Cosmic rays are elementary particles and atomic nuclei moving with high energies in outer space. Another definition: cosmic rays (cosmic radiation) are particles that fill interstellar space and constantly bombard the Earth.
Classification according to the origin of cosmic rays:
- outside our Galaxy
- · in the Galaxy
- · on the Sun
- · in interplanetary space
There are primary cosmic rays - these are cosmic rays before entering the atmosphere and secondary cosmic rays formed as a result of the processes of interaction of primary cosmic rays with the Earth's atmosphere.
Cosmic rays are a component of natural radiation (background radiation) on the Earth's surface and in the atmosphere.
Before the development of accelerator technology, cosmic rays served as the only source of high-energy elementary particles. Thus, the positron and muon were first found in cosmic rays.
By particle number, cosmic rays are 90 percent protons, 7 percent helium nuclei, about 1 percent heavier elements, and about 1 percent electrons. When studying the sources of cosmic rays outside the Solar System, the proton-nuclear component is mainly detected by the flux of gamma rays it creates by orbital gamma-ray telescopes, and the electron component is detected by the synchrotron radiation it generates, which occurs in the radio range (in particular, at meter waves - - when emitted in the magnetic field of the interstellar medium), and with strong magnetic fields in the area of the cosmic ray source - and to higher frequency ranges. Therefore, the electronic component can also be detected by ground-based astronomical instruments.
As a result of interaction with the nuclei of the atmosphere, primary cosmic rays (mainly protons) create a large number of secondary particles? pions, protons, neutrons, muons, electrons, positrons and photons. Thus, instead of one primary particle, a large number of secondary particles arise, which are divided into hadronic, muonic and electron-photon components.
Such a cascade covers a large area and is called a widespread air shower.
In one act of interaction, a proton usually loses ~50% of its energy, and as a result of the interaction, mainly pions are produced. Each subsequent interaction of the primary particle adds new hadrons to the cascade, which fly predominantly in the direction of the primary particle, forming the hadron core of the shower.
Muomn (from the Greek letter m used to denote) in the standard model of particle physics is an unstable elementary particle with a negative electric charge and spin 1?2.
Pion, pi-meson - three types of subatomic particles from the group of mesons. They are designated p0, p+ and p?. They have the smallest mass among mesons.
A positron is the antiparticle of an electron. It belongs to antimatter, has an electric charge of +1, a spin of 1/2, a lepton charge of 1 and a mass equal to the mass of an electron. When a positron and an electron annihilate, their mass is converted into energy in the form of two (and much less often, three or more) gamma quanta.
The resulting pions can interact with the nuclei of the atmosphere, or they can decay, forming the muon and electron-photon components of the shower. The hadronic component practically does not reach the Earth's surface, turning into muons, neutrinos and g-quanta.
The g-quanta formed during the decay of neutral pions cause a cascade of electrons and g-quanta, which in turn form electron-positron pairs. Charged leptons lose energy through ionization and radiative braking. The Earth's surface is mainly reached by relativistic muons. The electron-photon component is absorbed more strongly. One proton with energy > 1014 eV can create 106-109 secondary particles. On the Earth's surface, shower hadrons are concentrated in an area of the order of several meters; is the electron-photon component? in the area of ~100 m, muonic? several hundred meters. The cosmic ray flux at sea level is approximately 100 times less than the primary cosmic ray flux (~0.01 cm-2 s-1).
The main sources of primary cosmic rays are supernova explosions (galactic cosmic rays) and the Sun. High energies (up to 1016 eV) of galactic cosmic rays are explained by the acceleration of particles on shock waves generated by supernova explosions. The nature of ultra-high-energy cosmic rays does not yet have an unambiguous interpretation. The intensity of cosmic rays over large time intervals was constant for ~109 years. However, evidence has emerged that 30-40 thousand years ago the intensity of cosmic rays was noticeably different from today. The peak intensity is associated with an explosion close to the solar system.
primary cosmic ray
List of information sources
http://nuclphys.sinp.msu.ru/spargalka/039.htm
http://nuclphys.sinp.msu.ru/enc/e083.htm
https://ru.wikipedia.org/wiki/Cosmic_rays
https://ru.wikipedia.org/wiki/Pion_(particle)
https://ru.wikipedia.org/wiki/Muon
https://ru.wikipedia.org/wiki/Andron
https://ru.wikipedia.org/wiki/Positron
1. Cosmic rays (CR) are a stream of charged high-energy particles arriving at the Earth's surface approximately isotropically from all directions of outer space. There are primary and secondary cosmic rays.
Primary CL come to Earth from kosu0sa They include galactic CRs coming from galactic space, and solar CRs born on the Sun during flares.
Secondary CLs are born in the earth's atmosphere. They are formed during the interaction of primary cosmic rays with atoms of atmospheric matter.
The discovery of CL is connected!0 with the study of the electrical conductivity of air. At the beginning of the 20th century. it was reliably established that ^Y0" B0W, contained even in a sealed vessel, is always ionized. After the discovery of natural radioactivity, it became clear that the source of ionization is located outside the vessel containing air, and is radioactive radiation from rocks. This means that with increasing altitude, the ionization of air should decrease .
In 1912, the Austrian Victor Hess ascended in a hot air balloon, having an electroscope in a hermetically sealed vessel, the air pressure in which remained constant. He discovered that when ascending the first 600 m, the ionization of the air decreased. But, starting from 600 m, it began to increase the higher the faster. At an altitude of 4800 m, the concentration of ions became 4 times higher than at sea level. Therefore, Hess suggested that ionizing radiation of very high penetrating power falls on the boundary of the earth’s atmosphere from outer space.
Later experiments were carried out with balloons. It turned out that at an altitude of 8400 m, ionization is 10 times greater than at sea level. At an altitude of 20 km it reaches a maximum, and with further rise it begins to decrease. This is explained by the fact that at an altitude of 20 km, as a result of interaction (the atmosphere of primary CRs, the highest concentration of secondary ionizing particles is created.
2. Primary cosmic rays (PCR). Let us consider the energy spectrum, composition, range and mechanism of acceleration of particles in PCR
A. The PCL energy is very high. For most particles it exceeds 10 GeV. Therefore, the main task when detecting PCL particles is that the particles are decelerated within the detector. Only in this case can their total energy be measured.
For the first time, the energy spectrum of PCR could be directly measured on the Proton series satellites in 1965-69. Later, these measurements were repeated on the satellites of the Moon and Mars outside the Earth's magnetic field. The energy of PCL particles was measured using an ionization calorimeter. The device is a system of layers of nuclear targets, photographic plates and counters. Interacting with target nuclei (heavy metal), the cosmic particle generates a stream of hard γ quanta. In layers of lead, these γ quanta generate powerful avalanches of ionizing particles, which are recorded in photographic emulsions and counters. If the thickness of the layers of the calorimeter is large and all the particles of the avalanche remain in it, then by their number one can determine the energy of the primary cosmic particle. Ionization calorimeters have a volume of up to several cubic meters. meters and weight up to 20 tons.
Figure 166 shows the dependence of the intensity I of the flux of PCR particles on their energy E on a logarithmic scale. Intensity I is expressed by the number of particles per 1 m 2 of the earth's surface from a solid angle of 1 sr in 1 s. The energy E is given in gigaelectronvolts (1 GeV = 109V).
In the energy range E from 10 to 10 6 GeV, the energy spectrum is described by the empirical formula I = AE - γ, food A = 10 18 h/m 2 sr-s, γ = 1.6.
The total PCL flux is approximately 104 parts/m2 sr. The maximum energy of PCR reaches 10 11 GeV. This means that PCR is a unique source of ultra-high energies since the maximum energy obtained at accelerators does not exceed 10 5 GeV. But there are very few particles with energy E> 10 6 GeV. There is an average of one such particle per year per area of 1 m2.
PCL energy is of non-thermal origin. So, inside stars the average energy of particles is equal to Eср = 3kT/2 = 3*1.4*10 -23 *10 9 /2 = 2.1*10 -14 J=0.1 MeV. And the average energy of PCR particles near the Earth is 100 MeV, that is, 1000 times more. This means that cosmic particles are accelerated in some astrophysical processes of an electromagnetic nature.
b. Composition of PCL. Primary cosmic radiation at the location of the Solar System is isotropic in direction and constant in time. Based on its composition, PCL is divided into the following groups.
p-group. Contains hydrogen nuclei - protons 1 1 p, deuterons 2 1 D, tritons 3 1 T
α-group. Contains helium nuclei 4 2 He, 3 2 He.
L - group (from the English light - light). Contains light nuclei of lithium, beryllium and boron.
M-group (mesolight - medium light). Contains nuclei from carbon C to fluorine F.
H - group (heavy - heavy). Contains heavy nuclei from neon Ne to potassium K.
VH - group (very heavy - very heavy). Contains nuclei from calcium Ca (Z=20) to zinc Zn (z=30).
