drawback is that such theories produce poor compatibility with observations (Minnie, 2006) indicating their failure in describing the mechanisms influencing the cosmic rays in the heliosphere.

Detection


The nuclei that make up cosmic rays are able to travel from their distant sources to the Earth because of the low density of matter in space. Nuclei interact strongly with other matter, so when the cosmic rays approach Earth they begin to collide with the nuclei of atmospheric gases. These collisions, in a process known as a shower
Particle shower
In particle physics, a shower is a cascade of secondary particles produced as the result of a high-energy particle interacting with dense matter. The incoming particle interacts, producing multiple new particles with lesser energy; each of these then interacts in the same way, a process that...

, result in the production of many pion
Pion
In particle physics, a pion is any of three subatomic particles: , and . Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force.-Basic properties:...

s and kaon
Kaon
In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...

s, unstable meson
Meson
In particle physics, mesons are subatomic particles composed of one quark and one antiquark. They are part of the hadron particle family—particles made of quarks. The other members of the hadron family are the baryons—subatomic particles composed of three quarks...

s which quickly decay into muon
Muon
The muon is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the tauon, and the three neutrinos, it is classified as a lepton. It is the unstable subatomic particle with the second longest mean lifetime , behind the neutron...

s. Because muons do not interact strongly with the atmosphere and because of the relativistic effect of time dilation
Time dilation
Time dilation is a phenomenon described by the theory of relativity. It can be illustrated by supposing that two observers are in motion relative to each other, and/or differently situated with regard to nearby gravitational masses. They each carry a clock of identically similar construction and...

 many of these muons are able to reach the surface of the Earth. Muons are ionizing radiation
Ionizing radiation
Ionizing radiation consists of subatomic particles or electromagnetic waves that are energetic enough to detach electrons from atoms or molecules, ionizing them. The occurrence of ionization depends on the energy of the impinging individual particles or waves, and not on their number...

, and may easily be detected by many types of particle detectors such as bubble chamber
Bubble chamber
A bubble chamber is a vessel filled with a superheated transparent liquid used to detect electrically charged particles moving through it. It was invented in 1952 by Donald A. Glaser, for which he was awarded the 1960 Nobel Prize in Physics...

s or scintillation
Scintillation (physics)
Scintillation is a flash of light produced in a transparent material by an ionization event. See scintillator and scintillation counter for practical applications.-Overview:...

 detectors. If several muons are observed by separated detectors at the same instant it is clear that they must have been produced in the same shower event.

Detection by particle track-etch technique


Cosmic rays can also be detected directly when they pass through particle detectors flown aboard satellites or in high altitude balloons. In a pioneering technique developed by P. Buford Price
P. Buford Price
Dr. Paul Buford Price, usually known as P. Buford Price, is a professor in the Graduate School at the University of California, Berkeley and a member of the National Academy of Sciences...

 et al., sheets of clear plastic such as 1/4 mil Lexan
Lexan
Lexan is a registered trademark for SABIC Innovative Plastics' brand of polycarbonate resin thermoplastic. Polycarbonate polymer is produced by reacting Bisphenol A with carbonyl chloride, also known as phosgene. Lexan is the brand name for polycarbonate sheet and resin in a wide range of grades...

 polycarbonate can be stacked together and exposed directly to cosmic rays in space or high altitude. When returned to the laboratory, the plastic sheets are "etched" [literally, slowly dissolved] in warm caustic sodium hydroxide
Sodium hydroxide
Sodium hydroxide , also known as lye and caustic soda, is a caustic metallic base. It is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 1998 was around...

 solution, which removes the surface material at a slow, known rate. Wherever a bare cosmic ray nucleus passes through the detector, the nuclear charge causes chemical bond breaking in the plastic. The slower the particle, the more extensive is the bond-breaking along the path; and the higher the charge [the higher the Z], the more extensive is the bond-breaking along the path. The caustic sodium hydroxide dissolves at a faster rate along the path of the damage, but thereafter dissolves at the slower base-rate along the surface of the minute hole that was drilled. The net result is a conical shaped pit in the plastic; typically with two pits per sheet [one originating from each side of the plastic]. The etch pits can be measured under a high power microscope [typically 1600X oil-immersion], and the etch rate plotted as a function of the depth in the stack of plastic. At the top of the stack, the ionization damage is less due to the higher speed. As the speed decreases due to deceleration in the stack, the ionization damage increases along the path. This generates a unique curve for each atomic nucleus of Z from 1 to 92, allowing identification of both the charge and energy [speed] of the particle that traverses the stack. This technique has been used with great success for detecting not only cosmic rays, but fission product nuclei for neutron detectors.

