Antimatter synthesis. Exactly the opposite
ANTIMATTER, a substance consisting of atoms whose nuclei have a negative electrical charge and are surrounded by positrons - electrons with a positive electrical charge. In ordinary matter, from which the world around us is built, positively charged nuclei are surrounded by negatively charged electrons. To distinguish it from antimatter, ordinary matter is sometimes called coinematter (from the Greek. koinos- ordinary). However, this term is practically not used in Russian literature. It should be emphasized that the term “antimatter” is not entirely correct, since antimatter is also a substance, a type of it. Antimatter has the same inertial properties and creates the same gravitational attraction as ordinary matter.
When talking about matter and antimatter, it is logical to start with elementary (subatomic) particles. Each elementary particle has an antiparticle; both have almost the same characteristics, except that they have opposite electrical charges. (If the particle is neutral, then the antiparticle is also neutral, but they can differ in other characteristics. In some cases, the particle and antiparticle are identical to each other.) Thus, an electron, a negatively charged particle, corresponds to a positron, and the antiparticle of a proton with a positive charge is a negatively charged antiproton. The positron was discovered in 1932, and the antiproton in 1955; these were the first antiparticles discovered. The existence of antiparticles was predicted in 1928 on the basis of quantum mechanics by the English physicist P. Dirac.
When an electron and a positron collide, they annihilate, i.e. both particles disappear, and two gamma rays are emitted from the point of their collision. If the colliding particles move at low speed, then the energy of each gamma quantum is 0.51 MeV. This energy is the electron's "rest energy", or its rest mass, expressed in energy units. If the colliding particles move at high speed, then the energy of gamma rays will be greater due to their kinetic energy. Annihilation also occurs when a proton collides with an antiproton, but the process in this case is much more complicated. A number of short-lived particles are born as intermediate products of the interaction; however, after a few microseconds, neutrinos, gamma rays and a small number of electron-positron pairs remain as the final products of transformations. These pairs can eventually annihilate, creating additional gamma rays. Annihilation also occurs when an antineutron collides with a neutron or proton.
Since antiparticles exist, the question arises whether antinuclei can be formed from antiparticles. The nuclei of ordinary matter atoms consist of protons and neutrons. The simplest nucleus is the nucleus of the isotope of ordinary hydrogen 1 H; it represents a single proton. The deuterium 2H nucleus consists of one proton and one neutron; it's called a deuteron. Another example of a simple nucleus is the 3 He nucleus, consisting of two protons and one neutron. The antideuteron, consisting of an antiproton and an antineutron, was obtained in the laboratory in 1966; The anti-3He nucleus, consisting of two antiprotons and one antineutron, was first obtained in 1970.
According to modern particle physics, with the appropriate technical means, it would be possible to obtain the antinuclei of all ordinary nuclei. If these antinuclei are surrounded by the proper number of positrons, then they form antiatoms. Antiatoms would have almost exactly the same properties as ordinary atoms; they would form molecules, from which solids, liquids and gases, including organic substances, could be formed. For example, two antiprotons and one antioxygen nucleus, together with eight positrons, could form an antiwater molecule similar to ordinary water H 2 O, each molecule of which consists of two protons of hydrogen nuclei, one oxygen nucleus and eight electrons. Modern particle theory is able to predict that antiwater will freeze at 0°C, boil at 100°C, and otherwise behave like ordinary water. Continuing such reasoning, we can come to the conclusion that an anti-world built from antimatter would be extremely similar to the ordinary world around us. This conclusion serves as the starting point for theories of a symmetrical universe, based on the assumption that the universe contains equal amounts of ordinary matter and antimatter. We live in that part of it that consists of ordinary matter.
If two identical pieces of substances of opposite types are brought into contact, then the annihilation of electrons with positrons and nuclei with antinuclei will occur. In this case, gamma quanta will appear, by the appearance of which one can judge what is happening. Since the Earth, by definition, consists of ordinary matter, there are no appreciable amounts of antimatter in it, except for the tiny number of antiparticles produced in large accelerators and in cosmic rays. The same applies to the entire solar system.