SH group (superheavy - super heavy). Contains nuclei starting with gallium Ca
E - group. Contains e electrons and e + positrons.
In contrast to the average content of elements in the Universe, an increased content of medium and heavy nuclei is observed in PCR: the group of medium nuclei L - 150,000 times, the H group - 2.5 times, the VH group - 60 times, the SH-n group 14 times .
The content of nuclei in the L group is especially noticeable. It can be assumed that the nuclei of the L group arise in PCRs as a result of collisions of nuclei with z> 6 with particles of interstellar gas, consisting mainly of hydrogen and helium. As a result of the fragmentation reaction, heavy nuclei are crushed and nuclei of group L are obtained. If we accept this hypothesis, then we can estimate the average path traversed by a cosmic particle from the place of its birth to the Earth.
V. Average path of particles in PCL. Let cosmic gas from hydrogen nuclei uniformly fill outer space. From a source generating heavy particles whose mass is greater than the mass of the group nuclei, a parallel beam of particles propagates along the OA1 axis. When heavy particles collide with hydrogen nuclei, light nuclei of group I are formed, moving in the same direction.
As a result of crushing of heavy particles, the intensity I t of the beam of heavy particles
should decrease with distance according to Bouguer's law, I t = I t0 exp(-σNx), (25.2) where I t is the initial intensity of the beam of heavy particles, N is the concentration of hydrogen nuclei in the cosmic gas. σ is the effective cross section of the nuclear fragmentation reaction with the formation of nuclei of group L. Let in each collision, when a heavy particle disappears, only one light particle of group L appears. The intensity of the particle flux I will increase with distance according to the law I e , = I 0 - I t = I T . (25.3) The ratio of the intensity of light and heavy particles in the PCL should increase with distance I l /I t = /exp(-σNx)= exp(-σNx)-1
Denoting the ratio I l /I t = n, we obtain: x = 1п(n + l)/σN. (25.5). Ratio n= I l /I t = 15/(52+15+4)=1/5=0.2. From astrophysical estimates, the concentration of dust grains - hydrogen nuclei in space is approximately equal to 1 particle per 1 cm 3, so n = 10 6 m -3. The effective cross section of fragmentation reactions observed under terrestrial conditions allows us to accept values σ = 10 -30 m 2. Hence x = ln(1.2)/10 -30 *10 6 =2*10 23 m.
Cosmic distances in astrophysics are usually expressed in parsecs. By definition, one parsec is the distance from which the diameter of the earth's orbit (150 million km) is visible at an angle of 1 second. A parsec is a very large distance, 1 ps = 3*10 16 m. Expressed in parsecs, the path of PCR particles to the Earth is x = 7000 kps.
Astrophysical studies have established that our galaxy has the shape of a biconvex lens with a diameter of 25 kpc and a thickness of up to 2 kpc, surrounded by a cosmic gas Halo in the shape of a ball. Comparison of the estimated value of x with the size of the Galaxy shows that x = 7000 kpc many times
greater not only than the diameter of the Galaxy (25 kpc), but also the diameter of the Halo (30 kpc). It follows that PCRs are born outside our Galaxy.
Apparently, this conclusion is not correct. Firstly, it was assumed that in each fragmentation reaction only one particle of group L is born. In fact, more of them can be born. Therefore, the increase in the flow of particles of group L can occur faster and at a smaller distance x. Secondly, it was assumed that in all collisions the direction of particle motion does not change. But that's not true. The nature of the motion of PCL particles is closer to the motion of Brownian particles. Their trajectory is a broken line. Therefore, PCR particles can travel much longer paths inside the Galaxy compared to its size.
More rigorous estimates lead to the conclusion that at least 90% of PCR particles (galactic rays) are born inside the Galaxy. And only about 10% of PCR particles come from outside the Galaxy (metagalactic rays). Due to the diffuse nature of the movement of cosmic particles, information about the position of sources of charged particles is erased. Therefore, cosmic radiation, with the exception of EM field quanta, is isotropic.
G. PCL particle acceleration mechanism. The most probable is Fermi's hypothesis. He suggested that during supernova explosions, extended magnetized clouds of plasma are formed, scattering from the epicenter of the explosion at enormous speeds. Charged particles in oncoming collisions with such clouds are reflected from them. In accordance with the law of conservation of momentum, the absolute radial component of the particle velocity increases by twice the speed of the cloud, υ 2 R = - υ 1 R + 2υ 0. If a particle catches up with a cloud, its speed decreases. But such particles can only be those that were born inside the star. And for those particles that are outside the star, counter motions are realized. Therefore, the kinetic energy of cosmic particles increases over time.
3. Origin of PKJI. There are 4 main sources of PCR: new stars,
supernovae, pulsars, quasars.
A. New stars (NS)- these are close binary star systems with a total mass of 1-5 solar masses, rotating around a common center of mass. Before the flare, they have a visual magnitude of 4-5 units.
During a flare, within 1-100 Earth days, their luminosity increases 100-1000000 times. After which, over the course of several years, it weakens to its original value. During the flare, the NS emits about 10 38 J of energy. Several years after the flare, a spherical gas shell with a radial expansion velocity = 1000 km/s is discovered at the site of the NS. The mass of the shell is about 0.01 solar mass, its kinetic energy is about 10 39 J.
The reason for the NS flare is that accretion occurs in the binary system - the flow of matter from a cold red dwarf to a hot white dwarf. As a result, in a hot star the balance between gravitational forces, on the one hand, and the forces of optical and gas-kinetic pressure, on the other, is disturbed. This leads to the explosion of a hot star.
NZ outbreaks are a common occurrence. 100-200 NS flare up in our Galaxy per year. They are not catastrophic in nature and are repeated in some stars after months and years. A certain proportion of PCL particles may originate from NS shells.
b. Supernovae (SNS). This is the name given to stars whose luminosity during a flare becomes commensurate with the luminosity of the galaxy to which it belongs. Thus, the SES of 1885, in the Andromeda nebula, had the luminosity of the entire galaxy. The amount of energy emitted during an NS flare is about 10 44 J. It is a million times greater than the energy of a NS flare. In our Galaxy, one SNS flares up on average once every 300 years. The last NOS was observed by Kepler in 1604 (Kepler's NOS).
The maximum luminosity of the SNS is 1-3 weeks. The shell ejected by the star has a mass up to 10 times the mass of the Sun and a speed of up to 20,000 km/s. Many PCL particles also originate from these shells. After the explosion of the SNS, nebulae and pulsars are discovered in their place. To date, about 90 remains of SNZ have been found. It can be assumed that the mechanism of formation of SNZs is based on a regularity: the greater the mass of atomic nuclei, the higher the temperature at which their thermonuclear fusion reaction occurs.
When a protostar emerges from a gas-dust nebula, the entire space of the nebula is filled with hydrogen. Due to the gravitational compression of the cloud, the temperature gradually increases. When the temperature reaches T = 10 7 K, a sluggish reaction of synthesis of protons into deuterons begins. The proton-proton cycle starts.
The protostar heats up to glow and turns into a star. Gravitational forces are balanced by the forces of light gas-kinetic pressure. Compression is paused. During the period of hydrogen combustion, relative equilibrium is established.
After the bulk of the hydrogen turns into helium, the star begins to cool, and the light pressure quickly decreases. The helium synthesis reaction does not start because the temperature T1 is not sufficient for the synthesis of helium nuclei. During the process of gravitational compression of a star, its temperature gradually increases. Gravity forces increase directly
is proportional to l/r 2, therefore, when the temperature T 1 is reached, equilibrium does not occur, since in this case the temperature T 1 corresponds to a smaller volume of the star. Compression and temperature growth continue, and at a certain temperature T 2 = 10 8 K the fusion reaction of helium nuclei starts: 3 4 2 He-> 12 6 C + 7.22 MeV (τ = 10 years), and further: (25.6)
4 2 He + 12 8 C-> 16 8 O + γ, 4 2 He + 16 8 O-> 20 10 Ne+ γ, 4 2 He+ 20 10 Ne -> 24 12 Mg. (25.7)
After helium burns out, a dense star core is formed, the core content of carbon is C-12, oxygen 0-16, neon Ne-20, magnesium Mg-24. Further, the evolution of the star can proceed in a similar way. At a certain temperature T 3 > T 2, the synthesis reaction of carbon-magnesium nuclei is excited. This cycle should end with the formation of silicon nuclei Si-26 and phosphorus P-31.
And finally, at a temperature T 4 > T 3, the last stage of the exothermic reaction of the synthesis of silicon and phosphorus nuclei can be excited, which should end with the formation of nuclei 56 26 Fe, 59 27 Co, 57 28 Ni.