Interaction with the Earth's atmosphere


When cosmic ray particles enter the Earth's atmosphere
Earth's atmosphere
The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 they collide with molecule
Molecule
A molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense...

s, mainly oxygen and nitrogen, to produce a cascade of lighter particles, a so-called air shower
Air shower (physics)
An air shower is an extensive cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray enters the atmosphere...

. The general idea is shown in the figure which shows a cosmic ray shower produced by a high energy proton of cosmic ray origin striking an atmospheric molecule.



This image is a simplified picture of an air shower: in reality, the number of particles created in an air shower event can reach in the billions, depending on the energy and chemical environment (i.e. atmospheric) of the primary particle. All of the produced particles stay within about one degree of the primary particle's path. Typical particles produced in such collisions are charged meson
Meson
In particle physics, mesons are subatomic particles composed of one quark and one antiquark. They are part of the hadron particle family—particles made of quarks. The other members of the hadron family are the baryons—subatomic particles composed of three quarks...

s (e.g. positive and negative pion
Pion
In particle physics, a pion is any of three subatomic particles: , and . Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force.-Basic properties:...

s and kaon
Kaon
In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...

s).

Cosmic rays are also responsible for the continuous production of a number of unstable isotopes
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron . The radionuclide, in this process, undergoes radioactive decay,...

 in the Earth’s atmosphere, such as carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, though its existence had been suggested already in 1934 by Franz Kurie. Its nucleus contains...

, via the reaction:
Cosmic rays kept the level of carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, though its existence had been suggested already in 1934 by Franz Kurie. Its nucleus contains...

 in the atmosphere roughly constant (70 tons) for at least the past 100,000 years, until the beginning of aboveground nuclear weapons testing in the early 1950s. This is an important fact used in radiocarbon dating
Radiocarbon dating
Radiocarbon dating, or carbon dating, is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to determine the age of carbonaceous materials up to about 60,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present"...

 which is used in archaeology
Archaeology
Archaeology or archeology is the science that studies human cultures through the recovery, documentation, analysis, and interpretation of material culture and environmental data, including architecture, artifacts, biofacts, and landscapes...

.

Reaction products of secondary cosmic ray, lifetime and reaction
  • Tritium
    Tritium
    Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

     (12.3 a): 14N(n, 3H)12C (Spallation
    Cosmic ray spallation
    Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from stray electrons to alpha particles....

    )
  • Beryllium-7 (53.3 d)
  • Beryllium-10
    Beryllium-10
    Beryllium-10 is a radioactive isotope of beryllium. It is formed mainly by cosmic ray spallation. Be-10 has a half-life of 1.51*106 years, and decays by beta decay to stable Boron-10 with a maximum energy of 556.2 keV....

     (1.6E6 a): 14N(n,p α)10Be (Spallation)
  • Carbon-14
    Carbon-14
    Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, though its existence had been suggested already in 1934 by Franz Kurie. Its nucleus contains...

     (5730 a): 14N(n, p)14C (Neutron activation
    Neutron activation
    Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus often decays immediately by emitting particles such as neutrons, protons, or alpha...

    )
  • Sodium-22 (2.6 a)
  • Sodium-24 (15 h)
  • Magnesium-28 (20.9 h)
  • Silicon-31 (2.6 h)
  • Silicon-32 (101 a)
  • Phosphorus-32 (14.3 d)
  • Sulfur-35 (87.5 d)
  • Sulfur-38 (2.8 h)
  • Chlorine-34 m (32 min)
  • Chlorine-36
    Chlorine-36
    Chlorine-36 is an isotope of chlorine. Chlorine has two stable isotopes and one radioactive environmental isotope: the cosmogenic isotope 36Cl. The ratio of 36Cl to stable 37Cl in the environment is ~700 × 10-15. Its half-life is 301,000 ± 4,000...

     (3E5 a)
  • Chlorine-38 (37.2 min)
  • Chlorine-39 (56 min)
  • Argon-39 (269 a)
  • Krypton-85 (10.7 a)

Research and experiments


There are a number of cosmic ray research initiatives. These include, but are not limited to:
  • Ground Experiment
    • Akeno Giant Air Shower Array
    • CHICOS
      CHICOS
      The California High School Cosmic Ray Observatory, , operated by the Kellogg Laboratory at the California Institute of Technology in Pasadena, California, USA, is one of the world's largest ongoing Cosmic Ray observatory programs...

    • High Resolution Fly's Eye Cosmic Ray Detector
      High Resolution Fly's Eye Cosmic Ray Detector
      The High Resolution Fly's Eye or HiRes detector was an ultra-high-energy cosmic ray observatory that operated in the western Utah desert from May 1997 until April 2006. HiRes utilized the atmospheric fluorescence technique that was pioneered by the Utah group first in tests at the Volcano Ranch...

