Cosmic Rays | Let’s talk about science

Cosmic rays

What are Cosmic Rays?

Cosmic rays are subatomic particles that come from outer space and that have high energy due to their high speed. They were discovered when it was found that the electrical conductivity of the Earth’s atmosphere was due to ionization caused by high-energy radiation.

Their energy is typically 1 GeV (the energy that an electron would have accelerated by an electrical voltage of one billion Volts), but it sometimes goes up to 10 to the power of 11 GeV. These particles could have been accelerated during explosions of Supernovae. The Sun also emits high energy particles, but generally much lower than the GeV.

Victor Franz Hess (an American physicist of Austrian origin) demonstrated in 1911 that atmospheric ionization increases with altitude, and concluded that the radiation must come from outer space.

The discovery that the intensity of radiation depends on altitude tells us that the particles that make up the radiation are electrically charged and that they are deflected by the Earth’s magnetic field.

They are a very fast charged particle from the interstellar medium. These particles are mostly protons (85%), helium nuclei (14%), electrons (1%) and other atomic nuclei.

The highest energy measured for a single cosmic ray particle is comparable to the kinetic energy of a baseball moving at about 100 miles per hour, so it is more than a hundred million times greater than the energy of protons accelerated in the CERN LHC.

Read also: Zetta Particles – Definition and Explanations of Ultra high energy cosmic rays

We are constantly exposed to ionizing radiation, whether natural or artificial, visible or invisible

Sunlight is visible natural radiation, which is accompanied by invisible radiation (ultraviolet and infrared).

Among the natural radiation, some come from space and are known as cosmic radiation (or rays). Others come from ambient radioactivity (coming from rocks or radon gas).

These pages provide information on cosmic rays, which represent about 11% of sources of ionizing radiation (this percentage depends in particular on where you are).

Nucleosynthesis periodic table
Periodic table of the elements drawn according to the origin of the latter. The work is inspired by the site Jennifer Johnson, Ohio State University.
Big Bang fusion = elements from the Big Bang.
Exploding massive stars = items created when massive stars die.
Cosmic rays fission = elements created by the interaction of matter with cosmic rays
Dying low-mass stars = elements from smaller stars.
Merging neutron stars: Elements resulting from the collision between neutron stars.
Exploding white dwarfs: Elements resulting from the explosion of white dwarfs. Cmglee, CC BY-SA 3.0, via Wikimedia Commons

The origin of cosmic rays is still unclear

The Sun is known to emit low-energy cosmic rays during periods of large solar flares, but these stellar phenomena are not frequent, so they do not explain the origin of cosmic rays. Neither do the eruptions of other stars similar to the Sun.

Large supernova explosions are at least responsible for the initial acceleration of much of the cosmic rays, as the remnants of these explosions are powerful radio sources, implying the presence of high-energy electrons.

Additional acceleration is also believed to occur in interstellar space as a result of shock waves from supernovae that propagate there. There is no direct evidence that supernovae contribute significantly to cosmic rays. However, it is suggested that X – ray binary stars may be sources of cosmic rays. In these systems, a normal star gives up mass to its companion, a neutron star or black hole .

Radio astronomy studies of other galaxies show that they also contain high-energy electrons. The centers of some galaxies emit radio waves with much greater intensity than the Milky Way, indicating that they contain sources of high-energy particles.

The physical mechanism that produces these particles is not known.

Sources of ionizing radiation in interplanetary space. NASA/JPL-Caltech/SwRI, Public domain, via Wikimedia Commons

The origin of cosmic rays

The origin of cosmic rays is not fully understood.

The sun is clearly an important source of cosmic rays but these have a fairly low energy (a few tens of GeV). The sun is a sphere of gas, mostly hydrogen. Given the temperature of the surface of the sun (~ 5000 C) hydrogen is ionized: protons. Under the effect of the magnetic fields prevailing on the surface of the sun, these protons are accelerated, and give rise to the “solar wind” and create the aurora borealis on the Earth.

Characteristics and properties

Cosmic rays, extraterrestrial particles that are:

1. Either electrically charged as:
  • the nuclei of hydrogen atoms (protons), helium (alphas), carbon, etc.
  • electrons and “muons” (very similar to electrons but 200 times more massive)
2. Either electrically neutral as:
  • neutrons (brother of neutral of the proton)
  • photons (the “grains” of light).

Fermi Proves Supernova Remnants Produce Cosmic Rays

Study using observations from NASA’s Fermi Gamma-ray Space Telescope reveals the first clear-cut evidence that the expanding debris of exploded stars produces some of the fastest-moving matter in the universe. This discovery is a major step toward meeting one of Fermi’s primary mission goals.

Classification and designations by origin

Depending on the origin, the cosmic rays are divided into solar radiation (solar cosmic ray , SCR ), galactic (galactic cosmic rayGCR ) and extragalactic radiation.

1. Solar wind
Particle flux densities around 10 7 cm −2 s −1 , low energies, mainly protons and alpha particles. Particle density around 5 cm −3 . Cause of the Aurora Borealis.
2. Solar flares, Coronal mass ejection
Characteristics: temporal increase in particle flux within a few hours and days to 10 8 to 10 10 cm −2 s −1 , energies around 10 MeV, particle density up to 50 cm −3.
3. Van Allen radiation belt
Is sometimes counted among cosmic rays.
4. Galactic or Milky Way Cosmic Rays (GCR)
Low particle flux densities, very high energies (1 GeV and higher), proportion of heavy ions up to iron. With increasing energy, the deflection by magnetic fields decreases and the anisotropy of the radiation increases.

Anisotropy is the property of variation in physical properties when measured from different directions. It is the opposite property to isotropy .

