Cosmic radiation. Cosmic rays are subatomic particles that come from outer space and that have a high energy due to their high speed, close to the speed of light . They were discovered when it could be verified that the electrical conductivity of the Earth’s atmosphere was due to ionization caused by high-energy radiation.
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- 1 Origins
- 2 Cosmic rays in the atmosphere
- 3 Protection of the magnetosphere
- 4 Sources
The origin of cosmic rays is still unclear. The Sun is known to emit low-energy cosmic rays in periods when large solar flares occur, but these stellar phenomena are rare; therefore, they do not explain the origin of cosmic rays, nor do they explain the eruptions of other Sun-like stars. Large supernova explosions are at least responsible for the initial acceleration of much of the cosmic rays, since that the remains of these explosions are powerful radio sources, which imply the presence of high-energy electrons.
In 2007 , a group of Argentine scientists from the Pierre Auger Observatory made a spectacular discovery that launched a new branch of astronomy. This group found evidence that most of the cosmic ray particles come from a nearby constellation, Centaurus.
This constellation in such a case contains an active nucleus galaxy and its active nucleus is due to the presence of a black hole (probably supermassive), as matter falls into the ergosphere of the black hole and rotates rapidly, part of such matter escapes to enormous speeds, centrifugally, in the form of protons and neutrons; Upon reaching Earth (or other planets with sufficiently dense atmospheres) only protons arrive that fall in cascades of cosmic rays after colliding with the upper atmospheric layers. The discovery observed in Centaurus seems to be extrapolated to all galaxies with nuclei activated by black holes.
It is also believed that additional acceleration occurs in interstellar space as a result of shock waves from supernovae propagating there. There is no direct evidence that supernovae contribute significantly to cosmic rays. However, it is suggested that X-ray binary stars may be cosmic ray sources. In those systems, a normal star gives up mass to its companion, a neutron star, or a black hole .
Radio astronomical 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.
Cosmic rays in the atmosphere
The cosmic rays reaching the atmosphere in its upper layer are mainly (98%) protons and high-energy alpha particles. The rest are electrons and ionized heavy particles. These are called primary particles.
These charged particles interact with the atmosphere and the Earth’s magnetic field, transforming into secondary particles (they are the product of the interaction of the primary particles with the atmosphere) and distributing so that the highest intensity of the particles reaching the ground will be at the poles (due to the magnetic field).
Therefore, the component of particles that reach the ground varies according to altitude (the higher the altitude, the less atmosphere to interact with), the latitude (the higher the latitude, the greater the number of particles deflected by the magnetic field ) and they vary somewhat with the solar cycle (11 years).
At sea level, and for a latitude of about 45ºN, the main components are muons (72%), photons (15%) and neutrons (9%). The doses received due to cosmic rays are between 300 μSv and 2000 μSv per year. Averaged by population, occupation data and other factors, an average value of 380 μSv / year is found.
Protection of the magnetosphere
Like electrically charged particles, the ions that make up cosmic radiation are oriented or deflected by magnetic fields, such as a compass needle. Now, the Earth can be considered as a great magnet surrounded by a magnetic field whose lines of force “enter” through the North Pole “to leave” the South Pole: it is what is called the magnetosphere.
If the cosmic particles have an energy higher than a certain maximum limit, called magnetic cut energy, they cross the magnetosphere and reach the upper layers of the atmosphere. But if their energy is not enough, then they tend to follow the lines of force of the magnetic field, with more “ease” they already have less energy, and thus reach the poles. This is the reason why the areas located near the poles suffer a higher irradiation than that of Ecuador, better protected by the Earth’s magnetic field.