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.
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).
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
Why Cosmic Rays are important?
Cosmic rays are like tiny space travelers that zoom through the universe. When they crash into the air around Earth, they create brand-new stuff, like special versions of elements. One of these, called carbon-14, helps scientists figure out how old ancient things are.
These cosmic rays also team up with oxygen way up high in the sky to make a protective layer called ozone. This ozone acts like a shield, keeping us safe from the sun’s powerful rays.
Imagine cosmic rays as messengers from distant parts of the universe. By studying them, scientists uncover secrets about what our universe is made of and how it changes over time.
But these rays do even more! They’re like a vital part of nature’s balancing act, crucial for life on our planet.
Cosmic rays are important for a number of reasons, including:
Let’s look at some cool ways scientists use cosmic rays:
- They help to create new elements. Cosmic rays collide with atoms in the Earth’s atmosphere, creating new isotopes and even new elements. For example, the element carbon-14, which is used in radiocarbon dating, is created by cosmic rays.
- They help to produce ozone. Cosmic rays interact with oxygen molecules in the upper atmosphere to produce ozone. Ozone is important because it protects us from harmful ultraviolet radiation from the sun.
- They provide us with information about the universe. Cosmic rays come from all over the universe, and by studying them, we can learn more about the composition and evolution of the cosmos.
In addition to these specific benefits, cosmic rays play an important role in the overall health of the planet. They are part of the balance of nature, and their presence is essential for life on Earth.
Here are some specific examples of how cosmic rays are used in science and technology:
- Radiocarbon dating: Cosmic rays create carbon-14 in the atmosphere, which is absorbed by plants and then animals when they eat plants. Carbon-14 decays at a known rate, so by measuring the amount of carbon-14 in organic matter, scientists can determine its age. This technique is used to date archaeological artifacts, geological samples, and even human remains.
- Particle physics: Cosmic rays are a source of high-energy particles, which can be used to study the fundamental nature of matter. Physicists use particle accelerators to collide cosmic rays with other particles, and by studying the resulting collisions, they can learn more about the forces and particles that make up the universe.
- Medical imaging: Cosmic rays can be used to produce medical isotopes, which are used in imaging techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). These imaging techniques can be used to diagnose diseases and monitor the effectiveness of treatments.
Cosmic rays are a fascinating and important part of our universe. By studying them, we can learn more about the world around us and develop new technologies that benefit society.
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 ray, GCR ) 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.
- 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.
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.
What are the dangers with cosmic rays?
Cosmic rays are high-energy particles that come from outside our solar system. They can pose a number of dangers to astronauts and to electronic systems in space.
Dangers to astronauts
Cosmic rays can damage astronauts’ DNA, which can lead to cancer and other health problems. The risk of these problems increases with the amount of time spent in space.
Dangers to electronic systems
Cosmic rays can also damage electronic systems, such as those used in satellites and spacecraft. This can lead to malfunctions and even system failures.
Cosmic rays can also produce secondary radiation, which is even more dangerous than cosmic rays themselves. Secondary radiation can damage cells and cause health problems.
NASA has developed a number of mitigation measures to protect astronauts from cosmic radiation. These include:
- Shielding: Spacecraft are shielded with thick layers of material to block cosmic rays.
- Limiting exposure time: Astronauts are limited in the amount of time they spend outside of spacecraft, where they are more exposed to cosmic radiation.
- Monitoring: Astronauts are monitored for signs of radiation exposure and health problems.
Cosmic rays are a serious danger to astronauts and electronic systems in space. However, NASA has developed a number of mitigation measures to protect astronauts and spacecraft.
Cosmic rays are also a danger to commercial air travel. At high altitudes, passengers and crew are exposed to higher levels of cosmic radiation. This exposure can increase the risk of cancer and other health problems.
Airlines have taken steps to mitigate the risk of cosmic radiation exposure, such as:
- Limiting flight times: Airlines try to limit the amount of time that passengers and crew spend at high altitudes.
- Changing flight routes: Airlines sometimes change flight routes to avoid areas of high cosmic radiation.
- Shielding: Aircraft are shielded with materials to block cosmic rays.
However, the risk of cosmic radiation exposure on commercial air travel is still relatively low. The average passenger is exposed to about 0.33 millisieverts (mSv) of cosmic radiation per year. This is equivalent to the amount of radiation from about three chest X-rays.
Photo credit: NASA, Public domain, via Wikimedia Commons
NGC 6357, 5,500 light years away, has young, hot stars charging up the gas. The image combines data from Chandra (purple), Spitzer (orange), and SuperCosmos (blue).
It’s a cluster of star groups, some big and bright. Chandra and ROSAT telescopes reveal many young stars and hot gas, along with bubbles from powerful rays.
Scientists call NGC 6357 an “HII” region, formed by hot stars charging up the gas. They use Chandra to study it, as it detects bright X-rays from young stars and can see through gas and dust clouds, revealing details of star birth.