Van Allen's Radiation Belt

The Earth's radiation belt (RPG), or Van Allen's belt, is the region of the nearest cosmic space near our planet, which has the form of a ring in which there are giant streams of electrons and protons. The earth retains them by means of a dipole magnetic field.

Opening

RPG was discovered in 1957-58. Scientists from the United States and the USSR. "Explorer-1" (pictured below), the first US space satellite, launched in 1958, provided very important data. Due to the onboard experiment conducted by the Americans on the Earth's surface (at an altitude of about 1000 km), a radiation belt (internal) was found. Later, at an altitude of about 20,000 km, a second such zone was discovered. There is no clear boundary between the inner and outer belts - the first gradually passes into the second. These two zones of radioactivity differ in the degree of charge of particles and their composition.

These areas became known as Van Allen's belts. James Van Allen is a physicist whose experiment helped to discover them. Scientists have found out that these belts consist of a solar wind and charged particles of cosmic rays, which are attracted to the Earth by its magnetic field. Each of them forms a torus around our planet (a figure that resembles a donut in shape).

In space since that time, many experiments have been carried out. They allowed us to investigate the main features and properties of the RPG. Not only our planet has radiation belts. They are also found in other celestial bodies, which have an atmosphere and a magnetic field. Van Allen's radiation belt was discovered, thanks to the interplanetary ships of the USA from Mars. In addition, the Americans found it in Saturn and Jupiter.

Dipole magnetic field

Our planet has not only Van Allen's belt, but also a dipole magnetic field. It is a set of magnetic shells nested inside each other. The structure of this field resembles the head of cabbage or an onion. A magnetic shell can be imagined as a woven surface woven from power magnetic lines. The closer the shell is to the center of the dipole, the greater the intensity of the magnetic field. In addition, the momentum that is required for a charged particle to penetrate it from the outside also increases.

Thus, the Nth shell has a particle momentum P _n . In the case when the initial momentum of the particle does not exceed P _n , it reflects the magnetic field. The particle then returns to outer space. However, it also happens that it is on the N-th shell. In this case, she is no longer able to leave it. The trapped particle will be trapped until it dissipates or, after colliding with the residual atmosphere, does not lose energy.

In the magnetic field of our planet, the same shell is at a different distance from the earth's surface at different longitudes. This is due to the mismatch of the axis of the magnetic field with the axis of rotation of the planet. This effect is most noticeable over the Brazilian magnetic anomaly. In this area, the magnetic lines of force are lowered, and the trapped particles moving along them can be below 100 km altitude, which means that they die in the earth's atmosphere.

The composition of the RPG

Inside the radiation belt, the distribution of protons and electrons is not the same. The first are in its internal part, and the second - in the outer. Therefore, at an early stage of the research, scientists believed that there are external (electronic) and internal (proton) radiation belts of the Earth. Currently, this opinion is irrelevant.

The most significant mechanism of generation of Van Allen's filling belts is the decay of albedo neutrons. It should be noted that neutrons are created when the atmosphere interacts with cosmic radiation. The flow of these particles moving in the direction from our planet (albedo neutrons) passes through the Earth's magnetic field unimpeded. However, they are unstable and easily decay into electrons, protons, and electron antineutrinos. Radioactive albedo nuclei, which have a high energy, decay inside the capture zone. This is how Van Allen's belt is replenished with positrons and electrons.

RPG and magnetic storms

When strong magnetic storms begin, these particles are not just accelerated, they leave the Van Allen radioactive belt, getting enough sleep out of it. The point is that if the configuration of the magnetic field changes, the mirror points can be immersed in the atmosphere. In this case, the particles, losing energy (ionization losses, scattering) change the pitch angles, and then die, reaching the upper layers of the magnetosphere.

RPG and aurora borealis

Van Allen's radiation belt is surrounded by a plasma layer, which is captured streams of protons (ions) and electrons. One of the reasons for such a phenomenon as the northern (polar) radiance is that the particles emerge from the plasma layer, and also partially from the outer RPG. The Northern Lights is the radiation of atmospheric atoms, which are excited due to a collision with particles that have spilled out from the belt.

The RPG study

Almost all the basic results of studies of such formations as radiation belts were obtained approximately in the 1960s-1970s. Recent observations using orbital stations, interplanetary ships and the latest scientific equipment allowed scientists to extract very important new information. Belts of Van Allen around the Earth continue to be studied in our time. In brief, we will talk about the most important achievements in this field.

