cosmic rayAlso known ascosmic rays, is fromthe outer spaceCharged high energySubatomic particle。They may produce secondary particles that penetrate the earth's atmosphere and surface.radialThe term comes from the history of electromagnetic radiation.The main primary cosmic rays (particles from deep space impacting the atmosphere) are generally stable particles on the earth, such as protons, atomic nuclei, or electrons.However, there are very few stable proportionsAntimatterParticles, likepositronorAntiprotonThe remaining small part is an active field of research.
About 89% of cosmic rays are pureproton, 10% isheliumNuclear (i.eAlpha particle）And 1% are heavy elements.These nuclei make up 99% of cosmic rays.aloneElectronics(likeBeta particle, although the source is still unclear), constituting the majority of the remaining 1%;Gamma rayAnd ultrahigh energyneutrinoOnly a tiny part.
The variety of particle energy shows that cosmic rays have a wide range of sources.The source of these particles may besunlight(or other stars) or from distant visibleuniverse, produced by some unknown physical mechanisms.The energy of cosmic rays can exceed 10twentyeV, far more than on earthParticle acceleratorAttainable 10twelveTo 10thirteeneV，Make many peopleCosmic rays with greater energyInterested in research.[1]
Viacosmic rayNucleosynthesisCosmic rays play a major role in the production of lithium, beryllium, and boron in the universe.They also produce someradio isotope, likeCarbon-14。stayParticle physicsIn the history ofMuonandPion。Cosmic rays also cause most of theBackground radiationBecause the cosmic rays outside the earth's atmosphere and in the magnetic field are very strong, they have a significant impact on the design of maintaining the safety of astronauts on spacecraft navigating in interplanetary space.[2-3]
A. H. Becquerel Discovered in 1896radioactivityLater, many people believed that the current in the atmosphere (ionization）Radiation only from radioactive substances in the soil or produced radioactive gases (isotopes of radon).From 1900 to 1910, the measurement of ionization rate with increasing height in a decade showed a decrease that could be explained by the absorption of ionizing radiation by air.later,Victor Hess In 1912, we used aHot Air Balloon, with threeelectrometer, climbed 5300 meters high.He detected that the ionization rate had increased to about four times the ground rate.He concluded that "the best explanation for my observation is to imagine a high penetration ray entering the atmosphere from above."Victor Hess Because this discovery named "cosmic rays" by later generations was obtained in 1936The nobel prize in physics。
cosmic rays
Cosmic rays can be roughly divided into two categories: primary and derived cosmic rays.Cosmic rays generated by astrophysics outside the solar system are protocosmic rays;These protocosmic rays will interact withInterstellar matterThe action produces derivative (secondary) cosmic rays.The sun is generatingFlash flameSome low-energy cosmic rays will also be generated.stayEarth's atmosphereThe exact composition of the outer protocosmic rays depends on the observationEnergy spectrumWhich parts of.However, in general, almost 90% of the incoming cosmic rays areproton, 9% isheliumNuclear（Alpha particle）, and about 1% areElectronics。The proportion of hydrogen and helium nuclei (28% of the mass of helium nuclei) is about the same as that of these elements in the universeElement abundance(24% by mass of helium).
The rest is rich in other heavy atomic nuclei from the final product of stellar nuclear synthesis.Derived cosmic rays contain other atomic nuclei, which are not rich in nuclear synthesis orbig bangPrimarylithium、beryllium, andboron。The proportion of these lighter nuclei appearing in cosmic rays is far greater than that in the solar atmosphere (1:100 particles), and their abundance is abouthelium10 of.
This difference in abundance is the result of derived cosmic rays.When the heavy nuclear components of cosmic rays, namely carbon and oxygen nuclei, collide with interstellar matter, they split into lighter lithium, beryllium and boron nuclei (this process is calledCosmic ray spallation）。The energy spectrum of lithium, beryllium and boron found is more narrow than that from carbon or oxygen, which indicates that there are a fewCosmic ray spallationIt is produced by higher energy atomic nuclei, presumably because they are derived fromGalacticThe magnetic field escapes.Spallation also affects thescandium、titanium, vanadium andmanganeseIonsThe abundance of equality is responsible. They are in the cosmic rayironAnd nickel nucleiInterstellar matterImpact (seeNatural background radiation）。
Even if satellite experiments found someAntiprotonandpositronThere is evidence of existence, but there is no evidence of the existence of complex antimatter nuclei (such as anti helium nuclei).The antimatter abundances observed in the primordial cosmic rays are consistent with the theory that they can also be generated by the primordial cosmic rays hitting ordinary matter in deep space and in the process of deriving cosmic rays.For example, a standard method for producing antiprotons in the laboratory is to hit other protons with protons with energy greater than 6GeV, while it is easy for many protons in the original cosmic ray to exceed this value.Whether in the Milky Way or not, when simple antimatter can be generated by this process (not in the upper atmosphere), they may still travel a long distance to reach the Earth, rather than being annihilated by collision with other hydrogen atoms in interstellar space.The antiprotons arriving at the Earth are characterized by only 2GeV energy at most, which shows that their production process is basically different from that of protons in cosmic rays.
In the past, people believed that thefluxIt has been quite stable over time.Recent research shows that, on a time scale of 1.5 to 2000 years, there is evidence that the flux of cosmic rays has changed in the past 40000 years.[4]
Radiographic findings
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In 1912, German scientist Viktor Hans tookionizationRoom in balloon lift off measurementAir ionizationIn the experiment, it is found that the current in the ionization chamber increases with the elevation, so it is believed that the current is a highly penetrating current from outside the earthradialSo someone named it "cosmic ray".
Cosmic rays, also called cosmic rays, come fromthe outer spaceCharged high energySubatomic particle。They may produceSecondary particlePenetrate the earth's atmosphere and surface.radialThe term comes from the history of electromagnetic radiation.majorPrimary cosmic ray(Particles from deep space impacting the atmosphere) Components are generally stable particles on the earth, such as protons, atomic nuclei, or electrons.However, there are very few stable proportionsAntimatterParticles, likepositronorAntiprotonThe remaining small part is an active field of research.
About 89% of cosmic rays are pureprotonOr hydrogen nuclei, 10%Helium nuclei orAlpha particleAnd 1%Heavy element。These nuclei make up 99% of cosmic rays.Lonely electrons (likeBeta particle, although the source is still unclear), constituting the majority of the remaining 1%;Gamma rayAnd ultrahigh energyneutrinoOnly a tiny part.