Observations show that only a limited amount of gamma radiation is produced within our Galaxy. From this, a number of researchers conclude that there are no noticeable amounts of antimatter in it. But this conclusion is not indisputable. There is currently no way to determine, for example, whether a given nearby star is composed of matter or antimatter; an antimatter star emits exactly the same spectrum as a normal star. Further, it is quite possible that the rarefied matter that fills the space around the star and is identical to the matter of the star itself is separated from areas filled with matter of the opposite type - very thin high-temperature “Leidenfrost layers”. Thus, we can talk about a “cellular” structure of interstellar and intergalactic space, in which each cell contains either matter or antimatter. This hypothesis is supported by modern research showing that the magnetosphere and heliosphere (interplanetary space) have a cellular structure. Cells with different magnetizations and sometimes also different temperatures and densities are separated by very thin current shells. This leads to a paradoxical conclusion that these observations do not contradict the existence of antimatter even within our Galaxy.
If previously there were no convincing arguments in favor of the existence of antimatter, now the successes of X-ray and gamma-ray astronomy have changed the situation. Phenomena associated with a huge and often highly disordered release of energy have been observed. Most likely, the source of such energy release was annihilation.
Swedish physicist O. Klein developed a cosmological theory based on the hypothesis of symmetry between matter and antimatter, and came to the conclusion that annihilation processes play a decisive role in the evolution of the Universe and the formation of the structure of galaxies.
It is becoming increasingly clear that the main alternative theory, the “big bang” theory, seriously contradicts observational data and “symmetric cosmology” is likely to occupy a central place in solving cosmological problems in the near future.
Antimatter is matter consisting solely of antiparticles. In nature, every elementary particle has an antiparticle. For an electron it will be a positron, and for a positively charged proton it will be an antiproton. Atoms of ordinary matter - otherwise it is called coine substance- consist of a positively charged nucleus around which electrons move. And the negatively charged nuclei of antimatter atoms, in turn, are surrounded by antielectrons.
The forces that determine the structure of matter are the same for both particles and antiparticles. Simply put, particles differ only in the sign of their charge. It is characteristic that “antimatter” is not quite the correct name. It is essentially just a type of substance that has the same properties and is capable of creating attraction.
Annihilation
In fact, this is the process of collision between a positron and an electron. As a result, mutual destruction (annihilation) of both particles occurs with the release of enormous energy. The annihilation of 1 gram of antimatter is equivalent to the explosion of a 10 kiloton TNT charge!
Synthesis
In 1995, it was announced that the first nine antihydrogen atoms had been synthesized. They lived for 40 nanoseconds and died, releasing energy. And already in 2002, the number of atoms obtained was in the hundreds. But all the resulting antiparticles could only survive for nanoseconds. Things changed with the launch of the hadron collider: they managed to synthesize 38 antihydrogen atoms and hold them for a full second. During this period of time, it became possible to conduct some research into the structure of antimatter. They learned to retain particles after creating a special magnetic trap. In order to achieve the desired effect, a very low temperature is created. True, such a trap is a very cumbersome, complex and expensive affair.
In S. Snegov’s trilogy “People Like Gods,” the annihilation process is used for intergalactic flights. The heroes of the novel, using it, turn stars and planets into dust. But in our time, obtaining antimatter is much more difficult and expensive than feeding humanity.
How much does antimatter cost?
One milligram of positrons should cost 25 billion dollars. And for one gram of antihydrogen you will have to pay 62.5 trillion dollars.
A person so generous has not yet appeared that he could buy even one hundredth of a gram. Several hundred million Swiss francs had to be paid for one billionth of a gram to obtain material for experimental work on the collision of particles and antiparticles. So far there is no substance in nature that would be more expensive than antimatter.