This is an idealized scheme. In fact, these processes may overlap. In the center of the star there can be reactions of fusion of heavier nuclei at higher temperatures, and at the periphery there can be reactions of fusion of less heavy nuclei at lower temperatures. And in most cases, the evolution of a star proceeds calmly. But sometimes such a combination of mass, composition, size and other parameters of a star arises that the balance is upset. Under the influence of gravity, the star's matter rapidly moves towards the center, causing the collapse of the star. The high density, temperature and pressure in the core of a star can lead in some cases to the rapid release of enormous energies. For example, as a result of this reaction: 16 8 O+ 16 8 O= 32 16 S+16.5 MeV. (25.8)
The star explodes, giving birth to a supernova. If we take into account the energy of the SES explosion E = 10 44 J and the frequency of their repetitions, it turns out that to maintain the average PCL energy density, 1% of the SES explosion is sufficient.
V. Pulsars(pulsating sources of radio emission) are small neutron stars, up to 20 km in diameter, resulting from the rapid gravitational compression of supernova remnants. The density of neutron stars reaches 1012 kg/m 3, which is close to the density of the matter of atomic nuclei.
As a result of the compression of the remnants of the star, the magnetic field induction on the surface reaches enormous values of the order of 10 9 Tesla. For comparison: the maximum magnetic field induction obtained in a physical experiment (in pulsed solenoids) does not exceed 10 2 Tesla. Due to their small size, the rotation speed of neutron stars can reach 1000 Hz. Such a rapidly rotating magnetic star induces a vortex electric field around itself. This field accelerates particles of the plasma surrounding the pulsar to high energies. Nuclei are accelerated to 10 20 eV, electrons - to 10 12 eV. After leaving the pulsar, these fast particles replenish the PCR composition.
Charged particles flying from space into the magnetic field of a pulsar swirl around field lines, emitting synchrotron radiation in the radio range. This radiation is especially strong in the direction of the magnetic poles. Since the pulsar's rotation axis does not coincide with the magnetic axis, the radio beam describes a cone. If the Earth is in the wall of this cone, then a signal is periodically recorded on it at the moment when the polar beam of radio emission crosses the Earth.
Due to energy loss, the period of pulsars increases. Therefore, the younger the pulsar, the higher the frequency of its rotation. Currently, several hundred pulsars are known, their periods range from 0.033 s to 4.8 s.
city of Quasars(short for quasi-stellar radio source) - quasi-stars similar to stars. They are similar to stars in optical appearance and similar to nebulae in the nature of their spectra. The spectra of quasars exhibit a huge redshift, 2-6 times greater than the largest known in the Galaxy. In the visible range, for example, the leading UV line of the Lyman series is observed (D = 121.6 nm in the reference frame of the emitting gas).
By determining the Doppler frequency shift formula ν=ν 0 √((1±β)/(1-+β)), where β=υ/s, the radial velocity υ of the quasar relative to the Earth, and using Hubble’s empirical law υ = Нr, where H=1.3-10 -18 s -1 is the Hubble constant, you can calculate the distance to the quasar. The distances to the quasar turned out to be gigantic. Their order is r~10 10 ps. This is a million times the size of our Galaxy. The brightness of quasars changes with a period T of about 1 hour. Since the diameter of a quasar cannot exceed c*T, where c is the speed of light in vacuum, it turns out that the size of quasars is small, no more than the diameter of the orbit of Uranus (4*10 12 m). Taking into account the great distance of quasars, it turns out that they must emit a gigantic power of the order of 10 45 W, comparable to Galaxies, in a relatively small volume of space. Such super-powerful objects should emit streams of high-energy particles into space. The energy mechanism of quasars is unclear. With such a huge energy consumption, the active stage of quasars should be limited to 10 thousand years. To date, among optical objects, about 200 are considered quasars.
4. Solar cosmic rays. The Sun is the closest star to Earth. This star is in a stationary state and therefore is not a noticeable source of PCR on the Galaxy scale. But since the Earth is very close to the Sun, it is within the reach of the plasma flowing from the Sun - the solar wind. The solar wind consists of protons and electrons. It originates in ascending gas-dynamic flows - torches in the photosphere layer and develops in the chromosphere.
The energy of solar wind particles is very small compared to galactic rays: for electrons E≈10 4 eV, for protons no more than 10 11 N eV. During the activation of explosive processes on the surface of the Sun (the period of solar activity), the concentration of particles in the solar wind in Earth's orbit is hundreds of times higher than the concentration of particles in galactic rays. Therefore, the influence of the solar wind on terrestrial processes during solar activity is much more noticeable compared to galactic rays. At this time, radio communications are disrupted, geomagnetic storms and auroras occur. But on average, the contribution of solar cosmic rays to Earth is small. It is 1-3% in intensity.
5. Secondary cosmic rays is a stream of particles produced during the interaction of PCR with matter in the earth's atmosphere. Often, the passage of a particle in a substance is characterized by its average path l before interacting with the core of the medium. The average range is often expressed by the mass of a substance in a column with an area of 1 cm2 and a height l. Thus, the entire thickness of the earth’s atmosphere is 1000 g/cm2. For protons, the range l corresponds to 70-80 g/cm 2, for α-particles - 25 g/cm 2, for heavier nuclei this value is even less. The probability of a proton reaching the earth's surface is found from Bouguer's law. I/I 0 =exp(-x/l)=exp(-1000/70)≈10 -7. Out of 10 million primary protons, only one will reach the Earth. For α particles and nuclei this number is even smaller. There are 3 components in secondary cosmic rays: nuclear-active (hadron), hard (muon) and soft (electron-photon).
A. Nuclear active component contains protons and neutrons that arise from the interaction of protons and other high-energy PCR particles E 0 >1 GeV with the nuclei of atoms in the earth's atmosphere, mainly nitrogen N and oxygen O. When a particle hits a nucleus, approximately half of its energy is spent on knocking out several nucleons with energies E≈0.2 GeV, on the excitation of the final nucleus and on the multiple production of relativistic particles. These are mainly pions π +, π 0, π -. Their number per primary proton with energy E 0 ≈0.2 GeV can reach up to 10. The excited nucleus, decaying, emits several more nucleons or α-particles. The born nucleons and the primary particle, interacting with the nuclei of the atmosphere, lead to the development of a nuclear cascade. Protons and other low-energy contaminated particles appearing in each collision event quickly slow down and are absorbed as a result of ionization losses. Neutrons participate in the further multiplication of nuclear-active particles down to the lowest energies.
b. Hard (muon) component is born in a nuclear cascade from charged pions with energy E≤100 GeV, decaying according to the scheme: π ± →μ ± + ν μ (ṽ μ), where μ ± are charged muons. Their rest mass is 207m e, and the average lifetime in their own frame of reference is τ 0 =2*10 6 s; ν m (ṽ m) - muon neutrino (antineutrino). Muons, in turn, decay according to the scheme: μ - →e - *ṽ, μ + →e + *ν. Since the speeds of muons are close to the speed of light, then, in accordance with the theory of relativity, their average lifetime in the reference frame associated with the Earth turns out to be quite large. As a result, muons manage to travel through the entire atmosphere and even about 20 m of soil. This is also due to the fact that muons, and especially neutrinos, weakly interact with matter. That is why the flux of muons and neutrinos is called the hard or penetrating component of secondary cosmic rays.
e. Soft (electron-photon) component. Its main source is neutral pions π 0 formed in a nuclear collision. Compared to charged pions π + and π -, whose lifetime is 2*10 -6 s, neutral pions decay faster, their average lifetime τ=1.8*10 -16 s. From the place of its birth, the π 0 -pion manages to move to an insignificant distance x≈c*τ= 3*10 8 *1.8*10 -16 = 5*10 -8 m and decays into two high-energy γ-quanta: π0 → γ + γ. These energetic γ-quanta in the field of nuclei decay into electron-positron pairs, γ→ e - + e +. Each of the resulting electrons has a high speed and, when colliding with nuclei, emits bremsstrahlung γ-quanta, e - → e - + γ.. And so on. An avalanche-like process occurs.
An increase in the number of electrons, positrons and γ-quanta will occur until the energy of the particles decreases to a value of 72 MeV. After this, the predominant energy losses occur through the ionization of atoms in particles and Compton scattering in γ quanta. The growth of the number of particles in the shower stops, and its individual particles are absorbed. The maximum development of the soft component occurs at an altitude of about 15 km.
At very high energies of primary particles E 0 >. 10 5 GeV electron-photon cascade avalanches in the earth's atmosphere acquire the specific features of extensive atmospheric showers. The development of such a shower begins at an altitude of 20-25 km. The total number of particles can reach 10 8 -10 9 . Since one particle in a shower has approximately 1 GeV of energy, the energy of the primary particle can be estimated from the number of particles in the shower.
The existence of such cascading showers was discovered in 1938 by the Frenchman Pierre Auger. That's why they are often called Auger showers.
Material from Wikipedia - the free encyclopedia
Cosmic rays- elementary particles and atomic nuclei moving with high energies in outer space.
Basics
Cosmic ray physics considered to be part high energy physics And particle physics.