The variety of particle energy shows that cosmic rays have a wide range of sources.These particles can originate from the sun (or other stars)
cosmic rays
Some programs come from the distant visible universe and are generated by some unknown physical mechanisms.The energy of cosmic ray can exceed 10E20eV, far more than on earthParticle acceleratorThe achievable 10E12 to 10E13 eV makes many peopleCosmic rays with greater energyInterested in research[1]。
Viacosmic rayNucleosynthesisCosmic rays play a major role in the production of lithium, beryllium, and boron in the universe.They also produce someradio isotope, likeCarbon-14。In the history of particle physicspositron, μ andPion。Cosmic rays also cause most of theBackground radiationBecause the cosmic rays outside the earth's atmosphere and in the magnetic field are very strong, they have a significant impact on the design of maintaining the safety of astronauts on spacecraft navigating in interplanetary space.
Cosmic rays can be roughly divided into two categories: primary and derived cosmic rays.Cosmic rays generated by astrophysics outside the solar system are protocosmic rays;These protocosmic rays will interact withInterstellar matterThe action produces derivative (secondary) cosmic rays.The sun is generatingFlash flameSome low-energy cosmic rays will also be generated.stayEarth's atmosphereThe exact composition of the outer protocosmic rays depends on the observationEnergy spectrumWhich parts of the.However, in general, almost 90% of the incoming cosmic rays areproton, 9% isheliumNuclear（Alpha particle）, and about 1% are electrons.The proportion of hydrogen and helium nuclei (28% of the mass of helium nuclei) is about the same as that of these elements in the universeElement abundance(24% by mass of helium).
cosmic rays
On October 14, 2022, based on the observation data collected in the first six years, the "Wukong" international cooperation group obtained the accurate measurement results of B/C and B/O in the energy band from 10 GeV/n to 5.6 TeV/n (figure).This is the first time in the world to achieve accurate measurement of B/C and B/O above 1 TeV/n, and the upper energy limit is five times higher than that of the Alpha Magnetic Spectrometer (AMS-02) experiment.The detection results of Wukong show that B/C and B/O obviously deviate from the behavior characteristics of a single power law distribution in a wide energy range.[7]
On February 26, 2024, the Institute of High Energy Physics of the Chinese Academy of Sciences announced that Chinese researchers found a giant ultra-high energy gamma ray bubble structure in the Cygnus star forming region through the High Altitude Cosmic Ray Observatory (LHAASO, "Lasso") in Daocheng, Sichuan, and for the first time internationally certified the origin of cosmic rays with energy higher than 100 million electron volts.This achievement was published in the academic journal Science Bulletin in the form of a cover article on February 26, Beijing time.[9]
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Solar modulation refers to the process in which the sun or solar wind changes the intensity and energy spectrum of cosmic rays from the Milky Way entering the solar system.When the sun is active, the cosmic rays in the Milky Way will enter the solar system less than in the quiet period.For this reason, the cosmic rays in the Milky Way follow the same 11 year cycle as the sun, but the difference is that intense solar activity corresponds to low cosmic rays (entering the solar system), and vice versa.
Early Earth Impact
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About 4.6 billion years ago, the Earth just moved fromSolar nebulaFormed in.The nascent earth has solid matter gathered into its core and a large amount of solid matter around ithydrogen、heliumGas, calledFirst generation atmosphere。
cosmic rays
At that time, becauseEarth massIt is not big enough. It lacks enough gravity to absorb the atmospheresolar wind(The sun is constantly thrown out due to the expansion of high temperatureParticle FlowThe speed near the sun is about 350~450 kilometers per second), so the first generation atmosphere dominated by hydrogen and helium will soon be blown into space.During the continuous rotation and accumulation of the earth, due to its own condensation and contraction and the disintegration of internal radioactive materials (such as uranium, thorium, etc.),Primitive EarthThe temperature increases continuously, and the interior even reaches the level of incandescence.Then the heavy matter sinks into the interior, formingearth 's coreandmantleThe lighter material is distributed on the surface, forming the crust.
The newly formed crust is relatively weak, and the temperature inside the earth is very high, sovolcanoWith frequent activities, many gases from volcanoes form the second generation atmosphere, namelyPrimitive atmosphere。
The original atmosphere is a reducing atmosphere without free oxygen, mostly in the form of compounds, with larger molecular weight and slower movement. At this time, the mass and gravity of the earth are enough to absorb the atmosphere, so the various components of the original atmosphere are not easy to escape.Later, the temperature of the earth's surface gradually decreased,Water vaporWhen it condenses into rain and falls to a low place on the earth's surface, it becomes a river, a lake and a primitive ocean.At that time, there was no free oxygen (O2) in the atmosphere, so there was no oxygen in high altitudeozone(O3) layer to block and absorbsolar radiationTherefore, the ultraviolet ray can reach the surface of the earth directly and become the energy source for the synthesis of organic matter.In addition, sky dischargeVolcano eruptionHeat releasedcosmic rays(From spaceHigh-energy particleStream, whose source is not known yet) and meteorite passing throughatmosphereThe shock wave (which can produce a high temperature of several thousand to tens of thousands of degrees Celsius) and so on, also contribute to the synthesis of organic compounds.But the sky discharge is probably the most important, because this kind of energy provides more energy and is released near the ocean surface, where it acts onReducibilityOrganic compounds synthesized in the atmosphere are easy to be washedPrimitive oceanin
Historical origin
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The origin of cosmic rays usually refers to the main components of cosmic rays - variousNucleusThe process of launching and accelerating.The movement and distribution of cosmic rays in space belong to the propagation of cosmic rays.The origin and propagation of cosmic rays are closely related to each other: the stages of acceleration and propagation cannot be completely separated;Quite a partPrimary cosmic rayNuclei arise in the process of propagation.
The origin and propagation of cosmic rays areHigh-energy astrophysicsOne of the most important issues.Cosmic rays are variousCelestial evolutionThe products of these processes, especially the products of various high-energy astrophysical processes, carry rich information about these processes.
However, there are many difficulties in the research of the origin and propagation of cosmic rays: first, because the charged particles of cosmic raysinterstellarIn the process of space propagationmagnetic fieldIt is impossible to directly detect their distribution in space due to the deflection of cosmic rays. Their existence can only be inferred indirectly from the radio waves, X-rays and gamma rays emitted by cosmic rays in the process of motion and action.During the propagation of cosmic raysInterstellar matterFunction, constantly changing its energy and composition. The observed primary cosmic ray composition and energy spectrum are jointly determined by the original origin and propagation process.It is necessary to consider the role of cosmic rays in the propagation process with interstellar matter and the modulation of the magnetic field of the Earth and the solar system when inferring from the primary cosmic rays near the Earth that generated the original cosmic rays at the sourceradio, X-ray and gamma ray observations to infer the distribution of cosmic ray particles in the Milky Way, we must also understandInterstellar mediumDistribution of;However, people's understanding of the solar system's magnetic field and some important interstellar media (such as interstellar hydrogen molecules) is just beginning.In addition, with the progress of primary cosmic ray observation, existing nuclear physics andHigh-energy physicsKnowledge (e.g. nuclear reactionssection、Long-lived radionuclideThe lack of decay lifetime and branching ratio has increasingly become an important reason for limiting people's understanding of primitive cosmic rays.