But with the question of the weight of antimatter, everything is quite simple. Since it differs from ordinary matter only in charge, all other characteristics are the same. It turns out that one gram of antimatter will weigh exactly one gram.
World of antimatter
If we accept as true that there was, then as a result of this process equal amounts of both matter and antimatter should have arisen. So why don’t we observe objects made of antimatter near us? The answer is quite simple: the two types of matter cannot coexist together. They will definitely destroy each other. It is likely that galaxies and even universes made of antimatter exist, and we even see some of them. But the same radiation emanates from them, the same light comes from them, as from ordinary galaxies. Therefore, it is still impossible to say for sure whether the antiworld exists or is this a beautiful fairy tale.
Is it dangerous?
Humanity has turned many useful discoveries into means of destruction. Antimatter in this sense cannot be an exception. It is not yet possible to imagine a more powerful weapon than one based on the principle of annihilation. Perhaps it’s not so bad that it’s not yet possible to extract and store antimatter? Will it become a fatal bell that humanity will hear on its last day?
Recently, members of the ALICE collaboration at CERN measured the masses of antimatter nuclei with record accuracy and even estimated the energy that binds antiprotons to antineutrons in them. So far, no significant difference between these parameters in matter and antimatter has been found, but this is not the main thing. It is important that right now, in the last few years, not only antiparticles, but also antinuclei and even antiatoms are becoming available for measurements and observations. This means it’s time to figure out what antimatter is and what place its research takes in modern physics.
Let's try to guess some of your first questions about antimatter.
Is it true that a super-powerful bomb can be made using antimatter? Is it possible that antimatter is actually being accumulated at CERN, as shown in the movie Angels and Demons, and that it is very dangerous? Is it true that antimatter will be an extremely efficient fuel for space travel? Is there any truth to the idea of a positronic brain that Isaac Asimov endowed robots with in his works?...
It is no secret that for most people antimatter is associated with something extremely (explosively) dangerous, with something suspicious, with something that excites the imagination with fantastic promises and huge risks - hence such questions. Let’s admit: the laws of physics do not directly prohibit all this. However, the implementation of these ideas is so far from reality, from modern technologies and from the technologies of the next decades, that the pragmatic answer is simple: no, for the modern world this is not true. Conversation on these topics is simply fantasy, based not on real scientific and technical achievements, but on their extrapolation far beyond the limits of modern capabilities. If you want to have a serious conversation about these topics, come closer to 2100. For now, let's talk about actual scientific research on antimatter.
What is antimatter?
Our world is designed in such a way that for each type of particle - electrons, protons, neutrons, etc. - there are antiparticles (positrons, antiprotons, antineutrons). They have the same mass and, if they are unstable, the same half-life, but opposite charges and other numbers characterizing the interaction. Positrons have the same mass as electrons, but only a positive charge. Antiprotons have a negative charge. Antineutrons are electrically neutral, just like neutrons, but have the opposite baryon number and are composed of antiquarks. An antinucleus can be assembled from antiprotons and antineutrons. By adding positrons, we create antiatoms, and by accumulating them, we get antimatter. This is all antimatter.
And here there are several interesting subtleties that are worth talking about. First of all, the very existence of antiparticles is a huge triumph of theoretical physics. This non-obvious, and for some even shocking, idea was theoretically derived by Paul Dirac and was initially received with hostility. Moreover, even after the discovery of positrons, many still doubted the existence of antiprotons. Firstly, they said, Dirac came up with his own theory to describe the electron, and it is not a fact that it will work for the proton. For example, the magnetic moment of the proton differs several times from the prediction of the Dirac theory. Secondly, they searched for traces of antiprotons in cosmic rays for a long time, but nothing was found. Thirdly, they argued - literally repeating our words - that if there are antiprotons, then there must be antiatoms, antistars and antigalaxies, and we would definitely notice them in grandiose cosmic explosions. Since we don’t see this, it’s probably because antimatter doesn’t exist. Therefore, the experimental discovery of the antiproton in 1955 at the newly launched Bevatron accelerator was a rather non-trivial result, awarded the Nobel Prize in Physics for 1959. In 1956, the antineutron was discovered at the same accelerator. The story of these searches, doubts, and achievements can be found in numerous historical essays, for example, in this report or in Frank Close's recent book Antimatter.