Physics of cosmic rays studies:
- processes leading to the emergence and acceleration of cosmic rays;
- cosmic ray particles, their nature and properties;
- phenomena caused by cosmic ray particles in outer space, the atmosphere of the Earth and planets.
Studying the flows of high-energy charged and neutral cosmic particles falling on the boundary of the Earth's atmosphere is the most important experimental task.
Classification according to the origin of cosmic rays:
- outside our Galaxy
- in the Galaxy
- in the sun
- in interplanetary space
Primary It is customary to call extragalactic and galactic rays. Secondary It is customary to call particle flows passing and transforming in the Earth’s atmosphere.
Cosmic rays are a component of natural radiation (background radiation) on the Earth's surface and in the atmosphere.
Before the development of accelerator technology, cosmic rays served as the only source of high-energy elementary particles. Thus, the positron and muon were first found in cosmic rays.
The energy spectrum of cosmic rays consists of 43% energy from protons, another 23% from helium energy (alpha particles) and 34% energy transferred by other particles.
By particle number, cosmic rays are 92% protons, 6% helium nuclei, about 1% heavier elements, and about 1% electrons. When studying sources of cosmic rays outside the Solar System, the proton-nuclear component is mainly detected by the flux of gamma rays it creates by orbital gamma-ray telescopes, and the electron component is detected by the synchrotron radiation it generates, which occurs in the radio range (in particular, at meter waves - at radiation in the magnetic field of the interstellar medium), and with strong magnetic fields in the region of the cosmic ray source - and to higher frequency ranges. Therefore, the electronic component can also be detected by ground-based astronomical instruments.
Traditionally, particles observed in cosmic rays are divided into the following groups: (respectively, protons, alpha particles, light, medium, heavy and superheavy). A feature of the chemical composition of primary cosmic radiation is the anomalously high (several thousand times) content of group L nuclei (lithium, beryllium, boron) compared to the composition of stars and interstellar gas. This phenomenon is explained by the fact that the mechanism of generation of cosmic particles primarily accelerates heavy nuclei, which, when interacting with protons of the interstellar medium, decay into lighter nuclei. This assumption is confirmed by the fact that cosmic rays have a very high degree of isotropy.
History of cosmic ray physics
The first indication of the possibility of the existence of ionizing radiation of extraterrestrial origin was obtained at the beginning of the 20th century in experiments studying the conductivity of gases. The detected spontaneous electric current in the gas could not be explained by ionization arising from the natural radioactivity of the Earth. The observed radiation turned out to be so penetrating that a residual current was still observed in the ionization chambers, shielded by thick layers of lead. In 1911-1912, a number of experiments were carried out with ionization chambers on balloons. Hess discovered that radiation increases with altitude, whereas ionization caused by the radioactivity of the Earth should decrease with altitude. Colherster's experiments proved that this radiation is directed from top to bottom.
In 1921-1925, the American physicist Millikan, studying the absorption of cosmic radiation in the Earth's atmosphere depending on the observation altitude, discovered that in lead this radiation is absorbed in the same way as gamma radiation from nuclei. Millikan was the first to call this radiation cosmic rays. In 1925, Soviet physicists L.A. Tuvim and L.V. Mysovsky measured the absorption of cosmic radiation in water: it turned out that this radiation was absorbed ten times less than the gamma radiation of nuclei. Mysovsky and Tuwim also discovered that the intensity of radiation depends on barometric pressure - they discovered the “barometric effect”. D.V. Skobeltsyn's experiments with a cloud chamber placed in a constant magnetic field made it possible to “see”, due to ionization, traces (tracks) of cosmic particles. D. V. Skobeltsyn discovered showers of cosmic particles. Experiments in cosmic rays have made it possible to make a number of fundamental discoveries for the physics of the microworld.
Solar cosmic rays
Solar cosmic rays (SCR) are energetic charged particles - electrons, protons and nuclei - injected by the Sun into interplanetary space. The SCR energy ranges from several keV to several GeV. At the lower end of this range, SCRs are confined to protons from high-speed solar wind streams. SCR particles appear as a result of solar flares.
Ultra-high energy cosmic rays
The energy of some particles exceeds the GZK (Greisen - Zatsepin - Kuzmin) limit - the theoretical energy limit for cosmic rays 5·10 19 eV, caused by their interaction with photons of the cosmic microwave background radiation. Several dozen such particles were recorded by the AGASA observatory over the course of a year. (English)Russian. These observations do not yet have a sufficiently substantiated scientific explanation.
Detection of cosmic rays
For a long time after the discovery of cosmic rays, the methods for registering them did not differ from the methods for registering particles in accelerators, most often gas-discharge counters or nuclear photographic emulsions raised into the stratosphere or into outer space. But this method does not allow systematic observations of high-energy particles, since they appear quite rarely, and the space in which such a counter can conduct observations is limited by its size.
Modern observatories operate on different principles. When a high-energy particle enters the atmosphere, it interacts with air atoms in the first 100 g/cm², giving rise to a flurry of particles, mainly pions and muons, which, in turn, give birth to other particles, and so on. A cone of particles is formed, which is called a shower. Such particles move at speeds exceeding the speed of light in air, resulting in Cherenkov glow, which is detected by telescopes. This technique makes it possible to monitor areas of the sky covering hundreds of square kilometers.
Implications for spaceflight
ISS astronauts, when they close their eyes, see flashes of light no more than once every 3 minutes; perhaps this phenomenon is associated with the impact of high-energy particles entering the retina. However, this has not been experimentally confirmed; it is possible that this effect has exclusively psychological foundations.
Long-term exposure to cosmic radiation can have a very negative impact on human health. For the further expansion of humanity to other planets of the solar system, reliable protection against such dangers should be developed - scientists from Russia and the USA are already looking for ways to solve this problem.
See also
- Observatory Pierre Auger ( English)
Write a review about the article "Cosmic rays"
Notes
- // Physical encyclopedia / Ch. ed. A. M. Prokhorov. - M.: Great Russian Encyclopedia, 1990. - T. 2. Quality factor - Magneto-optics. - pp. 471-474. - 703 p. - ISBN 5852700614.
- Ginzburg V.L. , Syrovatsky S.I. Current state of the question about the origin of cosmic rays // Phys. - 1960. - No. 7.- P. 411-469. - ISSN 1996-6652. - URL: ufn.ru/ru/articles/1960/7/b/
- , With. 18.
- V. L. Ginzburg Cosmic rays: 75 years of research and prospects for the future // Earth and the Universe. - M.: Nauka, 1988. - No. 3. - P. 3-9.
- , With. 236.
Literature
- S. V. Murzin. Introduction to cosmic ray physics. M.: Atomizdat, 1979.
- Model of outer space - M.: Moscow State University Publishing House, in 3 volumes.
- A. D. Filonenko(Russian) // UFN. - 2012. - T. 182. - pp. 793-827.
- Dorman L.I. Experimental and theoretical foundations of cosmic ray astrophysics. - M.: Nauka, 1975. - 464 p.
- ed. Shirkov D.V. Physics of the microworld. - M.: Soviet Encyclopedia, 1980. - 528 p.
Links
|
||||||||||||||||||||||||
Excerpt characterizing cosmic rays
At this time, Petya, to whom no one was paying attention, approached his father and, all red, in a breaking voice, sometimes rough, sometimes thin, said:“Well, now, daddy, I will decisively say - and mummy too, whatever you want - I will decisively say that you will let me into military service, because I can’t ... that’s all ...
The Countess raised her eyes to the sky in horror, clasped her hands and angrily turned to her husband.
- So I agreed! - she said.
But the count immediately recovered from his excitement.
“Well, well,” he said. - Here’s another warrior! Stop the nonsense: you need to study.
- This is not nonsense, daddy. Fedya Obolensky is younger than me and is also coming, and most importantly, I still can’t learn anything now that ... - Petya stopped, blushed until he sweated and said: - when the fatherland is in danger.
- Complete, complete, nonsense...
- But you yourself said that we would sacrifice everything.
“Petya, I’m telling you, shut up,” the count shouted, looking back at his wife, who, turning pale, looked with fixed eyes at her youngest son.
- And I’m telling you. So Pyotr Kirillovich will say...
“I’m telling you, it’s nonsense, the milk hasn’t dried yet, but he wants to go into military service!” Well, well, I’m telling you,” and the count, taking the papers with him, probably to read them again in the office before resting, left the room.
- Pyotr Kirillovich, well, let’s go have a smoke...
Pierre was confused and indecisive. Natasha's unusually bright and animated eyes, constantly turning to him more than affectionately, brought him into this state.
- No, I think I’ll go home...
- It’s like going home, but you wanted to spend the evening with us... And then you rarely came. And this one of mine...” the count said good-naturedly, pointing at Natasha, “she’s only cheerful when she’s with you...”
“Yes, I forgot... I definitely need to go home... Things to do...” Pierre said hastily.
“Well, goodbye,” said the count, completely leaving the room.