cosmic rayHigh-energy particleIt should originate from various high-energy celestial bodies or celestial high-energy processes.Sun and othersfixed starHigh energy activity on the surface, supernova explosionPulsar, quasars andActive galaxyAll of them may be cosmic ray sources.At present, it is generally believed that most cosmic ray particles originated in the Milky Way.Solar flareHigh energy processes such as explosion are accompanied by the emission of particles, but thissolar activityIt can only produce a small part of cosmic ray particles in the space of the solar system, and the average energy of solar particles is only tens of trillionElectron voltMost cosmic rays should come from outside the solar system.The particle emission of ordinary stars in the Milky Way can only produce a negligible part of the cosmic ray particles in the Milky Way, and most cosmic rays should be generated from more than ordinary starsStellar activityMore intense process.
Supernova explosion is the most violent high-energy phenomenon in the Milky Way.The average energy output of the galactic supernova explosion can meet the maintenance requirementsGalactic cosmic rayThe need for energy density.Crab NebulaIntense emission height of supernova remnantspolarizationNon thermalradioRadiation, they should be the synchrotron radiation of high-energy electrons in the magnetic field.Supernova remnantThere are a large number of high-energy electrons in, which should be the birthplace of high-energy electrons in cosmic rays.It is generally assumed that supernova explosions and their remnants should also emit high-energy atomic nuclei, becoming the main source of cosmic rays.Hydrogen and helium nuclei in cosmic raysRelative abundanceIt is smaller than the average abundance of the solar system or the Milky Way, indicating that the cosmic ray nuclei may come fromStellar evolutionLate stage of the process.Heavy elements in cosmic rays (such asZ>60) More, they may be fast under the condition of supernova explosionneutronThe product of the capture process (gamma process).There are many neutron rich isotopes of some elements in cosmic rays, which also indicates that cosmic rays may originate from the neutron rich environment formed by supernova explosion.However, so far there is no direct evidence that supernovae and their remnants emit high-energy nuclei.How the energy released by the supernova explosion is converted into the kinetic energy of particles, and how the cosmic ray particles can be formed from many discrete sources such as supernovaePower lawEnergy spectrum is the difficulty of supernova origin model.For primary cosmic raysElement abundanceThe analysis of the recent measurement results of, shows that the distribution of the relative abundances of the heavy elements of the primitive cosmic rays is close to that of the solar system, which is very different from the expected distribution of the gamma process, and is also inconsistent with the supernova origin model.
E. FermiIn 1949, he proposed the mechanism of statistical acceleration of cosmic rays in interstellar media: charged particles are accelerated in constant collisions with randomly moving magnetic fields.Fermi accelerationThe mechanism can explain the power law spectrum of cosmic rays.However, the Fermi mechanism requires that the particles have another initial acceleration process and that there is enough energy to supply the motion of the magnetic field in the interstellar medium;At the same time, Fermi mechanism is not conducive to speeding up heavyatomNuclear, difficult to interpret observed cosmic raysabundanceDistribution.Recent X-ray observations have found that,Supernova remnantAt least in 104 yearsshock wave。Theoretical analysis shows that shock waves in interstellar media can effectively accelerate cosmic ray particles and generatePower lawEnergy spectrum.The strong shock wave caused by high-energy activities such as supernova explosion may travel long enough in the hot and thin gas in interstellar space, so that the shock wave acceleration mechanism may effectively accelerate cosmic ray particles.However, the recent discovery of primitive cosmic raysElement abundanceDistribution and AtomFirst ionization energyClosely related: the lower the first ionization energy of the element, the greater the ratio of the primitive cosmic ray abundance to the solar abundance.Therefore, the temperature of the origin and acceleration region of cosmic rays cannot be too high (<104 Kelvin), which makes it difficult for the supernova explosion and the acceleration mechanism in the high-temperature gas.X-ray astronomical observations have found that although a large number of late stars (K-type and M-type dwarfs) in the Milky Way have weak light radiation, the high-energy process of X-ray emission and flare activity (thus particle emission) is still very active, which may be an important birthplace of cosmic rays.But how to further accelerate the particles they emit is also an unsolved problem.The high-energy cosmic ray particles generated in the Milky Way should fly out of the Milky Way in 103~104 years if they propagate freely in space.According to the relative abundance of primary cosmic ray elements, the average material thickness through which cosmic ray particles pass is about 5 g/cm2, while the average density of interstellar gas in the silver disk is about 1hydrogen atom/Cm 3, the average residence time of cosmic rays in the silver disk is about 3 × 106 years, which is much longer than that of free particles passing through the silver disk.Therefore, cosmic ray particles in interstellar space do not propagate freely but diffuse in the non-uniform interstellar medium, and may be reflected at the boundary of the Milky Way Galaxy.The average lifetime of cosmic rays (107 years of liquid) deduced from the relative abundance of some long-lived isotopes (such as 10Be) in primary cosmic rays is longer than the retention time in the silver disk, soGalactic cosmic rayFor most of its lifetime, particles may propagate in the cosmic ray halo, a region of thin material around the silver disk.At present, people's knowledge about the Milky Way and their observation of cosmic rays are not enough to form and judge a detailed propagation model of cosmic rays.When dealing with problems related to cosmic ray propagation effects (such as inferring the composition and energy spectrum of primitive cosmic rays from the composition and energy spectrum of primitive cosmic rays), some simplified steady-state propagation models, such as leaky box models, are often used.The Leakbox Model Assumes Cosmic Rays in the GalaxyParticle densityWithout changing with time and place, cosmic ray particles diffuse in the Milky Way and slowly leak out of the Milky Way with a certain probability through the boundary.Since the 1960s, with the progress of primary cosmic rays and radio, X-ray and gamma ray astronomical observations, people's understanding of the origin and propagation of cosmic rays has been deepening, but due to the complexity of the problem, no satisfactory model has been obtained so far.People know less about extremely high energy cosmic rays;Even for the composition of this part of cosmic rays, there is still no clear understanding.Galactic magnetic fieldCan't store particles with energy higher than 1018 electron volts, GalaxyEndogenesisPole ofHigh-energy particleIt should be highly anisotropic;However, the anisotropy of cosmic ray particles with energy higher than 1018 electron volts in the direction of particles is more than 10%, and more particles do not come from the center of the Milky Way, so the high-energy cosmic ray particles may originate outside the Milky Way.Because of theSpatial densityVery low, the extragalactic region must have a much stronger cosmic ray particle source than the Milky Way to explain the observed extremely high energy cosmic ray particle flow.
mode
As we know, cosmic rays are mainly composed ofproton、Helium nucleus、Iron coreetc.Naked nucleusConstituentHigh-energy particle flow；It also contains neutralgamma ray And can cross the earthNeutrino stream。They are in the intergalactic Milky Way andSolar magnetic fieldSome of them eventually cross the atmosphere to reach the Earth.There are three main observation methods used in the study of the microcosmic world of cosmic rays, namely:Space observation, ground observation, underground (or underwater) observation.