    • MARIACHI
      MARIACHI
      MARIACHI, the Mixed Apparatus for Radar Investigation of Cosmic-rays of High Ionization, is an apparatus for the detection of ultra-high-energy cosmic rays via bi-static radar using VHF transmitters. MARIACHI is also the name of the research project at Brookhaven National Laboratory operating the...

    • Pierre Auger Observatory
      Pierre Auger Observatory
      The Pierre Auger Observatory is an international cosmic ray observatory designed to detect ultra-high-energy cosmic rays: single sub-atomic particles with energies beyond 1020 eV...

    • Telescope Array Project
      Telescope Array Project
      The Telescope Array project is an international collaboration involving research and educational institutions in Japan, Taiwan, China, Russia, South Korea, and the United States. The experiment is designed to observe ultra-high-energy cosmic ray air showers using a combination of ground array and...

    • Washington Large Area Time Coincidence Array
      Washington Large Area Time Coincidence Array
      The Washington Area Large-scale Time-coincidence Array is a cosmic ray physics experiment run by the University of Washington to investigate ultra high energy cosmic rays . The program uses detectors placed at Seattle-area high schools and colleges which are linked via the internet, effectively...

    • CLOUD
      CLOUD
      Cosmics Leaving Outdoor Droplets or the CLOUD is an experimental facility being set up at CERN by Jasper Kirkby to investigate the microphysics between Galactic cosmic rays and clouds under controlled conditions. The equipment is expected to become fully operational in 2011.There are two...

    • Spaceship Earth (detector)
      Spaceship Earth (detector)
      Spaceship Earth is a network of neutron monitors designed to measure the flux of cosmic rays arriving at Earth from different directions. All the 12 member neutron monitor stations are located at high latitude, which makes their detecting directions more precise, and their energy responses uniform...

    • Milagro
      Milagro (experiment)
      Milagro, , was a ground based water Čerenkov radiation telescope situated in the Jemez Mountains near Los Alamos, New Mexico. It was primarily designed to detect gamma rays but also detected large numbers of cosmic rays. It operated in the TeV region of the spectrum at an altitude of 2530 m...

    • Real-time Neutron Monitor Database (NMDB)
      Real-time Neutron Monitor Database (NMDB)
      The Real-time Neutron Monitor Database is a worldwide network of standardized neutron monitors, used to record variations of the primary cosmic rays. The measurements complement space-based cosmic ray measurements....

    • KASCADE
      KASCADE
      KASCADE is an European physics experiment started in 1996 at Forschungszentrum Karlsruhe, Germany, an extensive air shower experiment array to study the cosmic ray primary composition and the hadronic interactions in the energy range of 1016–1018 eV, measuring simultaneously...

    • GRAPES-3
      GRAPES-3
      GRAPES-3 is a project for cosmic ray study with air shower detector array and large area muon detectors at Ooty in southern India...

    • Chicago Air Shower Array
      Chicago Air Shower Array
      The Chicago Air Shower Array was a very large array of scintillation counters located in Utah, fifty miles southwest of Salt Lake City in Dugway Proving Grounds. CASA has been operating since 1992 in coincidence with a second array, the Michigan Anti , under the name CASA-MIA. The array is made...

       (CASA)
  • Satellite Experiment
    • PAMELA
    • Alpha Magnetic Spectrometer
      Alpha Magnetic Spectrometer
      The Alpha Magnetic Spectrometer, also designated AMS-02, is a particle physics experiment module that is to be mounted on the International Space Station. It is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments will help researchers study the formation...

    • ACE(Advanced Composition Explorer)
      Advanced Composition Explorer
      Advanced Composition Explorer is a space exploration mission being conducted as part of the Explorer program to study matter in situ, comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-time data from ACE is used by the Space Weather Prediction...

    • Voyager 1
      Voyager 1
      The Voyager 1 spacecraft is a 722-kilogram robotic space probe of the outer Solar System and beyond, launched September 5, 1977. It remains operational, currently pursuing its extended mission to locate and study the boundaries of the Solar System, including the Kuiper belt and beyond...

       and Voyager 2
      Voyager 2
      The Voyager 2 spacecraft is an unmanned interplanetary space probe launched on August 20, 1977. Identical in form to its sister Voyager program craft Voyager 1, Voyager 2 followed a slower trajectory that allowed it to be kept in the ecliptic so that it could be sent to Uranus and Neptune by means...

    • Cassini-Huygens
      Cassini-Huygens
      Cassini–Huygens is a joint NASA/ESA/ASI robotic spacecraft mission currently studying the planet Saturn and its moons. The spacecraft consists of two main elements: the NASA Cassini orbiter, named after the Italian-French astronomer Giovanni Domenico Cassini, and the ESA Huygens probe, named after...

