The Earth’s radiation belt (RPG), or Van Allen’s belt, is the region of outer space near our planet that looks like a ring in which there are giant streams of electrons and protons. Earth holds them with a dipole magnetic field.
Opening
RPZ was discovered in 1957-58. scientists from the United States and the USSR. Explorer-1 (pictured below), the first US space satellite to launch in 1958, provided very important data. Thanks to the on-board experiment conducted by the Americans above the surface of the Earth (at an altitude of about 1000 km), a radiation belt (internal) was found. Later, at a height of about 20,000 km, a second such zone was discovered. There is no clear boundary between the inner and outer zones - the first gradually passes into the second. These two zones of radioactivity differ in the degree of charge of the particles and their composition.
These areas began to be called Van Allen belts. James Van Allen is a physicist whose experiment helped to detect them. Scientists have found that these belts consist of the 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 shape that resembles a donut in shape).
Since then, many experiments have been conducted in space. They made it possible to study the main features and properties of RPZs. 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 U.S. interplanetary spacecraft near Mars. In addition, the Americans found it at Saturn and Jupiter.
Dipole magnetic field
Our planet has not only a Van Allen belt, but also a dipole magnetic field. It is a set of magnetic shells embedded in each other. The structure of this field resembles a head of cabbage or an onion. The magnetic shell can be imagined as a closed surface woven from magnetic lines of force. The closer the shell is to the center of the dipole, the greater the magnetic field becomes. In addition, the momentum that a charged particle needs to penetrate into it from the outside also increases.
So, the Nth shell has a particle momentum P n . In the case when the initial momentum of the particle does not exceed P n , a magnetic field reflects it. The particle then returns to outer space. However, it also happens that it appears on the Nth shell. In this case, she is no longer able to leave her. The trapped particle will be trapped until it scatters or, having collided with the residual atmosphere, loses energy.
In the magnetic field of our planet, the same shell is at different distances 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 region, magnetic lines of force are lowered, and trapped particles moving along them can be below 100 km in height, and therefore die in the earth's atmosphere.
RPZ composition
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 external. Therefore, at an early stage of the study, scientists believed that there are external (electronic) and internal (proton) radiation belts of the Earth. Currently, this opinion is no longer relevant.
The most significant mechanism for generating particles filling the Van Allen belt 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 without hindrance. However, they are unstable and easily decay into electrons, protons, and electron antineutrinos. High-energy radioactive albedo nuclei decay inside the capture zone. This is how the Van Allen belt is replenished with positrons and electrons.
RPZ and magnetic storms
When strong magnetic storms begin , these particles do not just accelerate, they leave the Van Allen radioactive belt, spilling out of it. The fact 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.
RPZ and the Northern Lights
The Van Allen 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) aurora is that the particles precipitate from the plasma layer, and also partially from the external RPG. Aurora borealis is the emission of atmospheric atoms, which are excited due to a collision with particles that have precipitated from the belt.
RPG research
Almost all the fundamental results of studies of such formations as radiation belts were obtained around the 1960s and 70s. Recent observations using orbital stations, interplanetary spacecraft and the latest scientific equipment have allowed scientists to obtain very important new information. Van Allen belts around the Earth continue to be studied in our time. Briefly tell about the most important achievements in this area.
Data received from Salyut-6
MEPhI researchers at the beginning of the 80s of the last century studied electron flows with high energy levels in the immediate vicinity of our planet. To do this, they used equipment that was located at the Salyut-6 orbital station. It allowed scientists to very 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, she still touched the inside of the Brazilian magnetic anomaly. At the intersection of this region, stationary flows consisting of high-energy electrons were found. Prior to this experiment, only electrons with an energy of not more than 5 MeV were recorded in the RPG.
Data of artificial satellites of the Meteor-3 series
MEPhI researchers carried out further measurements on artificial satellites of our planet of the Meteor-3 series, in which the height of circular orbits was 800 and 1200 km. This time, the device has penetrated deep into RPZ. He confirmed the results that were 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).
Discovery of the stationary CNO core belt
A group of researchers from the NNPI MSU in the late 80s and early 90s of the last century carried out an experiment aimed at studying the nuclei that are located in the nearest outer space. The measurement data were carried out using proportional chambers and nuclear emulsions. They were carried out on the Cosmos satellite. Scientists have discovered the presence of flows of N, O, and Ne nuclei in the space region in which the orbit of an artificial satellite (inclination 52 °, altitude about 400-500 km) crossed the Brazilian anomaly.
As analysis showed, these nuclei, whose energy reached several tens of MeV / nucleon, were not of galactic, albedo, or solar origin, since they could not penetrate deeply into the magnetosphere of our planet with such energy. So scientists discovered the anomalous component of cosmic rays captured by a magnetic field.
Low-energy atoms in interstellar matter can 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 the magnetosphere, in which they are captured and completely ionized.
Quasistationary belt of protons and electrons
A powerful flash occurred on March 22, 1991 in the Sun, which was accompanied by the release of a huge mass of solar matter. It reached the magnetosphere by March 24 and changed its outer region. Particles of the solar wind burst into the magnetosphere, which had great energy. They reached the area where CRESS, the American satellite, was then located. The devices installed on it recorded a sharp increase in protons, whose energy ranged from 20 to 110 MeV, as well as powerful electrons (about 15 MeV). This indicated the emergence of a new belt. First, a quasistationary belt was observed on a number of spacecraft. However, only at the Mir station it was studied over the entire life time of 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 quasistationary belt appeared, consisting of electrons with low energies. It existed for about 10 years. Radioactive fission fragments decayed, which was the source of charged particles.
Are there RPZs on the moon
The satellite of our planet does not have the Van Allen radiation belt. In addition, he does not have a protective atmosphere. The surface of the moon is exposed to solar winds. A strong solar flare, if it had occurred during the lunar expedition, would have incinerated both the astronauts and the capsule, since an enormous flux of radiation would occur, which is fatal.
Is it possible to protect yourself from cosmic radiation
This question has been of interest to scientists for many years. In small doses, radiation, as you know, has virtually no effect on 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? Typically, the content of particles of radon and thorium does not exceed 100 Bq per 1 m 3 . Within the RPG, these figures are much higher.
Of course, the radiation belts of Van Allen Earth are very dangerous to humans. Their effect on the body has been studied by many researchers. Soviet scientists in 1963 told Bernard Lovell, the famous British astronomer, that they did not know the means of protecting a person from the effects of radiation in space. This meant that even the thick-walled shells of Soviet apparatus could not cope with it. How did the finest metal used in American capsules, almost like foil, protect astronauts?
According to NASA, it sent astronauts to the moon only when flashes were not expected, which the organization is able to predict. This is what made it possible to minimize the radiation hazard. Other experts, however, argue that one can only roughly predict the date of large emissions.
Van Allen's belt and flight to the moon
Leonov, the Soviet cosmonaut, in 1966 still went out into outer space. However, he was wearing an extra heavy lead suit. And after 3 years, astronauts from the USA jumped on the lunar surface, and obviously not in heavy spacesuits. Perhaps NASA specialists over the years have managed to discover ultralight material that reliably protects astronauts from radiation? Flying 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.