Observation station
In order to observe cosmic rays effectively and for a long time, many countries have established observation stations one after another.In 1943,Former Soviet UnionstayArmeniaEstablished theAlagaz Mountain Station；After the war, Japan established aChenganshan Observatory；In 1954, China established theYunnan Dongchuan Station。In 1990, China and Japan jointly establishedTibet Yangbajing Cosmic Ray Observatory。Almost all foreign high-energy cosmic rays, exceptneutrinoWhen passing through the atmosphere externally, it will collide with atomic nuclei such as oxygen and nitrogen in the atmosphere, and transformsecondary cosmic ray Particles, andUltrahigh energy cosmic rayThe secondary particles of will have enough energy to produce the next generation of particles. If this continues, it will produce a huge particle swarm;This phenomenon was introduced in 1938The AlpsFound by observation and named“Extensive atmospheric shower”。
Extensive research
In the process of extensive atmospheric shower, it is difficult for particles with energy lower than 10 to 14 electron volts to reach the low altitude below 3000 meters, but the ultrahigh energy particle swarm develops to a maximum at 4000 meters.Because of TibetYangbajingLocated at an altitude of 4300 meters, it is free of snow all the year round, flat and open, and has convenient conditions in terms of energy, transportation and life. Scientific researchers can carry out continuous observation here for years.YiyangbajingScintillatorFor example, when particles pass through the scintillator, they lose energy to make the scintillator fluoresce. This flash passes through photocathode conversion andPhotomultiplier tubeIt becomes aElectric pulse signal。This signal is sent to the electronic recording system through the cable, and recorded by the tape all year round.At the same time, we can imagine that if we install more scintillators per unit area, the density will be greater;The more ray particles received, the more accurate the recording will be.exceptScintillator detectorIn addition, the cosmic ray acquisition mode of Yangba Well Station: 80 square metersLatex roomAnd local shower detectors;Neutron telescope in neutron reactor;Test type 50 m2 RPC carpetdetector。
The transformationShowerProcess.Almost all but neutrinosHigh-energy cosmic raysWhen passing through the atmosphere, it will collide with atomic nuclei such as oxygen and nitrogen in the atmosphere and transform into secondary cosmic ray particles, and the secondary particles of ultrahigh energy cosmic rays will have enough energy to produce the next generation of particles. If this continues, the conversion level by level will produce a hugeParticle swarm。In 1938, French Ogier observed this phenomenon in the Alps and named it“Extensive atmospheric shower”。
influence factor
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Gas barrier
Although there will be atmosphere to block some radiation when cosmic rays reach the earth, the intensity of the ray flow is still very large, which is likely to have a certain impact on air traffic.For example, the control system and navigation system used in modern aircraft are quite sensitiveMicrocircuitform.Once attacked by charged particles at high altitude, it may become invalid, bringing considerable trouble and threat to the flight of aircraft.
Other scientists believe that global warming, which has been widely concerned by the international community for a long time, may also be directly related to cosmic rays.This view holds that the greenhouse effect may not be the only culprit of global warming, and cosmic rays may promote global warming by changing the way clouds form in the lower atmosphere.These scientists believe that the change of cosmic ray level may be the key to explain this difficult problem.They pointed out that due to theHigh-energy particleThe charged ions formed by bombarding electrons from atoms can cause condensation of water droplets, thus increasing the growth of clouds.In other words, when there are fewer cosmic rays, there will be fewer clouds, so the sun can directly heat the earth's surface.The observational data of the solar activity and its radioactive intensity in the past 20 years support this new view, that is, when the solar activity becomes more intense, the coverage of low-level clouds will decrease.This is because the low-energy charged particles (namely, the solar wind) emitted from the sun can deflect the cosmic rays. With the intensification of solar activity, the solar wind also increases, so that there are fewer cosmic rays reaching the earth, so there are fewer clouds formed.In addition, in the upper space, if the concentration of charged particles generated by cosmic rays is very high, these charged ions may collide with each other, and thus recombine into neutral particles.However, charged ions at low altitude are kept for a relatively long time, which is enough to cause a new cloud shape
In addition, several American scientists also believe that cosmic rays may be related to the extinction and emergence of biological species.They believe that the sudden increase of cosmic rays at a certain stage is likely to damage the earthozone layerAnd increase theradioactivity, leading to speciesvariationEven extinction.On the other hand, these rays may cause new species to mutate, thus producing a new generation.This theory also points out that some creatures living in caves, under the sea or below the surface are not extinct because they can escape most of the radiation.From this point of view, cosmic rays really deserve the name“Space missile”。
research meaning
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Humans still cannot tell exactly where cosmic rays are generated, but it is generally believed that they may come fromSupernovaOutbreak, from far awayActive galaxy；They brought the sun and earth to the earth for freespace environment Valuable information.Scientists hope to receive these rays to observe and study their origin and microscopic changes in the cosmological environment.
The study of cosmic rays has gradually become an important field of astrophysics. Many scientists are trying to solve the mystery of cosmic rays.But until now, people have not fully understood origin of the cosmic rays.It is generally believed that the generation of cosmic rays may be related to the supernova explosion.In this regard, some scientists believe that cosmic rays are generated at the time of supernova explosion, and the "dead" stars emit large energyCharged particle flow, shooting into space;Another theory is that cosmic rays come from the debris of supernovae after the explosion.
No matter what the final conclusion will be, scientists always devote great enthusiasm to the study of cosmic rays.About why we should study cosmic rays,Roger Clay In his book Cosmic Missiles, he made a brilliant explanation:
"The study of cosmic rays has becomeAstrophysicsImportant areas.Although the origin of cosmic rays has not yet been determined, it is generally believed that the study of cosmic rays can obtain a lot of information about the processes in most of the strange environments of the universe:Radio galaxy, quasars, and surrounding neutron stars andblack holeRotating by boiling of incoming materialAccretion diskKnowledge.Our understanding of these astrophysical objects is still very shallow. The main driving force of today's cosmic ray research is the desire to understand why nature can produce particles of such extraordinary energy on these celestial bodies. "
Due to the importance of cosmic ray research, countries all over the world have invested funds and equipment to carry out research on it.The former Soviet Union, Japan, China, the United States, France and other countries have successively established cosmic ray observation stations.Although the origin of cosmic rays is still uncertain, scientists still gradually understand the various characteristics of cosmic rays and their impact on the earth and human environment.