    • HEAO 1, Einstein Observatory(HEAO2)
      Einstein Observatory
      Einstein Observatory was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories...

      , HEAO 3
    • Fermi Gamma-ray Space Telescope
    • Solar and Heliospheric Observatory
      Solar and Heliospheric Observatory
      The Solar and Heliospheric Observatory is a spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and began normal operations in May 1996. It is a joint project of international cooperation between the European Space Agency and NASA...

    • Interstellar Boundary Explorer
      Interstellar Boundary Explorer
      The Interstellar Boundary Explorer is a NASA satellite that will make the first map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program. IBEX was launched on a Pegasus-XL rocket on October 19, 2008, at 17:47:23 GMT...

    • LUCID (Langton Ultimate Cosmic-Ray Intensity Detector)
  • Balloon-borne Experiment

History


After the discovery of radioactivity
Radioactive decay
Radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter...

 by Henri Becquerel
Henri Becquerel
Antoine Henri Becquerel was a French physicist, Nobel laureate, and the discoverer of radioactivity, for which he won the 1903 Nobel Prize in Physics .-Early life:Becquerel was born in Paris into a family which produced four generations of scientists,...

 in 1896, it was generally believed that atmospheric electricity (ionization
Ionization
Ionization is the physical process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation ....

 of the air
Earth's atmosphere
The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

) was caused only by radiation
Radiation
In physics, radiation describes any process in which energy emitted by one body travels through a medium or through space, ultimately to be absorbed by another body...

 from radioactive elements in the ground or the radioactive gases (isotopes of radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of radium. It is one of the heaviest substances that remains a gas under normal conditions and is considered to be a health...

) they produce. Measurements of ionization rates at increasing heights above the ground during the decade from 1900 to 1910 showed a decrease that could be explained as due to absorption of the ionizing radiation by the intervening air.

In 1910 Theodor Wulf
Theodor Wulf
Theodor Wulf was a German physicist and Jesuit priest who was one of the first experimenters to detect excess atmospheric radiation....

 developed an electrometer
Electrometer
An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. There are many different types, ranging from historical hand-made mechanical instruments to high-precision electronic devices...

 (a device to measure the rate of ion production inside a hermetically sealed container) and used it to show higher levels of radiation at the top of the Eiffel Tower
Eiffel Tower
The Eiffel Tower is a 19th century iron lattice tower located on the Champ de Mars in Paris that has become both a global icon of France and one of the most recognizable structures in the world. The Eiffel Tower, which is the tallest building in Paris, is the single most visited paid monument in...

 than at its base, but his paper published in Physikalische Zeitschrift was not widely accepted. In 1912 Domenico Pacini
Domenico Pacini
Domenico Leone Pacini was an Italian physicist noted for his contributions to the discovery of cosmic ray.-Biography:...

 observed simultaneous variations of the rate of ionization over a lake, and over the sea. Pacini concluded that a certain part of the ionization must be due to sources other than the radioactivity of the Earth or the air. Then, in 1912, Victor Hess
Victor Francis Hess
Victor Francis Hess was an Austrian-American physicist, and Nobel laureate in physics, who discovered cosmic rays.-Early years:...

 built three enhanced-accuracy Wulf electrometers and carried them aloft to an altitude of 5300 meters in a free balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology and is a subset of balloon aircraft.On November 21, 1783, in Paris, France, the first manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air balloon created by the...

 flight. He found the ionization rate increased approximately fourfold over the rate at ground level. Hess also ruled out the sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the sun's visible radiation, Hess still measured rising radiation at rising altitudes. He concluded "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." In 1913–1914, Werner Kolhörster
Werner Kolhörster
Werner Heinrich Gustav Kolhörster was a German physicist and a pioneer of research into cosmic rays.Kolhörster was born in Schwiebus , Province of Brandenburg...

 confirmed Victor Hess' earlier results by measuring the increased ionization rate at an altitude of 9 km.

Hess received the Nobel Prize in Physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in chemistry, Nobel Prize in literature, Nobel Peace Prize, and...

 in 1936 for his discovery.