- Why are you leaving? Why are you upset? Why?..” Natasha asked Pierre, looking defiantly into his eyes.
“Because I love you! - he wanted to say, but he didn’t say it, he blushed until he cried and lowered his eyes.
- Because it’s better for me to visit you less often... Because... no, I just have business.
- Why? no, tell me,” Natasha began decisively and suddenly fell silent. They both looked at each other in fear and confusion. He tried to grin, but could not: his smile expressed suffering, and he silently kissed her hand and left.
Pierre decided not to visit the Rostovs with himself anymore.
Petya, after receiving a decisive refusal, went to his room and there, locking himself away from everyone, wept bitterly. They did everything as if they had not noticed anything, when he came to tea, silent and gloomy, with tear-stained eyes.
The next day the sovereign arrived. Several of the Rostov courtyards asked to go and see the Tsar. That morning Petya took a long time to get dressed, comb his hair and arrange his collars like the big ones. He frowned in front of the mirror, made gestures, shrugged his shoulders, and finally, without telling anyone, he put on his cap and left the house from the back porch, trying not to be noticed. Petya decided to go straight to the place where the sovereign was and directly explain to some chamberlain (it seemed to Petya that the sovereign was always surrounded by chamberlains) that he, Count Rostov, despite his youth, wanted to serve the fatherland, that youth could not be an obstacle for devotion and that he is ready... Petya, while he was getting ready, prepared many wonderful words that he would say to the chamberlain.
Petya counted on the success of his presentation to the sovereign precisely because he was a child (Petya even thought how everyone would be surprised at his youth), and at the same time, in the design of his collars, in his hairstyle and in his sedate, slow gait, he wanted to present himself as an old man. But the further he went, the more he was amused by the people coming and going at the Kremlin, the more he forgot to observe the sedateness and slowness characteristic of adult people. Approaching the Kremlin, he already began to take care that he would not be pushed in, and resolutely, with a threatening look, put his elbows out to his sides. But at the Trinity Gate, despite all his determination, people who probably did not know for what patriotic purpose he was going to the Kremlin, pressed him so hard against the wall that he had to submit and stop until the gate with a buzzing sound under the arches the sound of carriages passing by. Near Petya stood a woman with a footman, two merchants and a retired soldier. After standing at the gate for some time, Petya, without waiting for all the carriages to pass, wanted to move on ahead of the others and began to decisively work with his elbows; but the woman standing opposite him, at whom he first pointed his elbows, angrily shouted at him:
- What, barchuk, you are pushing, you see - everyone is standing. Why climb then!
“So everyone will climb in,” said the footman and, also starting to work with his elbows, he squeezed Petya into the stinking corner of the gate.
Petya wiped the sweat that covered his face with his hands and straightened his sweat-soaked collars, which he had arranged so well at home, like the big ones.
Petya felt that he had an unpresentable appearance, and was afraid that if he presented himself like that to the chamberlains, he would not be allowed to see the sovereign. But there was no way to recover and move to another place due to the cramped conditions. One of the passing generals was an acquaintance of the Rostovs. Petya wanted to ask for his help, but thought that it would be contrary to courage. When all the carriages had passed, the crowd surged and carried Petya out to the square, which was completely occupied by people. Not only in the area, but on the slopes, on the roofs, there were people everywhere. As soon as Petya found himself in the square, he clearly heard the sounds of bells and joyful folk talk filling the entire Kremlin.
At one time the square was more spacious, but suddenly all their heads opened, everything rushed forward somewhere else. Petya was squeezed so that he could not breathe, and everyone shouted: “Hurray! Hurray! hurray! Petya stood on tiptoes, pushed, pinched, but could not see anything except the people around him.
There was one common expression of tenderness and delight on all faces. One merchant's wife, standing next to Petya, was sobbing, and tears flowed from her eyes.
- Father, angel, father! – she said, wiping away tears with her finger.
- Hooray! - they shouted from all sides. For a minute the crowd stood in one place; but then she rushed forward again.
Petya, not remembering himself, clenched his teeth and brutally rolled his eyes, rushed forward, working with his elbows and shouting “Hurray!”, as if he was ready to kill himself and everyone at that moment, but exactly the same brutal faces climbed from his sides with the same shouts of “Hurray!”
“So this is what a sovereign is! - thought Petya. “No, I can’t submit a petition to him myself, it’s too bold!” Despite this, he still desperately made his way forward, and from behind the backs of those in front he glimpsed an empty space with a passage covered with red cloth; but at that time the crowd wavered back (in front the police were pushing away those who were advancing too close to the procession; the sovereign was passing from the palace to the Assumption Cathedral), and Petya unexpectedly received such a blow to the side in the ribs and was so crushed that suddenly everything in his eyes became blurred and he lost consciousness. When he came to his senses, some kind of clergyman, with a bun of graying hair back, in a worn blue cassock, probably a sexton, held him under his arm with one hand, and with the other protected him from the pressing crowd.
- The youngster was run over! - said the sexton. - Well, that’s it!.. it’s easier... crushed, crushed!
The Emperor went to the Assumption Cathedral. The crowd smoothed out again, and the sexton led Petya, pale and not breathing, to the Tsar’s cannon. Several people took pity on Petya, and suddenly the whole crowd turned to him, and a stampede began around him. Those who stood closer served him, unbuttoned his frock coat, placed a gun on the dais and reproached someone - those who crushed him.
“You can crush him to death this way.” What is this! To do murder! “Look, cordial, he’s become white as a tablecloth,” said the voices.
Petya soon came to his senses, the color returned to his face, the pain went away, and for this temporary trouble he received a place on the cannon, from which he hoped to see the sovereign who was about to return. Petya no longer thought about submitting a petition. If only he could see him, he would consider himself happy!
During the service in the Assumption Cathedral - a combined prayer service on the occasion of the arrival of the sovereign and a prayer of thanks for the conclusion of peace with the Turks - the crowd spread out; Shouting sellers of kvass, gingerbread, and poppy seeds appeared, which Petya was especially keen on, and ordinary conversations could be heard. One merchant's wife showed her torn shawl and said how expensive it was bought; another said that nowadays all silk fabrics have become expensive. The sexton, Petya’s savior, was talking with the official about who and who was serving with the Reverend today. The sexton repeated the word soborne several times, which Petya did not understand. Two young tradesmen joked with the courtyard girls gnawing nuts. All these conversations, especially jokes with girls, which had a special attraction for Petya at his age, all these conversations did not interest Petya now; ou sat on his gun dais, still worried at the thought of the sovereign and his love for him. The coincidence of the feeling of pain and fear when he was squeezed with a feeling of delight further strengthened in him the awareness of the importance of this moment.
Suddenly, cannon shots were heard from the embankment (they were firing to commemorate peace with the Turks), and the crowd quickly rushed to the embankment to watch them shoot. Petya also wanted to run there, but the sexton, who had taken the little bark under his protection, did not let him in. The shots still continued when officers, generals, and chamberlains ran out of the Assumption Cathedral, then others came out not so hastily, the caps were taken off their heads again, and those who had run away to look at the cannons ran back. Finally, four more men in uniforms and ribbons emerged from the cathedral doors. "Hooray! Hooray! – the crowd shouted again.
- Which? Which? - Petya asked around him in a crying voice, but no one answered him; everyone was too carried away, and Petya, choosing one of these four faces, whom he could not clearly see because of the tears that had come into his eyes with joy, concentrated all his delight on him, although it was not the sovereign, shouted “Hurray! in a frantic voice and decided that tomorrow, no matter what it cost him, he would be a military man.
The crowd ran after the sovereign, accompanied him to the palace and began to disperse. It was already late, and Petya had not eaten anything, and sweat poured from him like hail; but he did not go home and, together with a diminished, but still quite large crowd, stood in front of the palace, during the sovereign’s dinner, looking out the palace windows, expecting something else and equally envying the dignitaries who were driving up to the porch - for the sovereign’s dinner, and the chamber lackeys who served at the table and flashed through the windows.
At the sovereign’s dinner, Valuev said, looking out the window:
“The people still hope to see your Majesty.”
Lunch was already over, the sovereign got up and, finishing his biscuit, went out onto the balcony. The people, with Petya in the middle, rushed to the balcony.
-Angel, father! Hurray, father!.. - the people and Petya shouted, and again the women and some weaker men, including Petya, began to cry with happiness. A rather large piece of the biscuit, which the sovereign was holding in his hand, broke off and fell onto the railing of the balcony, from the railing to the ground. The driver standing closest to him in his undershirt rushed to this piece of biscuit and grabbed it. Some of the crowd rushed to the coachman. Noticing this, the sovereign ordered a plate of biscuits to be served and began throwing biscuits from the balcony. Petya's eyes became bloodshot, the danger of being crushed excited him even more, he threw himself on the biscuits. He didn’t know why, but he had to take one biscuit from the king’s hands, and he had to not give in. He rushed and knocked down an old woman who was catching a biscuit. But the old woman did not consider herself defeated, although she was lying on the ground (the old woman was catching the biscuits and did not get them with her hands). Petya knocked her hand away with his knee, grabbed the biscuit and, as if afraid of being late, again shouted “Hurray!”, in a hoarse voice.