Research History
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In 1903,rutherford(Ernest Rutherford, 1871-1937) (left) and H.L. Cooke studied this problem.They found that if all radioactive sources were carefully removedElectroscopeAbout ten pairs of ions will be produced every second in every cubic centimeter.They use iron and lead to shield the electroscope completely, and the generation of ions can be reduced by almost three tenths.They put forward an idea in the paper, which may have a strong penetration, similar toGamma rayRadiation from the outside into the electroscope, thereby stimulating the secondary radioactivity.
In 1909, Wright, in order to find out the cause of this phenomenonOntarioRepeat the above experiment on the ice surface of Lake Ontario and find that the free number decreases slightly.
cosmic rays
1910, French Father Theodor WulfEiffelExperiments were carried out on the top of the tower to compare the residual ionization strength of the tower top and the ground. The result is that the tower top is about 64% of the ground, higher than the 10% he expected.He believes that there may be gamma sources in the upper atmosphere, or the absorption of gamma rays may be smaller than expected.
1910-1911, Alfred GockelSwitzerlandZurich asked the balloon to take the ionization chamber to a height of 4500 meters, and recorded the discharge rate at several different heights.His conclusion is: "The phenomenon that the radiation decreases with the increase of height... is even more significant than previously observed."
The radioactivity of this source is more penetrating than the radioactivity that people were familiar with at that time, so people proposed that this radioactivity may come from outside the earth - this is the first sign of cosmic rays.
Austriaphysical scientistHess(Victor Franz Hess, 1883-1964) was an amateur in balloon flight.He designed a device toionization chamberSuspended under the balloon, the wall thickness of the ionization chamber is enough to withstand the pressure difference of one atmospheric pressure.He took the high pressure ionization chamber to high altitude by balloon,electrometerThe instructions oftemperature compensationRecord directly.He has made ten reconnaissance balloons, each of which is equipped with 2-3 ionization chambers that can work at the same time.
1911The first balloon rose to a height of 1070 meters. Below that height, the radiation was about the same as the sea level.The next year, his balloon soared to 5350 meters.He found that 700 meters above the ground,Ionization degreeSome drops (caused by the reduction of background caused by ground radioactivity) seem to increase slightly above 800 meters, and then with the rise of balloons, ionization continues to increase.Between 1400 m and 2500 m, it obviously exceeds the value of sea level.At 5000 meters above sea level, the radiation intensity is 9 times that of the ground.Since the results of daytime and nighttime measurements are the same, Hess concluded that the radiation was not from the sun, but from space.
Hess believes that a new hypothesis should be put forward: "This unknown thing is mainly found at high altitude... It may be penetrating radiation from space."1912Hess published a paper entitled "Penetrating radiation in the flight of seven free balloons" in the Journal of Physics.
Hess' discovery aroused great interest. Since then, the scientific community has conducted extensive research on various effects and origins of cosmic rays.At first, this radiation was called "Hess radiation", and later it was officially named "cosmic ray".At that time, many physicists doubted Hess's measurement and believed thatAtmospheric ionizationThe action does not come from space, but from geophysical phenomena, such as radioactivity emitted by certain materials that make up the crust.It is now believed that cosmic rays come from cosmic spaceHigh-energy particleThe general name of streams.
1914German physicist Werner Kolhorster (1887-1946) raised the balloon to 9300 meters, and the free current was 50 times larger than the sea level, which confirmed Hess's judgment.
1922American scientists Robert Andrews Millikan (1868-1953) (left) and I.S. Bowen carried out these experiments at a height of 55000 feet. In order to solve the source of this radiation, they first measured at the top of the mountain, and then lifted the unmanned balloon with electroscope and ionizer to measure the atmosphereIonization。
Summer 1925Millikan and his assistants are hereCaliforniaExperiments were carried out in the depths of Muir Lake and Arrowhead Lake in the mountains, trying to determine the source of cosmic rays by measuring the relationship between the ionization degree and the depth of the lake. The reason for choosing these two lakes is that they both use snow water as the water source, which can avoid radioactive pollution;Moreover, the two lakes are far apart, with a height difference of 6.675 feet, which can avoid mutual interference and facilitate comparison.
November 9, 1925, the National Academy of SciencesWisconsinWhen Madison held a meeting, Millikan reported the measurement results. His results showed that these rays did not originate from the earth or the lower atmosphere, but from the universe. Millikan agreed with most people at that time and believed that cosmic rays were a kind of high-frequencyelectromagnetic radiation, its frequency is much higher thanX-ray, which is 1000 times the average frequency of the latter.He believes that since the penetration of this kind of ray is much stronger than the hardest gamma ray, it will certainly not be composed of charged particles.If we assume that cosmic rays are really likeCathode rayThat wayCharged particle flow, then it can penetrate a lead block with a thickness of 6 feet, which will make these particles have unimaginable high energy at that time.If we assume that cosmic rays are generated byphoton(i.e. the quantum of electromagnetic radiation)Earth timeIts flight route will not be affected by geomagnetism;On the contrary, if the cosmic ray is composed of charged particles, it will definitely suffergeomagnetic fieldThere will be more charged particles of cosmic rays flying to high latitudes than to low latitudes, that is, there will be a "latitude effect". Millikan's measurement results show that cosmic rays come from all directions and are not affected by the sun, the Milky Way, the atmosphere or the geomagnetic latitude.
1927Dimitr Skobelzyn took pictures of cosmic ray traces in the cloud chamber, and confirmed the tracks of cosmic ray particles for the first time according to the tiny deflection of tracks in the cloud chamber.
1927-1929J. Clay (1882-1955), a Dutch physicist, went from the Netherlands to IndonesiaJavaDuring the trip, we found the trace of latitude effect - the intensity of cosmic rays near the equator is relatively low.
Bosch
The coincidence counting method proposed by Walther Bothe (1891-1957) wasGeiger counterHis innovation is to use two counter tubes, so that only when ionization collision occurs in two counter tubes at the same time, these two counter tubes can count.He uses the coincidence method to judge the energy andLaw of conservation of momentumWhether these laws are valid for each collision of photons and electrons, or whether they are established as a statistical average.To study the scatteredAlpha particleAnd recoil electrons. He and Geiger examined the singleCompton scatteringThe conclusion is that the law of conservation of energy and momentum is valid for every collision between photons and electrons.Since then, the coincidence method has been widely used in the study of cosmic rays.Around 1930, some important discoveries in the field of cosmic rays were almost inseparable from coincidence.The legitimate inventions are also nuclear physicsAlpha rayAnd ultrasonic research provides an effective tool.Both and Born shared the 1954The nobel prize in physics。
positron
In the autumn of 1931,At the International Conference on Nuclear Physics held in Rome, physicists proposed to MillikanElectromagnetic essenceThe hypothesis poses an open challenge.Italian physicist Bruno Benedetto Rossi (1905-1993) (right) proposed on the basis of analyzing a large number of experimental data: the cosmic rays observed from the sea level are essentially composed of charged particles with very high energy;According to the result of deflection display caused by strong magnetic field, their energy is about tens of billions of electron volts higher than Millikan's estimate.These charged particles may be in the atmosphereradiation sourceInitial high energyGamma radiationHowever, the energy of this gamma radiation (i.e. photon) is far higher than that released during Millikan's "atomic structure".There is a second possibility, that is, observed in cosmic raysHigh-energy particleIs the original cosmic radiation, or at least a meaningful part of it.