The term "cosmic rays" was coined by Robert Millikan
Robert Millikan
Robert A. Millikan was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. He served as president of Caltech from 1921 to 1945.-Education:Millikan went to high school in Maquoketa, Iowa...

 who proved they were extraterrestrial in origin, and not produced by atmospheric electricity as Hess had thought. Millikan believed that cosmic rays were high-energy photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

s with some secondary electron
Electron
An electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. An electron has a mass that is approximately 1836 times less than that of the proton. The intrinsic angular momentum of the electron is a half integer...

s produced by Compton scattering
Compton scattering
In physics, Compton scattering or the Compton effect is the decrease in energy of an X-ray or gamma ray photon, when it interacts with matter. Because of the change in photon energy, it is an inelastic scattering process. Inverse Compton scattering also exists, where the photon gains energy upon...

 of gamma rays. Compton himself held the (correct) belief that cosmic rays were primarily charged particles. During the decade from 1927 to 1937, a wide variety of experimental investigations demonstrated that the primary cosmic rays are mostly positively charged particles, and the secondary radiation observed at ground level is composed primarily of a "soft component" of electrons and photons and a "hard component" of penetrating particles, muon
Muon
The muon is an elementary particle similar to the electron, with negative electric charge and a spin of . Together with the electron, the tauon, and the three neutrinos, it is classified as a lepton. It is the unstable subatomic particle with the second longest mean lifetime , behind the neutron...

s. The muon was initially believed to be the unstable particle predicted by Hideki Yukawa
Hideki Yukawa
né , was a Japanese theoretical physicist and the first Japanese Nobel laureate.-Biography:Yukawa was born in Tokyo, Japan. In 1929, after receiving his degree from Kyoto Imperial University, he stayed on as a lecturer for four years. After graduation, he was interested in theoretical physics,...

 in 1935 in his theory of the nuclear force
Nuclear force
The nuclear force is the force between two or more nucleons. It is responsible for binding of protons and neutrons into atomic nuclei...

. Experiments proved that the muon decays with a mean life of 2.2 microseconds into an electron and two neutrino
Neutrino
Neutrinos are elementary particles that often travel close to the speed of light, lack an electric charge, are able to pass through ordinary matter almost undisturbed and are thus extremely difficult to detect. Neutrinos have a minuscule, but nonzero mass...

s, but that it does not interact strongly
Strong interaction
In particle physics, the strong interaction holds quarks and gluons together to form protons, neutrons and other particles. The strong interaction is one of the four fundamental interactions, along with gravitation, the electromagnetic force and the weak interaction...

 with nuclei
Atomic nucleus
The nucleus is the very dense region consisting of nucleons at the center of an atom. Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus, with a very small contribution from the orbiting electrons....

, so it could not be the Yukawa particle. The mystery was solved by the discovery in 1947 of the pion
Pion
In particle physics, a pion is any of three subatomic particles: , and . Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force.-Basic properties:...

, which is produced directly in high-energy nuclear interactions. It decays into a muon and one neutrino with a mean life of 0.0026 microseconds. The pion→muon→electron decay sequence was observed directly in a microscopic examination of particle tracks in a special kind of photographic plate called a nuclear emulsion that had been exposed to cosmic rays at a high-altitude mountain station. In 1948, observations with nuclear emulsions carried by balloons to near the top of the atmosphere by Gottlieb
Melvin B. Gottlieb
Melvin Burt Gottlieb was a high-energy physicist and director of the Princeton Plasma Physics Laboratory...

 and Van Allen
James Van Allen
James Alfred Van Allen was an American space scientist at the University of Iowa. The Van Allen radiation belts were named after him, following the 1958 satellite missions in which Van Allen had argued that a Geiger counter should be used to detect charged particles.-Honors:* TIME magazine Man of...

 showed that the primary cosmic particles are mostly proton
Proton
The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+...

s with some helium nuclei (alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as or . They have a net spin of zero, and normally a total energy of about 5 MeV...

s) and a small fraction heavier nuclei.

In 1934 Bruno Rossi
Bruno Rossi
Bruno Benedetto Rossi was a leading Italian-American experimental physicist. He made major contributions to cosmic ray and particle physics from 1930 through the 1950s, and pioneered X-ray astronomy and space plasma physics in the 1960s.-Biography:Rossi was born in Venice, Italy...

 reported an observation of near-simultaneous discharges of two Geiger counter
Geiger counter
A Geiger counter, also called a Geiger-Müller counter, is a type of particle detector that measures ionizing radiation.-Description:Geiger counters are used to detect ionizing radiation...

s widely separated in a horizontal plane during a test of equipment he was using in a measurement of the so-called east-west effect. In his report on the experiment, Rossi wrote "...it seems that once in a while the recording equipment is struck by very extensive showers of particles, which causes coincidences between the counters, even placed at large distances from one another. Unfortunately, he did not have the time to study this phenomenon more closely." In 1937 Pierre Auger
Pierre Victor Auger
Pierre Victor Auger was a French physicist, born in Paris. He worked in the fields of atomic physics, nuclear physics, and cosmic ray physics....