The data received from "Salyut-6"

Researchers from MEPhI in the early 80s of the last century investigated the flow of electrons with a high level of energy in the immediate vicinity of our planet. To do this, they used the equipment that was on the Salyut-6 orbital station. It allowed scientists to efficiently isolate the fluxes of positrons and electrons whose energy exceeds 40 MeV. The station's orbit (inclination 52 °, altitude about 350-400 km) passed mainly below the radiation belt of our planet. However, it still touched its internal part from the Brazilian magnetic anomaly. At the intersection of this region, stationary flows consisting of high-energy electrons were found. In the RPG, before this experiment, only electrons were recorded whose energy did not exceed 5 MeV.

The data of artificial satellites of the "Meteor-3"

Researchers from MEPhI conducted further measurements on artificial satellites of our planet "Meteor-3" series, in which the height of circular orbits was 800 and 1200 km. This time the device has penetrated the RPG very deeply. He confirmed the results obtained earlier at the Salyut-6 station. Then the researchers obtained another important result, using magnetic spectrometers installed at Mir and Salyut-7 stations. It was proved that the previously discovered stable belt consists exclusively of electrons (without positrons), whose energy is very high (up to 200 MeV).

The discovery of the stationary belt of CNO nuclei

A group of researchers from the Institute of Nuclear Physics of the Moscow State University in the late 1980s and early 90s of the last century carried out an experiment aimed at studying the nuclei that are located in the nearest cosmic space. These measurements were carried out using proportional chambers and nuclear emulsions. They were carried out on the satellite of the Cosmos series. The scientists discovered the presence of N, O and Ne nuclei fluxes in outer space in which the orbit of an artificial satellite (inclination 52 °, altitude about 400-500 km) crossed the Brazilian anomaly.

As the analysis showed, these nuclei, whose energy reached several tens of MeV / nucleon, had no galactic, albedic or solar origin, since they could not penetrate into the magnetosphere of our planet with such energy. So scientists have discovered an anomalous component of cosmic rays captured by a magnetic field.

Low-energy atoms in interstellar matter are able to penetrate the heliosphere. Then the ultraviolet radiation of the Sun ionizes them once or twice. The resulting charged particles are accelerated at the fronts of the solar wind, reaching several tens of MeV / nucleon. Then they penetrate into the magnetosphere, in which they are captured and completely ionized.

Quasistationary belt of protons and electrons

On the Sun on March 22, 1991, a powerful flash happened, accompanied by the ejection of a huge mass of solar matter. It reached the magnetosphere by March 24 and changed its outer area. Particles of the solar wind, which had a large energy, burst into the magnetosphere. They reached the area in which CRESS was then, an American satellite. Installed on it, devices recorded a sharp increase in protons, whose energy was from 20 to 110 MeV, as well as powerful electrons (about 15 MeV). This indicated the appearance of a new belt. First, a quasi-stationary belt was observed on a number of spacecraft. However, only at Mir station it was studied during the entire lifetime, which is about two years.

By the way, in the 60s of the last century, as a result of the explosion of nuclear devices in space, a quasi-stationary belt consisting of electrons with small energies appeared. It lasted about 10 years. Radioactive fission fragments disintegrated, which was the source of charged particles.

Is there an RPG on the Moon

The satellite of our planet does not have a Van Allen radiation belt. In addition, he does not have a protective atmosphere. The surface of the moon is open to the sunny winds. A strong solar flare, if it occurred during a lunar expedition, would incinerate both astronauts and capsules, as a huge radiation flux would be released, which is fatal.

Is it possible to protect ourselves from cosmic radiation

This question has been of interest to scientists for many years. In small doses, radiation, as we know, practically does not affect the state of our health. However, it is safe only when it does not exceed a certain threshold. Do you know what level of radiation outside the Van Allen belt is on the surface of our planet? Usually the content of radon and thorium particles does not exceed 100 Bq per 1 m ³ . Inside the RPG, these indicators are much higher.

Undoubtedly, the radiation belts of Van Allen's Land are very dangerous for humans. Their impact on the body has been studied by many researchers. Soviet scientists in 1963 told Bernard Lowell, a famous British astronomer, that they do not know the means of protecting a person from the effects of radiation in space. This meant that even the thick-walled shells of the Soviet apparatus could not cope with it. How is the thin metal used in capsules of Americans, almost like a foil, able to protect astronauts?

According to NASA assurances, it sent astronauts to the moon only when it was not expected that the outbreaks that the organization is capable of predicting. This is what has made it possible to minimize the radiation hazard. Other specialists, however, say that one can only roughly predict the date of large emissions.

Belt of Van Allen and the flight to the Moon

Leonov, a Soviet cosmonaut, in 1966 still went into open space. However, he was dressed in an extra heavy lead suit. And in 3 years astronauts from the USA jumped on the lunar surface, and clearly not in heavy suits. Perhaps experts from NASA over the years managed to find an ultralight material that reliably protects astronauts from radiation? The flight to the moon still raises many questions. One of the main arguments of those who believe that the Americans did not land on it is the existence of radiation belts.