The Emperor left, and after that most of the people began to disperse.
“I said that we would have to wait a little longer, and so it happened,” people said joyfully from different sides.
No matter how happy Petya was, he was still sad to go home and know that all the pleasure of that day was over. From the Kremlin, Petya did not go home, but to his comrade Obolensky, who was fifteen years old and who also joined the regiment. Returning home, he resolutely and firmly announced that if they didn’t let him in, he would run away. And the next day, although he had not yet completely given up, Count Ilya Andreich went to find out how to settle Petya somewhere safer.
On the morning of the 15th, the third day after this, countless carriages stood at the Slobodsky Palace.
The halls were full. In the first there were noblemen in uniforms, in the second merchants with medals, beards and blue caftans. There was a hum and movement throughout the hall of the Noble Assembly. At one large table, under the portrait of the sovereign, the most important nobles sat on chairs with high backs; but most of the nobles walked around the hall.
All the nobles, the same ones whom Pierre saw every day, either in the club or in their houses, were all in uniforms, some in Catherine’s, some in Pavlov’s, some in the new Alexandrov’s, some in the general noble, and this general character of the uniform gave something strange and fantastic to these old and young, the most diverse and familiar faces. Particularly striking were the old people, low-sighted, toothless, bald, covered in yellow fat or wrinkled and thin. For the most part, they sat in their seats and were silent, and if they walked and talked, they joined someone younger. Just like on the faces of the crowd that Petya saw in the square, on all these faces there was a striking feature of the opposite: a general expectation of something solemn and ordinary, yesterday - the Boston party, Petrushka the cook, Zinaida Dmitrievna’s health, etc.
Pierre, who had been wearing an awkward nobleman's uniform that had become too tight for him since early morning, was in the halls. He was excited: the extraordinary gathering of not only the nobility, but also the merchants - the estates, etats generaux - evoked in him a whole series of thoughts that had long been abandoned, but were deeply etched in his soul about the Contrat social [Social Contract] and the French Revolution. The words he noticed in the appeal that the sovereign would arrive in the capital to confer with his people confirmed him in this view. And he, believing that in this sense something important was approaching, something that he had been waiting for a long time, walked around, looked closely, listened to the conversation, but nowhere did he find the expression of the thoughts that occupied him.
Cosmic rays are usually called a set of flows of high-energy atomic nuclei, mainly protons, falling onto the Earth from outer space, and the secondary radiation they generate in the Earth’s atmosphere, in which all currently known elementary particles are found.
§ 54. DISCOVERY OF COSMIC RAYS
Research into cosmic rays began in the early years of this century in connection with the study of the cause of the continuous leakage of charge from electroscopes. The hermetically sealed electroscope discharged even with the most perfect insulation.
In 1910-1925. Various experiments in balloons and underground have shown that the cause of this is some strongly penetrating radiation, which originates somewhere outside the Earth and whose intensity decreases as it penetrates into the atmosphere. It causes ionization of the air in the ionization chamber and the associated discharge of electroscopes. Millikan called this stream of radiation cosmic rays.
In further experiments, a change in the intensity of cosmic radiation (particle flux density) was established depending on the observation altitude (Fig. 105).
Rice. 105. Dependence of the number of cosmic particles on height in relative units)
The intensity of cosmic rays increases relatively quickly up to approximately altitude above sea level, then the growth rate
slows down and at altitude the intensity reaches its maximum value. When rising to high altitudes, its decrease is observed, and starting from altitude, the intensity of cosmic rays remains constant. As a result of numerous experiments, it has been established that cosmic rays arrive on the surface of the Earth from all sides evenly and there is no place in the Universe that could be called a source of cosmic rays.
Many fundamentally important discoveries have been made in the study of cosmic rays. Thus, in 1932, Anderson discovered a positron in cosmic rays, predicted by Dirac's theory. In 1937, Anderson and Niedermayer discovered -mesons and indicated the type of their decay. In 1947, Powell discovered -mesons, which, according to Yukawa's theory, were necessary to explain nuclear forces. In 1955, the presence of K-mesons in cosmic rays was established, as well as heavy neutral particles with a mass exceeding the mass of a proton - hyperons. Research into cosmic rays led to the introduction of a quantum characteristic called strangeness. Experiments with cosmic rays also raised the question of the possibility of parity nonconservation. Processes of multiple generation of particles in a single collision event were discovered for the first time in cosmic rays.
Research in recent years has made it possible to determine the effective cross section for the interaction of high-energy nucleons with nuclei. Since cosmic rays contain particles with energies reaching up to 100, cosmic rays are the only source of information about the interaction of particles of such high energy.
The use of rockets and artificial satellites in the study of cosmic rays led to new discoveries - the discovery of the Earth's radiation belts. The ability to study primary cosmic radiation beyond the Earth's atmosphere has created new methods for studying galactic and intergalactic space. Thus, studies of cosmic rays, having moved from the field of geophysics to the field of nuclear physics and elementary particle physics, now closely combine the study of the structure of the microcosm with the problems of astrophysics.
In connection with the creation of accelerators with energies in the tens, the center of gravity of the nuclear direction in cosmic ray physics has moved to the region of ultra-high energies, where studies of nuclear interactions, the structure of nucleons and other elementary particles continue. In addition, an independent direction arose - the study of cosmic rays in geophysical and astrophysical aspects. The subject of research here is: primary cosmic rays near the Earth (chemical composition, energy spectrum, spatial distribution); solar rays (their generation, movement to the Earth and influence on the earth's
ionosphere); the influence of the interplanetary and interstellar medium and magnetic fields on cosmic rays; radiation belts near the Earth and other planets; origin of cosmic rays. The most important means of studying these problems is a detailed study of the various variations in the flux of cosmic rays observed on the Earth and near it.
Boris Arkadyevich Khrenov,
Doctor of Physical and Mathematical Sciences, Research Institute of Nuclear Physics named after. D. V. Skobeltsyn Moscow State University. M. V. Lomonosova
“Science and Life” No. 10, 2008
Almost a hundred years have passed since cosmic rays were discovered - streams of charged particles coming from the depths of the Universe. Since then, many discoveries have been made related to cosmic radiation, but many mysteries still remain. One of them is perhaps the most intriguing: where do particles with an energy of more than 10 20 eV come from, that is, almost a billion trillion electron volts, a million times greater than what will be obtained in the most powerful accelerator - the Large Hadron Collider? What forces and fields accelerate particles to such monstrous energies?
Cosmic rays were discovered in 1912 by the Austrian physicist Victor Hess. He was an employee of the Radium Institute in Vienna and conducted research on ionized gases. By that time, they already knew that all gases (including the atmosphere) are always slightly ionized, which indicated the presence of a radioactive substance (like radium) either in the gas or near a device measuring ionization, most likely in the earth's crust. Experiments with lifting an ionization detector in a balloon were conceived to test this assumption, since gas ionization should decrease with distance from the earth's surface. The answer was the opposite: Hess discovered some radiation, the intensity of which increased with altitude. This suggested the idea that it comes from space, but the extraterrestrial origin of the rays was finally proven only after numerous experiments (W. Hess was awarded the Nobel Prize only in 1936). Recall that the term “radiation” does not mean that these rays are purely electromagnetic in nature (like sunlight, radio waves or X-rays); it was used to discover a phenomenon whose nature was not yet known. And although it soon became clear that the main component of cosmic rays is accelerated charged particles, protons, the term was retained. The study of the new phenomenon quickly began to produce results that are usually considered to be “the cutting edge of science.”
The discovery of very high-energy cosmic particles immediately (long before the proton accelerator was created) raised the question: what is the mechanism for accelerating charged particles in astrophysical objects? Today we know that the answer turned out to be non-trivial: a natural, “cosmic” accelerator is radically different from man-made accelerators.
It soon became clear that cosmic protons, flying through matter, interact with the nuclei of its atoms, giving birth to previously unknown unstable elementary particles (they were observed primarily in the Earth’s atmosphere). The study of the mechanism of their birth has opened a fruitful path for constructing a taxonomy of elementary particles. In the laboratory, they learned to accelerate protons and electrons and produce huge flows of them, incomparably denser than in cosmic rays. Ultimately, it was experiments on the interaction of particles that received energy in accelerators that led to the creation of a modern picture of the microworld.