, unaware of Rossi's earlier report, detected the same phenomenon and investigated it in some detail. He concluded that extensive particle shower
Air shower (physics)
An air shower is an extensive cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray enters the atmosphere...

s are generated by high-energy primary cosmic-ray particles that interact with air nuclei high in the atmosphere, initiating a cascade of secondary interactions that ultimately yield a shower of electrons, photons, and muons that reach ground level.

Homi J. Bhabha
Homi J. Bhabha
Homi Jehangir Bhabha, FRS was an Indian nuclear physicist who played a major role in the development of the Indian atomic energy program and is considered to be the father of India's nuclear program. Bhabha was born into a prominent family, through which he was related to Dinshaw Maneckji Petit,...

 derived an expression for the probability of scattering positrons by electrons, a process now known as Bhabha scattering. His classic paper, jointly with Walter Heitler
Walter Heitler
Walter Heinrich Heitler was a German physicist who made contributions to quantum electrodynamics and quantum field theory...

, published in 1937 described how primary cosmic rays from space interact with the upper atmosphere to produce particles observed at the ground level. Bhabha and Heitler explained the cosmic ray shower formation by the cascade production of gamma rays and positive and negative electron pairs. In 1938 Bhabha concluded that observations of the properties of such particles would lead to the straightforward experimental verification of Albert Einstein's theory of relativity.

Measurements of the energy and arrival directions of the ultra-high-energy primary cosmic rays by the techniques of "density sampling" and "fast timing" of extensive air showers were first carried out in 1954 by members of the Rossi Cosmic Ray Group at the Massachusetts Institute of Technology
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological research...

. The experiment employed eleven scintillation detectors
Scintillator
A scintillator is material which exhibits the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e. reemit the absorbed energy in the form of a small flash of light, typically in the visible...

 arranged within a circle 460 meters in diameter on the grounds of the Agassiz Station of the Harvard College Observatory
Harvard College Observatory
The Harvard College Observatory is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, USA, and was founded in 1839...

. From that work, and from many other experiments carried out all over the world, the energy spectrum of the primary cosmic rays is now known to extend beyond 1020 eV (past the GZK cutoff
Greisen-Zatsepin-Kuzmin limit
The Greisen-Zatsepin-Kuzmin limit is a theoretical upper limit on the energy of cosmic rays from distant sources.- Computation of the GZK-limit :...

, beyond which very few cosmic rays should be observed). A huge air shower experiment called the Auger Project
Pierre Auger Observatory
The Pierre Auger Observatory is an international cosmic ray observatory designed to detect ultra-high-energy cosmic rays: single sub-atomic particles with energies beyond 1020 eV...

 is currently operated at a site on the pampa
Pampa
The Pampas are the fertile South American lowlands that include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, and Córdoba, most of Uruguay, and the southernmost end of Brazil, the Rio Grande do Sul, covering more than...

s of Argentina by an international consortium of physicists. Their aim is to explore the properties and arrival directions of the very highest energy primary cosmic rays. The results are expected to have important implications for particle physics and cosmology. In November, 2007 preliminary results were announced showing direction of origination of the 27 highest energy events were strongly correlated with the locations of active galactic nuclei
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy which has a much higher than normal luminosity over some or all of the electromagnetic spectrum . A galaxy hosting an AGN is called an active galaxy...

 [AGN], where bare protons are believed accelerated by strong magnetic fields associated with the large black hole
Black hole
In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, not even light, can escape. The black hole has a one-way surface, called an event horizon, into which objects can fall, but out of which nothing can come...

s at the AGN centers to energies of 1020 eV and higher.

Three varieties of neutrino
Neutrino
Neutrinos are elementary particles that often travel close to the speed of light, lack an electric charge, are able to pass through ordinary matter almost undisturbed and are thus extremely difficult to detect. Neutrinos have a minuscule, but nonzero mass...

 are produced when the unstable particles produced in cosmic ray showers decay. Since neutrinos interact only weakly
Weak interaction
The weak interaction is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons...

 with matter most of them simply pass through the Earth and exit the other side. They very occasionally interact, however, and these atmospheric neutrinos have been detected by several deep underground experiments. The Super-Kamiokande
Super-Kamiokande
Super-Kamiokande, or Super-K for short, is a neutrino observatory in the city of Hida, Gifu Prefecture, Japan. The observatory was designed to search for proton decay, study solar and atmospheric neutrinos, and keep watch for supernovas in the Milky Way Galaxy.The Super-K is located underground in...

 in Japan provided the first convincing evidence for neutrino oscillation
Neutrino oscillation
Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a neutrino created with a specific lepton flavor can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates...

 in which one flavour
Flavour (particle physics)
In particle physics, flavour or flavor is a quantum number of elementary particles. In quantum chromodynamics flavour is a global symmetry...

 of neutrino changes into another. The evidence was found in a difference in the ratio of electron neutrinos to muon neutrinos depending on the distance they have traveled through the air and earth.