5. Anomalous cosmic rays (ACR)

Most probably arises from the interaction of the solar wind with the local interstellar matter (Interstellar medium) in the outer region of the heliosphere , between termination shock and heliopause. Characteristics: lower energy than GCR, fewer hydrogen and carbon ions than hydrogen and carbon in the LISM.

6. Extragalactic cosmic rays

Maximum energies up to some 10 20  eV. The flux densities are below 10 −20 particles per second and square meter. Like the galactic cosmic rays, the extragalactic consists of protons and heavier ions.

Discovery and History

It is said that Charles de Coulomb had already suspected the existence of charged radiation at the base of the slow discharge of a charged sphere. In a more concrete way it will be necessary to wait for the beginning of the 20th century so that the cosmic rays are highlighted.

1910: Father Wulf studies while climbing the Eiffel Tower and demonstrates that the ionizing radiation observed is not only due to natural radioactivity, but that part of it comes “from above”

1912: Victor Hess, by loading a device sensitive to rays (see photos opposite) in a balloon, concludes that there is an unknown radiation coming not from the earth, but from space: cosmic rays. Their study led to the birth of “particle physics”.

1925: Robert Millikan thinks that the charged radiation highlighted by Hess is made up of gamma rays: from this is born the expression “cosmic rays”.

1930: Arthur Compton, by sending sixty researchers to carry out measurement campaigns around the world, proves that cosmic rays are made up of charged particles, sensitive to the effects of latitude.

1938: Pierre Auger sets up on mountain tops with particle detectors.

How to detect them?

There are 2 ways to detect them: direct and Indirect detections.

1. Direct detection

Direct detection is possible by all kinds of particle detectors on the ISS, on satellites, or in high-altitude balloons. However, there are weight and size restrictions that limit detector options.

An example of the direct detection technique is a nuclear track -based method developed by Robert Fleischer, P. Buford Price , and Robert M. Walker for use in high-altitude balloons. In this method, sheets of clear plastic, such as 0.25mm  Lexan polycarbonate, are stacked and directly exposed to cosmic rays in space or at high altitudes. Nuclear charge causes chemical bond breaking or ionizationin the plastic. At the top of the plastic pile, ionization is less, due to the high speed of cosmic rays. As the speed of the cosmic rays decreases due to the slowdown in the stack, the ionization increases along the way. The resulting plastic sheets are “etched” or slowly dissolved in a hot caustic solution of sodium hydroxide, which removes material from the surface at a slow and known rate. Caustic sodium hydroxide dissolves plastic at a faster rate along the path of ionized plastic. The net result is a conical pitting in the plastic. Pitting is measured with a high-powered microscope (typically 1600× oil immersion), and the rate of etching is plotted as a function of depth into the stacked plastic.

This technique produces a unique curve for each atomic nucleus from 1 to 92, making it possible to identify both the charge and the energy of the cosmic ray passing through the plastic stack. The more extensive the ionization along the path, the greater the charge. In addition to its uses for cosmic ray detection, the technique is also used to detect nuclei created as nuclear fission products .

2. Indirect detection

There are several terrestrial methods of cosmic ray detection currently in use, which can be divided into two main categories: the detection of secondary particles that form extensive air showers (EAS) by various types of particle detectors, and the detection of electromagnetic radiation; emitted by EAS into the atmosphere.

The extensive air shower arrays formed by particle detectors measure the charged particles that pass through them. EAS arrays can observe a wide area of ​​the sky and can be active more than 90% of the time. However, they are less capable of separating the background effects of cosmic rays than air Cherenkov telescopes . Most of the latest generation EAS sets use plastic scintillators. Water (liquid or frozen) is also used as a detection medium through which the particles pass and produce Cherenkov radiation to make them detectable. For this reason, several matrices use water/ice-Cherenkov detectors as an alternative to or in addition to scintillators. By combining several detectors, some EAS arrays have the ability to distinguish muons from lighter secondary particles (photons, electrons, positrons). The fraction of muons among secondary particles is a traditional way of estimating the mass composition of primary cosmic rays.

Sources: PinterPandai, Space, Britannica

Photo credit: NASA (Public Domain) via Wikimedia Commons

Phto description: Cosmic ‘Winter’ Wonderland

Although there are no seasons in space, this cosmic vista invokes thoughts of a frosty winter landscape. It is, in fact, a region called NGC 6357 where radiation from hot, young stars is energizing the cooler gas in the cloud that surrounds them.This composite image contains X-ray data from NASA’s Chandra X-ray Observatory and the ROSAT telescope (purple), infrared data from NASA’s Spitzer Space Telescope (orange), and optical data from the SuperCosmos Sky Survey (blue) made by the United Kingdom Infrared Telescope.

Located in our galaxy about 5,500 light years from Earth, NGC 6357 is actually a “cluster of clusters,” containing at least three clusters of young stars, including many hot, massive, luminous stars. The X-rays from Chandra and ROSAT reveal hundreds of point sources, which are the young stars in NGC 6357, as well as diffuse X-ray emission from hot gas. There are bubbles, or cavities, that have been created by radiation and material blowing away from the surfaces of massive stars, plus supernova explosions.

Astronomers call NGC 6357 and other objects like it “HII” (pronounced “H-two”) regions. An HII region is created when the radiation from hot, young stars strips away the electrons from neutral hydrogen atoms in the surrounding gas to form clouds of ionized hydrogen, which is denoted scientifically as “HII”.

Researchers use Chandra to study NGC 6357 and similar objects because young stars are bright in X-rays. Also, X-rays can penetrate the shrouds of gas and dust surrounding these infant stars, allowing astronomers to see details of star birth that would be otherwise missed.

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