In 1938, French physicist Pierre Auger discovered a remarkable phenomenon - showers of secondary cosmic particles that arise as a result of the interaction of primary protons and nuclei of extremely high energies with the nuclei of atmospheric atoms. It turned out that in the spectrum of cosmic rays there are particles with an energy of the order of 10 15 –10 18 eV - millions of times more than the energy of particles accelerated in the laboratory. Academician Dmitry Vladimirovich Skobeltsyn attached particular importance to the study of such particles and immediately after the war, in 1947, together with his closest colleagues G. T. Zatsepin and N. A. Dobrotin, organized comprehensive studies of cascades of secondary particles in the atmosphere, called extensive air showers (EAS) . The history of the first studies of cosmic rays can be found in the books of N. Dobrotin and V. Rossi. Over time, the school of D.V. Skobeltsyna grew into one of the most powerful in the world and for many years determined the main directions in the study of ultra-high-energy cosmic rays. Her methods made it possible to expand the range of energies under study from 10 9 –10 13 eV, recorded on balloons and satellites, to 10 13 –10 20 eV. Two aspects made these studies particularly attractive.
Firstly, it became possible to use high-energy protons created by nature itself to study their interaction with the nuclei of atmospheric atoms and decipher the finest structure of elementary particles.
Secondly, it became possible to find objects in space capable of accelerating particles to extremely high energies.
The first aspect turned out to be not as fruitful as hoped: studying the fine structure of elementary particles required much more data on the interaction of protons than cosmic rays can provide. At the same time, an important contribution to ideas about the microworld was made by studying the dependence of the most general characteristics of the interaction of protons on their energy. It was during the study of EASs that a feature was discovered in the dependence of the number of secondary particles and their energy distribution on the energy of the primary particle, associated with the quark-gluon structure of elementary particles. These data were later confirmed in experiments at accelerators.
Today, reliable models of the interaction of cosmic rays with the nuclei of atmospheric atoms have been constructed, which have made it possible to study the energy spectrum and composition of their primary particles of the highest energies. It became clear that cosmic rays play no less a role in the dynamics of the Galaxy’s development than its fields and flows of interstellar gas: the specific energy of cosmic rays, gas and magnetic field is approximately equal to 1 eV per cm 3. With such a balance of energy in the interstellar medium, it is natural to assume that the acceleration of cosmic ray particles most likely occurs in the same objects that are responsible for heating and releasing gas, for example, in novae and supernovae during their explosion.
The first mechanism of cosmic ray acceleration was proposed by Enrico Fermi for protons chaotically colliding with magnetized clouds of interstellar plasma, but could not explain all the experimental data. In 1977, Academician Hermogenes Filippovich Krymsky showed that this mechanism should accelerate particles in supernova remnants much more strongly at the fronts of shock waves, the speeds of which are orders of magnitude higher than the speeds of clouds. Today it has been reliably shown that the mechanism of acceleration of cosmic protons and nuclei by a shock wave in the shells of Supernovae is most effective. But it is unlikely to be able to reproduce it in laboratory conditions: acceleration occurs relatively slowly and requires enormous amounts of energy to retain accelerated particles. In supernova shells, these conditions exist due to the very nature of the explosion. It is remarkable that the acceleration of cosmic rays occurs in a unique astrophysical object, which is responsible for the synthesis of heavy nuclei (heavier than helium) actually present in cosmic rays.
In our Galaxy, there are several known Supernovae less than a thousand years old that have been observed with the naked eye. The most famous are the Crab Nebula in the constellation Taurus (“The Crab” is the remnant of the Supernova explosion in 1054, noted in the eastern chronicles), Cassiopeia-A (observed in 1572 by the astronomer Tycho Brahe) and the Kepler Supernova in the constellation Ophiuchus (1680). The diameters of their shells today are 5–10 light years (1 light year = 10 16 m), that is, they are expanding at a speed of the order of 0.01 the speed of light and are located at distances of approximately ten thousand light years from the Earth. The shells of Supernovae (“nebulae”) were observed in the optical, radio, X-ray and gamma-ray ranges by the Chandra, Hubble and Spitzer space observatories. They reliably showed that acceleration of electrons and protons, accompanied by X-ray radiation, actually occurs in the shells.
About 60 supernova remnants younger than 2000 years could fill interstellar space with cosmic rays with a measured specific energy (~1 eV per cm 3), while less than ten of them are known. This shortage is explained by the fact that in the plane of the Galaxy, where stars and supernovae are concentrated, there is a lot of dust, which does not transmit light to the observer on Earth. Observations in X-ray and gamma rays, for which the dust layer is transparent, have made it possible to expand the list of observed “young” supernova shells. The most recent of these newly discovered shells was Supernova G1.9+0.3, observed with the Chandra X-ray telescope beginning in January 2008. Estimates of the size and expansion rate of its shell indicate that it flared up approximately 140 years ago, but was not visible in the optical range due to the complete absorption of its light by the dust layer of the Galaxy.
The data on Supernovae exploding in our Milky Way Galaxy is supplemented by much richer statistics on Supernovae in other galaxies. Direct confirmation of the presence of accelerated protons and nuclei is gamma radiation with high energy photons resulting from the decay of neutral pions - products of the interaction of protons (and nuclei) with the source matter. Such high-energy photons are observed using telescopes that detect the Vavilov-Cherenkov glow emitted by secondary EAS particles. The most advanced instrument of this type is a six-telescope array created in collaboration with HESS in Namibia. The Crab's gamma rays were the first to be measured, and its intensity became the measure of intensity for other sources.
The obtained result not only confirms the presence of a mechanism for the acceleration of protons and nuclei in a Supernova, but also allows us to estimate the spectrum of accelerated particles: the spectra of “secondary” gamma rays and “primary” protons and nuclei are very close. The magnetic field in the Crab and its size allow the acceleration of protons to energies of the order of 10 15 eV. The spectra of cosmic ray particles in the source and in the interstellar medium are somewhat different, since the probability of particles leaving the source and the lifetime of particles in the Galaxy depend on the energy and charge of the particle. Comparing the energy spectrum and composition of cosmic rays measured near Earth with the spectrum and composition at the source made it possible to understand how long particles travel among stars. There were significantly more lithium, beryllium and boron nuclei in cosmic rays near the Earth than in the source - their additional number appears as a result of the interaction of heavier nuclei with interstellar gas. By measuring this difference, we calculated the amount X the substance through which cosmic rays passed while wandering in the interstellar medium. In nuclear physics, the amount of matter that a particle encounters on its path is measured in g/cm2. This is due to the fact that in order to calculate the reduction in the flux of particles in collisions with nuclei of matter, it is necessary to know the number of collisions of a particle with nuclei that have different areas (sections) transverse to the direction of the particle. By expressing the amount of matter in these units, a single scale of measurement is obtained for all nuclei.
Experimentally found value X~ 5–10 g/cm2 allows you to estimate the lifetime t cosmic rays in the interstellar medium: t ≈ X/ρ c, Where c- particle speed approximately equal to the speed of light, ρ ~10 –24 g/cm 3 - average density of the interstellar medium. Hence the lifetime of cosmic rays is about 10 8 years. This time is much longer than the time of flight of a particle moving at a speed With in a straight line from the source to the Earth (3·10 4 years for the most distant sources on the side of the Galaxy opposite us). This means that the particles do not move in a straight line, but experience scattering. Chaotic magnetic fields of galaxies with induction B ~ 10 –6 gauss (10 –10 tesla) move them around a circle with a radius (gyroradius) R = E/3 × 10 4 B, where R in m, E- particle energy in eV, V - magnetic field induction in gauss. At moderate particle energies E
Approximately in a straight line, only particles with energy will come from the source E> 10 19 eV. Therefore, the direction of EAS-producing particles with energies less than 10 19 eV does not indicate their source. In this energy region, all that remains is to observe the secondary radiation generated in the sources themselves by protons and cosmic ray nuclei. In the observable energy region of gamma radiation ( E
The idea of cosmic rays as a “local” galactic phenomenon turned out to be true only for particles of moderate energies E
In 1958, Georgiy Borisovich Christiansen and German Viktorovich Kulikov discovered a sharp change in the appearance of the energy spectrum of cosmic rays at an energy of the order of 3·10 15 eV. At energies below this value, experimental data on the spectrum of particles were usually presented in a “power-law” form so that the number of particles N with a given energy E was considered inversely proportional to the energy of the particle to the power γ: N(E) = a/Eγ (γ is the differential spectrum indicator). Up to an energy of 3·10 15 eV, the indicator γ = 2.7, but upon transition to higher energies the energy spectrum experiences a “break”: for energies E> 3·10 15 eV γ becomes 3.15. It is natural to associate this change in the spectrum with the approach of the energy of accelerated particles to the maximum possible value calculated for the acceleration mechanism in Supernovae. This explanation of the break in the spectrum is also supported by the nuclear composition of primary particles in the energy range 10 15 –10 17 eV. The most reliable information about it is provided by complex EAS installations - “MGU”, “Tunka”, “Tibet”, “Cascade”. With their help, one obtains not only information about the energy of primary nuclei, but also parameters depending on their atomic numbers - the “width” of the shower, the ratio between the number of electrons and muons, between the number of the most energetic electrons and their total number. All these data indicate that with an increase in the energy of primary particles from the left boundary of the spectrum before its break to the energy after the break, their average mass increases. This change in the mass composition of particles is consistent with the model of particle acceleration in Supernovae - it is limited by the maximum energy, which depends on the charge of the particle. For protons, this maximum energy is of the order of 3·10 15 eV and increases in proportion to the charge of the accelerated particle (nucleus), so that iron nuclei are effectively accelerated up to ~10 17 eV. The intensity of particle flows with energy exceeding the maximum decreases rapidly.
