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🔎 Cosmic Ray – Definition and Explanations


the cosmic radiation is the flux of atomic nuclei and high-energy (i.e. relativistic) particles circulating in the interstellar vacuum. Today we also refer to the ” cosmic rays » under the name ofastroparticles.

Some of these particles, from solar, galactic or extragalactic sources can cross us, interfere with DNA, cross the rock (Rock, from the popular Latin rocca, means any material that makes up the bark…) and buildings and deeply penetrate the planetary soil and subsoil.

The study of radiation (Radiation, synonymous with radiation in physics, designates the process of emission or…) cosmic began at the beginning of the XXe century with the work of Victor Hess.

Part of the bass cosmic rays energy (In common sense, energy designates everything that allows you to do work, make energy, etc.) (relative to the rest of the cosmic rays: of the order of MeV), trapped by the earth’s magnetic field (The Earth has a magnetic field produced by the movements of its outer core –…)participates in the formation of the Van Allen belts.


It begins in 1900, when Charles Thomson Rees Wilson (Charles Thomson Rees Wilson (1869 in Glencorse, Scotland – 1959 in Carlops, Scotland)…) discovers that the atmosphere is continuously ionized. He then thinks that it is due to the natural radiation of the Earth (Earth is the third planet in the Solar System in order of distance…). His research on theatmospheric electricity (To delete)I’ionization (Ionization is the action of removing or adding charges to an atom or a…) and the condensation (Condensation is the name given to the physical phenomenon of change of state of matter which…) led him to design the first cloud chamber (A cloud chamber is a particle detector in which the ionization produced by the…).

But quickly, the scientists of the time are intrigued by the excess of ions compared to the amount (The quantity is a generic term of metrology (account, amount); a scalar,…) normally due to natural ground radiation. In 1912 the physicist (A physicist is a scientist who studies the field of physics, i.e….) Austrian Victor Franz Hess (Victor Franz Hess (June 24, 1883 – December 17, 1964) was a…) measures the ionization rate as a function of altitude with a electrometer (An electrometer (also called electroscope) is a scientific measuring device allowing the…) at sheet (The leaf is the organ specialized in photosynthesis in plants…) of gold embedded in a balloon. The ionization decreases to 700m, then grows beyond. There are few differences between the day (The day or the day is the interval which separates the sunrise from the sunset; it is the…) and the night. Hess concludes from this the cosmic origin (that is to say outside the solar system) of this radiation. These results are confirmed by Robert Millikan who works using sounding balloons.

Hess also thinks that these rays are electrically neutral. This assertion was denied as early as 1928 when it was shown that most of the radiation reaching the surface (A surface generally refers to the superficial layer of an object. The term a…) Earth is made up of charged particles. Millikan then assumes that the latter result from theinteraction (An interaction is an exchange of information, affects or energy between two agents within…) between the neutral rays of space (gamma radiation) and the molecules of theatmosphere (The word atmosphere can have several meanings:). Arthur Compton (Arthur Holly Compton (September 10, 1892 in Wooster, Ohio, United States -…) demonstrates that the radiation is in fact variable (In mathematics and logic, a variable is represented by a symbol. It…) following the latitude (Latitude is an angular value, expression of the north-south positioning of a point on Earth…) where it is measured (lower at the equator than at the poles) due to the influence of the magnetic field (In physics, the magnetic field (or magnetic induction, or flux density…) terrestrial, thereby proving that they are charged particles.

Diagram of an atmospheric cascade produced by a proton (The proton is a subatomic particle carrying an elementary electric charge…)

In 1938 theastronomer (An astronomer is a scientist who specializes in the study of astronomy.) French Pierre Auger (Pierre Victor Auger (May 14, 1899 – December 25, 1993) was a French physicist born in Paris,…) discovers that these particles form atmospheric showers. These particles are called “secondary”, as opposed to the “primary” particles constituting the flow (The word flux (from the Latin fluxus, flow) generally designates a set of elements…) before interaction with the atmosphere.


Spectrum of primary cosmic radiation (flow of astroparticles at the top of the Earth’s atmosphere); per unit area (m²) per unit of time (Time is a concept developed by human beings to apprehend the…) (sec.) per unit ofsolid angle (In mathematics, geometry, and physics, a solid angle is the three-dimensional analog of…) (steradian sr) and per incident particle energy interval of 1 gigaelectron-volt

The low energies (yellow zone) come mainly from the Sun (The Sun (Sol in Latin, Helios or Ήλιος in Greek) is the star…)the intermediate energies (blue) of galactic cosmic rays, and the highest energies (purple) are extragalactic

The radiation spectrum is the function relating the incident flux of particles with their energy.
The figures opposite have a logarithmic scale (A logarithmic scale is a graduation system on a half-line[Ox))[Ox)) to integrate the very large amplitude (In this simple wave equation:) values ​​of the energies and fluxes measured.
This spectrum is given here for the primary radiationi.e. before the interaction of this radiation with the atmosphere.

This spectrum is clearly “non-thermal”that is to say, it does not result from the emission of a body to a temperature (Temperature is a physical quantity measured using a thermometer and…) data (In information technologies, a datum is an elementary description,…) (black body spectrum). The slope of the line shows that the flux decreases rapidly according to a law of Powerful (The word power is used in several fields with a particular meaning:). L’exponent (Expositor can mean:) of the power law is called the spectral index. Its overall value is 2.8.

There are, however, two slope breaks remarkable, although quite discreet to the naked eye.
– The first, at 5.1015 eV is nicknamed the “ knee (flux: 1 particle/m2/year). Spectral Index increased from approximately 2.7 to 3.0.
– The second (Second is the feminine of the adjective second, which comes immediately after the first or which…)located at 4.1019 eV is nicknamed the “ ankle (flux: 1 particle/km2/year). the spectral index goes to 3.3.