Millikan asked graduate student Anderson to useCloud chamber, directly measuring the energy of cosmic rays, but Anderson's work denied Millikan's hypothesis, and also led topositronDiscovery of.
1932, C.D. Anderson (1905-1991) (left) discovered the positron, which was the first remarkable achievement of cosmic ray research.
C. D. Anderson isCalifornia Institute of TechnologyStudents of physics professor R.A. Millikan have been doing cosmic ray research with Millikan since 1930.Since 1930 CD. Anderson is responsible for observing cosmic rays with a cloud chamber.Anderson uses aWilson Cloud ChamberTo study cosmic rays.He let the particles in the cosmic ray pass through the strong magnetic field in the room, quickly took pictures of the particle track, and then inferred the properties of the particles according to the track length, direction, radius of curvature and other data.
Strange track
August 2, 1932C. D. Anderson found a strange track in the picture. This track has the same deflection degree as the negative electron, but has the opposite direction (right picture), which shows that it is some kind of positively charged particle.fromcurvatureIt can't be proton.So he decisively concluded that this is a positively charged electron.The positron predicted by Dirac was thus discovered by Anderson.
At that time, CD. Anderson did not know Dirac's electron theory, let alone the possibility that he had predicted the existence of positrons.Dirac is in hisrelativityIn electronic theory.From his equation, we can see that electrons should have not only positive energy states, but also negative energy states.He believes that these negative energy states are usually occupied, and occasionally one state is empty, forming“hole”He wrote: "If there is a hole, it will be a new oneExperimental physicsThe unknown particle has the same mass as the electron and the same charge as the electron, but its symbol is different.We can call itAntielectron。”He also predicted: "It can be assumed that the proton will also have its own negative state... The state that is not fully occupied is represented as aAntiproton。”The prediction of antiproton was only confirmed by Emilio Segr è in 1945.
Blackett
British physicistBlackett(Baron Patrick Maynard Stuart Blackett, 1897-1974) Since 1921, improved Wilson cloud chamber photography technology to studyArtificial transformation of atomic nucleus。In 1924, he successfully verified artificial light for the first time with cloud chamber photosnuclear transmutationThat is, helium-14 nuclear captures alpha particles and turns them into oxygen-17.In 1925, he created a device for cloud chamber photography to be controlled by an automatic counter.Just a few months after C.D. Anderson discovered positrons, Blackett used his cosmic ray track photos of positrons and positrons pairing production to strongly confirm the existence of positrons.
Because the discovery of cosmic rays and positrons is closely related,Nobel Committee In 1936The nobel prize in physicsHess and Anderson were awarded these two related projects, and Blackett won the 1948 Nobel Prize in Physics for his improvement of Wilson Cloud Chamber and his series of discoveries in the field of nuclear physics and cosmic rays.
Compton
American physicist Arthur Holly Compton (1892-1962) (right) discoveredCompton effect(also known as "Compton scattering") won the Nobel Prize in Physics in 1927.His main interest is nuclear physics research. He foresees that nuclear energy will bring great benefits to mankind. In order to make full use of nuclear energy, Compton decided to study cosmic rays first. He plans to measure the intensity of cosmic rays in places with different magnetic latitudes and high elevations in 1932. Compton organized six expeditions to go to mountainsExtensive measurements were made in the low latitude area near the equator to make a reasonable judgment on whether the initial cosmic rays were photons or charged particles. Compton himself presided over two expeditions in the Rocky Mountains in the Midwest of the United States and the Alps in southern Europe, Australia, New Zealand, Peru and Canada.
March 18, 1932At the beginning of the expedition, Compton was inclined to accept Millikan's (photon) hypothesis. After extensive measurements, his view had a fundamental change. He concluded that the intensity of cosmic rays at sea level can be satisfactorily expressed as a function of the inclination of the geomagnetic field;The intensity of cosmic rays increases continuously with height, and the maximum value declared by Millikan does not exist at 9000 meters.Since September, Compton has received data measured by more than 60 scientists at 69 observation stations with a wide distribution, reflecting the geography of latitude from 78 ° north to 46 ° south and longitude from 175 ° east to 173 ° westLongitude and latitudeThe distribution of cosmic ray intensity within the range ofHigh-energy particle。
Millikan also made extensive observations in 1932.California Institute of TechnologyH.V. Neher, a young physicist, invented a highly sensitive automatic recordingElectroscope。The head of the Air Force agreed that Millikan could use bombers to carry measuring instruments to an altitude of more than 8000 meters.At the end of September, Millikan used balloons tostratosphereMeasurements were made.If cosmic rays are reallyCharged particle flowMillikan should be able to get the same conclusion from Compton, but their conclusions from observation are completely different (Millikan's article is shown on the left).
Physical Society
At the end of December 1932，American Physical SocietyAt the meeting held in Atlantic City, New Jersey, Millikan and ComptonNobel Prize in PhysicsThe winner had a heated debate on the nature of cosmic rays.Compton reported at the meeting that the intensity of cosmic rays at different latitudes is obviously different, indicating that the initial cosmic rays have the characteristics of charged particles, and proposed three experiments to support this view.Millikan read out the measurement results of Nehe's voyage across the equator at the Atlantic Conference, and found no latitude effect.Since both sides claim that they have experiments as evidence, they cannot unify their ideas, but most physicists have begun to recognize Compton's views.
November 11, 1935Two brave pilots (Albert W. Stevens and Orvil A. Anderson) drove the Explorer 2 helium balloon (with a volume of 113000 cubic feet) to the official record of 22066 meters, collecting atmospheric, cosmic ray and other data.
California Institute of TechnologySeth Neddermeyer (1907-1988) (right) and Carl D. Anderson put forward the hypothesis in 1934 that the trace with high penetration force is the trace of particles with mass between electrons and protons.(The left picture shows Anderson and Nedmeyer)
1936They found a particle with unit positive or negative charge in the cosmic ray, whose mass is 206.77 times that of the electron, and people think it isHideki Yukawa Predicted in 1930meson, call itMesonIt was later discovered that this particle does not actually participate in strong interaction and is a lepton, so it was renamedMuon。
In 1938, Pierre Auger (1899-1993) (right) discoveredExtensive air shower。The shower is a secondary produced by the impact of original high-energy particlesSubatomic particle。He found that the energy of the shower was as high as 1015 electron volts, which was 10 million times that known at that time.