But the registration of particles with even higher energies (~3·10 18 eV) showed that the spectrum of cosmic rays not only does not break, but returns to the form observed before the break!
Measurements of the energy spectrum in the “ultra-high” energy region ( E> 10 18 eV) are very difficult due to the small number of such particles. To observe these rare events, it is necessary to create a network of detectors for the flow of EAS particles and the Vavilov-Cherenkov radiation and ionization radiation (atmospheric fluorescence) generated by them in the atmosphere over an area of hundreds and even thousands of square kilometers. For such large, complex installations, locations are chosen with limited economic activity, but with the ability to ensure reliable operation of a huge number of detectors. Such installations were built first on areas of tens of square kilometers (Yakutsk, Havera Park, Akeno), then hundreds (AGASA, Fly's Eye, HiRes), and finally, installations of thousands of square kilometers are now being created (Pierre Auger Observatory in Argentina, Telescopic installation in Utah, USA).
The next step in the study of ultra-high-energy cosmic rays will be the development of a method for detecting EASs by observing atmospheric fluorescence from space. In cooperation with several countries, Russia is creating the first space EAS detector, the TUS project. Another such detector is expected to be installed on the International Space Station ISS (JEM-EUSO and KLPVE projects).
What do we know today about ultra-high energy cosmic rays? The lower figure shows the energy spectrum of cosmic rays with energies above 10 18 eV, which were obtained using the latest generation installations (HiRes, Pierre Auger Observatory) together with data on cosmic rays of lower energies, which, as shown above, belong to the Milky Way Galaxy. It can be seen that at energies 3·10 18 –3·10 19 eV the differential energy spectrum index decreased to a value of 2.7–2.8, exactly the same as that observed for galactic cosmic rays, when particle energies are much less than the maximum possible for galactic accelerators . Does this not indicate that at ultra-high energies the main flow of particles is created by accelerators of extragalactic origin with a maximum energy significantly higher than the galactic one? The break in the spectrum of galactic cosmic rays shows that the contribution of extragalactic cosmic rays changes sharply upon transition from the region of moderate energies 10 14 –10 16 eV, where it is approximately 30 times less than the contribution of galactic ones (the spectrum indicated by the dotted line in the figure), to the region of ultra-high energies where it becomes dominant.
In recent decades, numerous astronomical data have been accumulated on extragalactic objects capable of accelerating charged particles to energies much higher than 10 19 eV. An obvious sign that an object of size D can accelerate particles to energy E, is the presence along the entire length of this object of a magnetic field B such that the gyroradius of the particle is less D. Such candidate sources include radio galaxies (emitting strong radio emissions); nuclei of active galaxies containing black holes; colliding galaxies. All of them contain jets of gas (plasma) moving at enormous speeds, approaching the speed of light. Such jets play the role of shock waves necessary for the operation of the accelerator. To estimate their contribution to the observed intensity of cosmic rays, it is necessary to take into account the distribution of sources over distances from the Earth and the energy losses of particles in intergalactic space. Before the discovery of background cosmic radio emission, intergalactic space seemed “empty” and transparent not only to electromagnetic radiation, but also to ultra-high energy particles. The density of gas in intergalactic space, according to astronomical data, is so small (10 –29 g/cm 3) that even at enormous distances of hundreds of billions of light years (10 24 m) particles do not encounter the nuclei of gas atoms. However, when it turned out that the Universe is filled with low-energy photons (approximately 500 photons/cm 3 with energy E f ~10 –3 eV), remaining after the Big Bang, it became clear that protons and nuclei with energy greater E~5·10 19 eV, the Greisen-Zatsepin-Kuzmin (GZK) limit, must interact with photons and lose b O most of your energy. Thus, the overwhelming part of the Universe, located at distances of more than 10 7 light years from us, turned out to be inaccessible for observation in rays with an energy of more than 5·10 19 eV. Recent experimental data on the spectrum of ultra-high energy cosmic rays (HiRes installation, Pierre Auger Observatory) confirm the existence of this energy limit for particles observed from Earth.
As can be seen, it is extremely difficult to study the origin of ultra-high-energy cosmic rays: the majority of possible sources of cosmic rays of the highest energies (above the GZK limit) are so far away that the particles lose the energy acquired at the source on their way to Earth. And at energies less than the GZK limit, the deflection of particles by the magnetic field of the Galaxy is still large, and the direction of arrival of particles is unlikely to be able to indicate the position of the source on the celestial sphere.
In the search for sources of ultra-high energy cosmic rays, an analysis of the correlation of the experimentally measured direction of arrival of particles with sufficiently high energies is used - such that the fields of the Galaxy slightly deflect the particles from the direction towards the source. Previous generation installations have not yet provided convincing data on the correlation of the direction of arrival of particles with the coordinates of any specially selected class of astrophysical objects. The latest data from the Pierre Auger Observatory can be considered as a hope for obtaining data in the coming years on the role of AGN-type sources in the creation of intense particle flows with energies on the order of the GZK limit.
Interestingly, the AGASA installation received indications of the existence of “empty” directions (those where there are no known sources), along which two or even three particles arrive during the observation. This aroused great interest among physicists involved in cosmology - the science of the origin and development of the Universe, inextricably linked with the physics of elementary particles. It turns out that some models of the structure of the microcosm and the development of the Universe (Big Bang theory) predict the preservation in the modern Universe of supermassive elementary particles with a mass of the order of 10 23 -10 24 eV, of which matter should consist at the earliest stage of the Big Bang. Their distribution in the Universe is not very clear: they can either be uniformly distributed in space, or “attracted” to massive regions of the Universe. Their main feature is that these particles are unstable and can decay into lighter ones, including stable protons, photons and neutrinos, which acquire enormous kinetic energies - more than 10 20 eV. Places where such particles are preserved (topological defects of the Universe) may turn out to be sources of protons, photons or ultra-high energy neutrinos.
As in the case of galactic sources, the existence of extragalactic ultra-high-energy cosmic ray accelerators is confirmed by data from gamma-ray detectors, for example, the HESS telescopes, aimed at the above extragalactic objects - candidate sources of cosmic rays.
Among them, the most promising were active galactic nuclei (AGNs) with gas jets. One of the most well-studied objects at the HESS installation is the M87 galaxy in the constellation Virgo, at a distance of 50 million light years from our Galaxy. At its center there is a black hole, which provides energy to the processes near it and, in particular, to the giant jet of plasma belonging to this galaxy. The acceleration of cosmic rays in M87 is directly confirmed by observations of its gamma radiation, the energy spectrum of photons with an energy of 1–10 TeV (10 12 –10 13 eV), observed at the HESS installation. The observed gamma-ray intensity from M87 is approximately 3% of the intensity of the Crab. Taking into account the difference in distance to these objects (5000 times), this means that the luminosity of M87 exceeds the luminosity of the Crab by 25 million times!
Particle acceleration models generated for this object indicate that the intensity of particles accelerated in M87 could be so great that even at a distance of 50 million light years, the contribution from this source could produce the observed intensity of cosmic rays with energies above 10 19 eV.
But here’s a mystery: in modern data on EASs towards this source there is no excess of particles with an energy of the order of 10 19 eV. But won't this source appear in the results of future space experiments, at such energies when distant sources no longer contribute to the observed events? The situation with a break in the energy spectrum can be repeated again, for example at an energy of 2·10 20 . But this time the source should be visible in measurements of the direction of the primary particle's trajectory, since energies > 2·10 20 eV are so high that the particles should not be deflected in galactic magnetic fields.
As we see, after a century of studying cosmic rays, we are again waiting for new discoveries, this time ultra-high energy cosmic radiation, the nature of which is still unknown, but can play an important role in the structure of the Universe.
Literature:
1) Dobrotin N.A. Cosmic rays. - M.: Publishing house. USSR Academy of Sciences, 1963.
2) Murzin V.S. Introduction to Cosmic Ray Physics. - M.: Publishing house. Moscow State University, 1988.
3) Panasyuk M. I. Strangers of the Universe, or Echoes of the Big Bang. - Fryazino: “Vek2”, 2005.
4) Rossi B. Cosmic rays. - M.: Atomizdat, 1966.
5) Khrenov B.A. Relativistic meteors// Science in Russia, 2001, No. 4.
6) Khrenov B.A. and Panasyuk M.I. Messengers of space: far or near?// Nature, 2006, No. 2.
7) Khrenov B.A. and Klimov P.A. Opening expected// Nature, 2008, No. 4.