However, it must be said separately that healthy doubt in purely theoretical statements is always useful. For example, the statement that antiparticles have the same mass as particles is also a theoretical result; it follows from a very important CPT theorem. Yes, the modern, experimentally tested physics of the microworld is built on this statement. But it’s still an equality: who knows, maybe this way we’ll find the limits of applicability of the theory.
Another feature: not all forces of the microworld relate equally to particles and antiparticles. For electromagnetic and strong interactions there is no difference between them, for weak ones there is. Because of this, some subtle details of the interactions of particles and antiparticles differ, for example, the probabilities of the decay of particle A into a set of particles B and anti-A into a set of anti-B (for more details about the differences, see Pavel Pakhov’s collection). This feature arises because weak interactions break the CP symmetry of our world. But why this happens is one of the mysteries of elementary particles, and it requires going beyond the limits of the known.
Here's another subtlety: some particles have so few characteristics that antiparticles and particles do not differ from each other at all. Such particles are called truly neutral. This is a photon, a Higgs boson, neutral mesons, consisting of quarks and antiquarks of the same type. But the situation with neutrinos is still unclear: maybe they are truly neutral (Majorana), or maybe not. This is of critical importance for the theory describing the masses and interactions of neutrinos. The answer to this question will really be a major step forward, because it will help us understand the structure of our world. The experiment has not yet said anything unambiguous about this. But the experimental program for neutrino research is so powerful, there are so many experiments being carried out that physicists are gradually getting closer to the solution.
Where is this antimatter?
When an antiparticle meets its particle, it annihilates: both particles disappear and turn into a set of photons or lighter particles. All rest energy turns into the energy of this micro-explosion. This is the most efficient conversion of mass into thermal energy, hundreds of times more efficient than a nuclear explosion. But we don’t see any grandiose natural explosions around us; Antimatter does not exist in appreciable quantities in nature. However, individual antiparticles may well be born in a variety of natural processes.
The easiest way is to create positrons. The simplest option is radioactivity, the decay of some nuclei due to positive beta radioactivity. For example, in experiments the isotope sodium-22 with a half-life of two and a half years is often used as a source of positrons. Another, rather unexpected natural source is during which flashes of gamma radiation from the annihilation of positrons are sometimes detected, which means that positrons were somehow born there.
It is more difficult to create antiprotons and other antiparticles: there is not enough radioactive decay energy for this. In nature, they are born under the influence of high-energy cosmic rays: a cosmic proton, colliding with some molecule in the upper layers of the atmosphere, generates streams of particles and antiparticles. However, this happens up there, antiprotons almost never reach the ground (which was unknown to those who were looking for antiprotons in cosmic rays in the 40s), and you can’t bring this source of antiprotons to the laboratory.
In all physics experiments, antiprotons are produced by “brute force”: they take a beam of high-energy protons, direct it to a target, and sort out the “hadron scraps” that are produced in large quantities in this collision. Sorted antiprotons are output in the form of a beam, and then they are either accelerated to high energies in order to collide with protons (this is how, for example, the American Tevatron collider worked), or, conversely, they are slowed down and used for more subtle measurements.
At CERN, which can rightly be proud of a long history of antimatter research, there is a special “accelerator” AD, the “Antiproton Moderator”, which does just this task. It takes a beam of antiprotons, cools them (i.e., slows them down), and then distributes the flow of slow antiprotons over several special experiments. By the way, if you want to look at the state of AD in real time, then Cernov online monitors allow this.