March 9, 1940A Beech AD-17 biplane flew over the South Pole at 21050 feet above sea level to measure cosmic rays for the American expedition.
1946The team led by physicist Bruno Rossi and Georgi Zatsepin conducted the first experiment on the structure of air shower (right).The research team created the first array of related detectors to detect air showers.
1946Two British scientists George D. Rochester and Clifford C. Butler (1922-1999) took many photos of the cloud chamber event. In one of the photos, some tracks shaped like the letter V were found.Only particles with an approximate mass of 494MeV/c2 are admitted to decay into two in flightPionOnly when these tracks are generated can this be explained.It is believed that there is a new particle, which is called V particle according to its track shape (left figure).This V particle is now called K0 particle, which was later calledExotic particleThe beginning of the discovery of a series of new particles.
August 16, 1947Physicist Martin Pomerantz announced the release of four balloons with cosmic ray detectors (left), which passed at least 127000 feetAntarctic region。
1947Cecil Frank Powell (1903-1969) and others in the UK created the method of sending nuclear latex to high space by balloon to record cosmic raysboliviaThe π meson predicted by Yukawa Hideki in 1930 was found in the Andes region from cosmic rays. Its mass is about 273 times that of the electron. It has a strong interaction with the atomic nucleus, called the charged π meson.The pion exists for only 2.5 millionths of a second, and then it splits into a muon. The muon exists for a relatively long time, one millionth of a second, and flies at the speed of tens of thousands of kilometers per second.
1948Fred Hoyle, professor of astronomy at Cambridge University (1915-2001) (left), together with Hermann Bondi and Thomas Gold, proposed the "Theory of Stable Universe", which believes that the universe is the same on a large scale, including anytime and anywhere.In this“Steady state”There is no beginning and no end in the universe.The galaxy simply flies away in all directions, just like the raisins on the cake when baking the cake expand away.In order to fill the void left by the retrogression of galaxies and maintain the general appearance of the universe, they assumed that matterIntergalactic spaceThe rate of creation of matter (one particle per cubic kilometer per year) is just used to form new galaxies.
In 1948,George Gamow (1904-1968) and Ralph Asher Alpher (1921 -) also proposed that the universe is from a primitiveGaomiThe theory evolved from the state, and the famous nuclear physicist Hans Bethe was invited to sign his name. This theory is called Alpha, Bethe,&Gamow theory, which Hoyle called in 1952“Big Bang Theory”(the Big Bang), but he believes that the universe will not be created in an explosion.
1949Enrico Fermi (1901-1954) published the cosmic ray theory, trying to explain the particle acceleration mechanism of cosmic rays with the magnetic shock wave of supernova explosion, but not enough to explain the existence of the highest energy cosmic rays.
In 1962,Massachusetts Institute of TechnologyJohn Linsley and his colleagues usedNew MexicoThe 10 square kilometer air shower detector group of the volcanic farm detected a cosmic ray with an energy estimated at 1020 electron volts.
1965, Bell Telephone LaboratoryPenzias(Arno Penzias, 1933 - and R.W. Wilson accidentally discovered theCosmic microwave background radiation。They wanted to use a large communication antennaRadio astronomyHowever, due to the interference of a continuous background noise, the experiment cannot continue.The wavelength of the noise is 7.35cm, which is equivalent to 3.5kBlackbody radiation, whichIsotropyIt is extremely high and has nothing to do with seasonal changes.Almost one year, they tried every way to track and remove the noise, but it didn't work, so they calledPrinceton University Robert Henry Dick (1916~) described the problems he encountered and hoped that he could give an explanation.Dick immediately realized that what the two young people wanted to remove was exactly what Dick's research team was trying to find - something left over from the Big BangCosmic background radiation。Penzias and Wilson won theThe nobel prize in physics。
1966, Kenneth Grisen, Georgi Zatsepin and Vadem Kuzmin believed that the high-energy cosmic rays andMicrowave background radiationThe interaction reduces the energy, so the energy of cosmic rays should be less than 5 x 1019 electron volts.(The right picture is recorded by satelliteCosmic microwave background map）
Detection mode
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Direct detection method——For cosmic rays below 1014eV, the flux is large enough to use a particle detector with an area of about square meters to directly detect primitive cosmic rays.This type of detector requiresArtificial satelliteOr high-altitude balloon to prevent the atmosphere from absorbing cosmic rays.
Indirect detection method——For cosmic rays above 1014eV, due to the small flux, indirect measurement must be used to analyze the interaction between the original cosmic rays and the atmosphere to deduce the nature of the original cosmic rays.When cosmic rays hit atomic nuclei in the atmosphere, somebaryon, leptons and photons (gamma rays).These secondary particlesRepeated actionMore secondary particles are produced until the average energy is equal to some critical value, and the number of secondary particles reaches the maximum, which is called shower maximum. After that, the particles gradually decay or areAtmospheric absorptionThe number of secondary particles gradually decreases. This reaction is called "air shower".The main radiation source on the earth's surface is radioactive minerals. The secondary particles emitted by the air shower are the main radiation source at high altitude. The radiation is strongest at an altitude of 20km, and the radiation is strongest at an altitude of more than 100kmSpace radiationThe solar wind and cosmic rays are dominant.
The air shower is mainly composed of leptons and baryons.There are three ways to detect air shower: ground (and underground) array, Cherenkov telescope and fluorescent telescope.
Ground (and underground) arrays typically require multipleCharged particle detectorThe composition is distributed in a wide and flat area, so that secondary particles can have sufficient sampling and can be operated throughout the year.The Cherenkov telescope can detect the Cherenkov light generated by secondary particles, and the fluorescence telescope can detect the fluorescence generated by charged particle free nitrogen. These two telescopes can only be operated at night and need to avoid urban light sources. The average operation time is only 10%.
Cosmic rays are high-energy particles from outside the solar system, with energy ranging from 109eV to 1020eV.In space near the earth, about one cosmic ray passes through every square centimeter per second.The main components of cosmic rays are protons, and other nuclei from helium to iron, and even trace lanthanides.artificialParticle acceleratorIts maximum energy is about 1013eV.The right figure shows the energy spectrum of cosmic rays, spanning 12 orders of magnitude.There are two important energy spectraPhysical meaningThe turning point of 1015eV is called knee, and 3 ′ 1018eV is called ankle.Ultra High Energy Cosmic Rays: UHECR mainly studies cosmic rays above 1018eV.Why is there such high energy?Where do they come from?What particles are they?These are the research topics of cosmic ray physicists.