Role in ambient radiation


Cosmic rays constitute a fraction of the annual radiation exposure of human beings on earth. For example, the average radiation exposure in Australia is 0.3 mSv
Sievert
The sievert is the SI derived unit of dose equivalent. It attempts to reflect the biological effects of radiation as opposed to the physical aspects, which are characterised by the absorbed dose, measured in gray...

 due to cosmic rays, out of a total of 2.3 mSv.

Effect on electronics


Cosmic rays have sufficient energy to alter the states of elements in electronic integrated circuit
Integrated circuit
In electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...

s, causing transient errors to occur, such as corrupted data in memory, or incorrect behavior of a CPU. This has been a problem in high-altitude electronics, such as in satellites, but as transistors become smaller it is becoming an increasing concern in ground-level equipment as well.

To alleviate this problem, Intel has proposed a cosmic ray detector which could be integrated into future high-density microprocessor
Microprocessor
A microprocessor incorporates most or all of the functions of a central processing unit on a single integrated circuit . The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal arithmetic on 4-bit words...

s, allowing the processor to repeat the last command following a cosmic ray event.

Significance to space travel



Galactic cosmic ray
Galactic cosmic ray
Galactic cosmic rays consist of those cosmic rays that enter the solar system from the outside. They are high-energy charged particles composed of protons, electrons, and fully ionized nuclei of light elements and are a strong source for cosmic ray spallation in the atmosphere of the...

s are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.

Role in lightning


Cosmic rays have been implicated in the triggering of electrical breakdown in lightning
Lightning
Lightning is an atmospheric discharge of electricity accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

. It has been proposed that essentially all lightning is triggered through a relativistic process, "runaway breakdown
Runaway breakdown
Runaway breakdown is a theory of lightning initiation proposed by Alex Gurevich in 1992.Electrons in air have a mean free path of ~1cm. Fast electrons which move at a large fraction of the speed of light have a mean free path up to 100 times longer...

", seeded by cosmic ray secondaries. Subsequent development of the lightning discharge then occurs through "conventional breakdown" mechanisms.

Role in climate change


A role of cosmic rays directly or via solar-induced modulations in recent climate change as suggested 1995 by Henrik Svensmark
Henrik Svensmark
Henrik Svensmark is a physicist at the Danish National Space Center in Copenhagen who studies the effects of cosmic rays on cloud formation.His work is connected to controversy in the area of the global warming issue...

 is still disputed. The 2007 IPCC reports mention enhanced empirical results for a stronger evidence for solar forcing of climate change, the purported attribution to cosmic rays remaining ambiguous and being less probable.

Suggested Mechanisms


Henrik Svensmark
Henrik Svensmark
Henrik Svensmark is a physicist at the Danish National Space Center in Copenhagen who studies the effects of cosmic rays on cloud formation.His work is connected to controversy in the area of the global warming issue...

 et al. have argued that solar variations modulate the cosmic ray signal seen at the earth and that this would affect cloud formation and hence climate. Cosmic rays have been experimentally determined to be able to produce ultra-small aerosol particles, orders of magnitude smaller than cloud condensation nuclei
Cloud condensation nuclei
Cloud condensation nuclei or CCNs are small particles about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny solid or liquid particles called CCNs...

 (CCN).

According to a report about an ongoing CERN CLOUD
CLOUD
Cosmics Leaving Outdoor Droplets or the CLOUD is an experimental facility being set up at CERN by Jasper Kirkby to investigate the microphysics between Galactic cosmic rays and clouds under controlled conditions. The equipment is expected to become fully operational in 2011.There are two...

 research project to detect any Cosmic ray forcing is challenging since on wide spread time scales changes in the Sun’s magnetic activity, Earth’s magnetic field, and the galactic environment have to be taken into account. Empirically, increased galactic cosmic ray (GCR) flux seem to be associated with a cooler climate, a southerly shift of the ITCZ (Inter Tropical Convergence Zone) and a weakening of monsoon rainfalls and vice versa. Claims have been made of identification of GCR climate signals in atmospheric parameters such as high latitude precipitation (Todd & Kniveton), and Svensmark's annual cloud cover variations, which were said to be correlated to GCR variation. Various proposals have been made for the mechanism by which cosmic rays might affect clouds, including ion mediated nucleation, and indirect effects on current flow density in the global electric circuit (see Tinsley 2000, and F. Yu 1999). Other studies refer to the formation of relatively highly charged aerosols and cloud droplets at cloud boundaries, with an indirect effect on ice particle formation and altering aerosol interaction with cloud droplets.
Kirkby (2009) reviews developments and describes further cloud nucleation mechanisms which appear energetically favorable and depend on GCRs.,

Geochemical and astrophysical evidence



Nir Shaviv
Nir Shaviv
Nir Joseph Shaviv is an Israeli/American physics professor, carrying out research in the fields of astrophysics and climate science. He is currently an associate professor at the Racah Institute of Physics of the Hebrew University of Jerusalem.He is most well-known for his solar and cosmic rays...

 has argued that climate signals on geological time scales are attributable to changing positions of the galactic spiral arms of the Milky Way, and that cosmic ray flux variability is the dominant climate driver over these time periods. Nir Shaviv and Jan Veizer
Jan Veizer
Ján Veizer is the Distinguished University Professor of Earth Sciences at the University of Ottawa and Institute for Geology, Mineralogy und Geophysis, of Bochum Ruhr University, he held the NSERC/Noranda/CIFAR Industrial Chair in Earth System Isotope and Environmental Geochemistry until 2004...

 in 2003 argue, that in contrast to a carbon based scenario, the model and proxy based estimates of atmospheric CO2 levels especially for the early Phanerozoic
Phanerozoic
The Phanerozoic eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 545 million years and goes back to the time when diverse hard-shelled animals first appeared...

 (see diagrams) do not show correlation with the paleoclimate picture that emerged from geological criteria, while cosmic rays flux would do.

The 2007 IPCC reports however strongly attribute a major role of anthropogenic carbon dioxide in the ongoing global warming, but as "different climate changes in the past had different causes" a driving role of Carbon dioxide in the geological past is neither focus of the IPCC nor purported. Similarly, according a BBC report a 2008 Lancaster University
Lancaster University
Lancaster University, officially The University of Lancaster, is a British university in Lancaster, Lancashire, England. Lancaster is the 7th highest ranking research institution in the United Kingdom according to the last Research Assessment Exercise. The University has an annual income of £149...

 study produced "further compelling evidence showing that modern-day climate change is not caused by changes in the Sun's activity".

A comprehensive study of different research institutes was published 2007 by Scherer et al. in Space Science Reviews 2007. The study combines geochemical evidence both on temperature, cosmic rays influence and as well astrophysical deliberations suggesting a major role in climate variability over different geological time scales. Proxy data of CRF influence comprise among others isotopic evidence in sediments on earth and as well changes in (iron) meteorites.

Lacking evidence of an accepted mechanism relating cosmic ray and climate e.g. via cloud cover variation and the challenges to obtain correct historical data on cosmic ray flux at various ranges of energies still lead to controversies

See-also Global warming#Solar variation.

See also

  • Environmental radioactivity
    Environmental radioactivity
    Environmental radioactivity is the study of radioactive materials in the human environment. While some radioisotopes are only found on Earth as a result of human activity, such as Strontium-90 and Technetium-99 , and some isotopes like Potassium-40 are only present due to natural processes, a...

  • Cosmic ray spallation
    Cosmic ray spallation
    Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from stray electrons to alpha particles....

  • Gilbert Jerome Perlow
    Gilbert Jerome Perlow
    Gilbert "Gil" Jerome Perlow , was an American physicist famous for his work related to the Mossbauer effect, and an editor of the Journal of Applied Physics and Applied Physics Letters.- Life :...

  • Ultra-high-energy cosmic ray
    Ultra-high-energy cosmic ray
    In high-energy physics, an ultra-high-energy cosmic ray or extreme-energy cosmic ray is a cosmic ray which appears to have extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays...

  • Galactic cosmic ray
    Galactic cosmic ray
    Galactic cosmic rays consist of those cosmic rays that enter the solar system from the outside. They are high-energy charged particles composed of protons, electrons, and fully ionized nuclei of light elements and are a strong source for cosmic ray spallation in the atmosphere of the...

  • Extragalactic cosmic ray
    Extragalactic cosmic ray
    Extragalactic cosmic rays are very-high-energy particles that flow into our solar system from beyond our galaxy. The energies these particles possess are in excess of 1015 eV.- Origin :...

  • Stellar radiation
  • Solar energetic particle
  • Track Imaging Cherenkov Experiment
    Track Imaging Cherenkov Experiment
    The Track Imaging Cherenkov Experiment is a ground-based cosmic ray telescope located at Argonne National Laboratory near Chicago, IL. The telescope, which contains a Fresnel lens, eight spherical mirrors, and a camera with 16 multianode photomultiplier tubes, uses the atmospheric Cherenkov...


External links