UHECR research funding increased rapidly after the termination of the U.S. Superconducting Super Collidea program, and has become one of the three main streams of astroparticle physics research (the other two areNeutrinoAnd dark matter).
The reason why the nuclei in cosmic rays can reach the earth from their remote source is because of the low density of matter in the universe.Nucleons have strong induction with other substances, so when cosmic rays approach the earth, they begin to collide with nucleons in atmospheric gases.In the process of particle rain, these collisions produce many π mesons and K mesons, which will quickly decay into unstable muons.Since there is no strong induction with the atmosphere and the relativistic effect of time expansion, many muons can reach the earth's surface.Muons are ionizing radiation and can be easily detected by many particle detectors, such as bubble chambers, orScintillator detector。If multiple muons are detected by different detectors at the same time, they must come from the same particle rain.
Now, new detection methods can detect these high-energy particles without particle rain, that is, in space, without the interference of the atmosphere, directly detect cosmic rays, such asAlpha magnetic spectrometerexperiment.
Main impacts
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Evolution of extraterrestrial life
Cosmic rays bombard the earth continuously, but a new study believes that this kind of invisible and intangibleHigh-energy particleFlow may play a key role in determining whether life exists on other planets.
More than 100 years after its discovery, cosmic rays still puzzle scientists.This flow of high-energy particles spreads almost at the speed of light in space, and some of them carry energy 100 million times higher than that achieved by the most powerful accelerator on the earth.Cosmic rays are nucleon streams, the main component of which is protons, that is, hydrogen nuclei.
When cosmic rays bombard the earth's atmosphere, they will produce a series of secondary particle streams, including muons, which are subatomic particles similar to electrons but with much greater mass.Some of these particle flows will reach the ground, endangering life on the ground and in the sea.In fact, muons can even penetrate tens of meters of surface rock and soil layers.
Scientists are studying the possible impact of cosmic rays on the habitability of distant exoplanets.In the past 20 years, scientists have used the ground andSpace telescopeThe equipment has found hundreds of exoplanets, which arouses people's hope that some form of extraterrestrial life may exist in those exoplanets.Researchers are particularly interested in exoplanets located in the so-called "habitable zone", where planets are located at a proper distance from stars, thus allowing water to exist on their surface in liquid form.On the earth, liquid water breeds rich life forms.
Researchers believe that the radiation level of a planet will affect its habitability.Although the external radiation flux experienced by a planet, the flux from its "sun" is far higher than the cosmic ray from the galaxy, but the particle energy of the latter is far higher than the photon and proton flow energy in the solar radiation, which makes it have an impact that cannot be ignored.
The author of this study, Dimitra Atri, is an astrophysicist from the Blue Marble Space Science Institute, a non-profit research organization composed of scientists from all over the world.Researchers have paid attention to two important factors that may affect the radiation dose received by the planet, including the strength of its magnetic field and the thickness of the atmosphere.
Aiteli said, "I began to think about this problem when I was studying Mars and the Earth. These two planets are close neighbors, but the Earth has a thriving biosphere, but Mars is desolate. Why?" He said, "The main reason is that the environmental radiation flux of Mars is very high compared with the Earth.This is because the atmosphere of Mars is almost negligible compared with that of the Earth. By the standards of the Earth, it is very, very thin.In addition, Mars also has no global magnetic field, so it correspondingly lacks the protective layer facing cosmic rays as the Earth does.So I think it is this difference that leads to the completely different fate of the two originally similar planets. "
The researchers simulated different planetary scenarios, from planets that lack magnetic field completely to planets with strong magnetic field like the Earth;From planets with very thin atmospheres to planets with dense atmospheres like Earth.Aiteli said: "We know that the earth's magnetic field protects us from cosmic rays, and we also believe that cosmic rays are a factor that significantly affects the radiation flux of the ground environment."
However, unexpectedly, Aiteli said: "We found that the thickness of the planet's atmosphere is the more important factor for the radiation flux on the planet's surface."He said: "If you take the Earth as an example, if you completely remove the magnetic field of the Earth, then the radiation flux we are exposed to in the environment will rise twice, which is a very big increase, but even so, it will not pose a serious threat to our survival.However, if you keep the magnetic field, but reduce the concentration of the earth's atmosphere by 10 times, then the radiation flux we receive will rise by two orders of magnitude. "
Scientists now tend to think that exoplanets orbiting red dwarfs are ideal places to search for extraterrestrial life, because such stars are relatively weak, and their number is the largest in the universe, accounting for about 80% of the total number of stars in the universe.However, statistical studies show that exoplanets in habitable zones relatively close to red dwarfs tend to have weaker magnetic fields, which is called“Super Earth”This is especially true of exoplanets.The so-called "super earth" refers to those rocky planets whose mass is below 10 times the mass of the earth.Astrobiologists believe that the weak magnetic field of these planets may make them unsuitable for life. However, this discovery shows that the weak magnetic field may not pose a major problem.
Aiteli said that further research in the future will examine how the increased radiation flux will affect the evolution of life.He said: "The current research on the effect of radiation dose on organisms is mainly to use very high radiation dose to investigate how organisms will be harmed and whether they will die in such an environment. But I think that a systematic study of the reaction of organisms in an environment with gradually increasing radiation dose will better provide a reference for the study of the impact of cosmic rays on livable environments."
Aiteli and his colleagues have detailed their findings in the October issue of Astrobiology.[5]
Manned space flight
Cosmic rays are affected by the earth's atmosphere, and the natural background radiation to a single person on the ground is only 0.3-0.4 mSv/y.Outside the atmosphere, about one proton or heavier atomic nucleus passes through the nail size area every second. In total, about 5000 ions pass through the astronaut's body every second, breaking the chemical bonds in the body and causing a series of ionization reactions.In cosmic rays, a few heavier nucleons will cause more damage than protons, because the ability to break chemical bonds is proportional to the square of the charge.For example, iron nuclei cause 676 times more damage than protons.according toNASA(NASA) estimates that astronauts receive 250 mSv radiation every year in the space of the solar system, and about 1/3 of their DNA will be cut off by cosmic rays.70-120mSv/y on the lunar surface and 100mSv/y in low Earth orbit,Van Allen radiation belt15 Sv/y.The sun will also release a large number of protons and heavy atomic nuclei at a speed close to the speed of light, sometimes exceeding Sv within an hour, which is a lethal dose for astronauts without barriers.[6]
Development and utilization
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The subatomic particles produced by cosmic ray collisions have been used to create a new type of global positioning system (GPS).In a new study published in iSicence, scientists from the University of Tokyo in Japan showed how they can use these high-energy particles to navigate in buildings, underground or deep underwater.[8]