It is already very difficult to synthesize antiatoms, even the simplest ones, antihydrogen atoms. They do not arise in nature at all - there are no suitable conditions. Even in the laboratory, many technical difficulties must be overcome before antiprotons deign to combine with positrons. The problem is that the antiprotons and positrons emitted from the sources are still too hot; they will simply collide with each other and fly apart, rather than forming an anti-atom. Physicists still overcome these difficulties, but with rather cunning methods (as is done in one of the ASACUSA Cern experiments).
What is known about antinuclei?
All antiatomic achievements of mankind relate only to antihydrogen. Antiatoms of other elements have not yet been synthesized in the laboratory or observed in nature. The reason is simple: antinuclei are even more difficult to create than antiprotons.
The only way we know to create antinuclei is to collide heavy nuclei of high energies and see what happens there. If the collision energy is high, thousands of particles, including antiprotons and antineutrons, will be born and scatter in all directions. Antiprotons and antineutrons accidentally emitted in one direction can combine with each other to form an antinucleus.
The ALICE detector can distinguish between different nuclei and antinuclei based on their energy release and the direction of twist in a magnetic field.
Image: CERN
The method is simple, but not too ineffective: the probability of synthesizing a nucleus in this way drops sharply as the number of nucleons increases. The lightest antinuclei, antideuterons, were first observed exactly half a century ago. Antihelium-3 was seen in 1971. Antitriton and antihelium-4 are also known, the latter being discovered quite recently, in 2011. Heavier antinuclei have not yet been observed.
Two parameters describing nucleon-nucleon interactions (scattering length f0 and effective radius d0) for different pairs of particles. The red asterisk is the result for a pair of antiprotons obtained by the STAR collaboration.
Unfortunately, you cannot make antiatoms this way. Antinuclei are not only produced rarely, but also have too much energy and fly out in all directions. Trying to catch them at a collider and then take them through a special channel and cool them is unrealistic.
However, sometimes it is enough to carefully track antinuclei in flight to obtain some interesting information about the antinuclear forces acting between antinucleons. The simplest thing is to carefully measure the mass of antinuclei, compare it with the sum of the masses of antiprotons and antineutrons, and calculate the mass defect, i.e. nuclear binding energy. It is recently operating at the Large Hadron Collider; The binding energy for antideuteron and antihelium-3 coincided within the limits of error with ordinary nuclei.
Another, more subtle effect was studied by the STAR experiment at the American heavy ion collider RHIC. He measured the angular distribution of the produced antiprotons and found out how it changes when two antiprotons are emitted in a very close direction. Correlations between antiprotons made it possible for the first time to measure the properties of the “antinuclear” forces acting between them (scattering length and effective interaction radius); they coincided with what is known about the interaction of protons.
Is there antimatter in space?
When Paul Dirac deduced the existence of positrons from his theory, he fully assumed that real antiworlds could exist somewhere in space. Now we know that there are no stars, planets, or galaxies made of antimatter in the visible part of the Universe. The point is not even that annihilation explosions are not visible; It is simply completely unimaginable how they could ever have formed and survived to the present day in a constantly evolving universe.
But the question “how did this happen” is another huge mystery of modern physics; in scientific language it is called the problem of baryogenesis. According to the cosmological picture of the world, in the earliest universe there were equal numbers of particles and antiparticles. Then, due to the violation of CP symmetry and the baryon number, a small, at the level of one billionth, excess of matter over antimatter should have appeared in a dynamically developing universe. As the universe cooled, all antiparticles annealed with particles; only this excess of matter survived, which gave birth to the universe that we observe. It is because of him that at least something interesting remains in it, it is thanks to him that we exist at all. How exactly this asymmetry arose is unknown. There are many theories, but which one is true is unknown. It is only clear that this must definitely be some kind of New Physics, a theory that goes beyond the Standard Model, beyond the boundaries of what has been experimentally verified.
Three options for where antiparticles in high-energy cosmic rays can come from: 1 - they can simply arise and accelerate in a “cosmic accelerator”, for example in a pulsar; 2 - they can be born during collisions of ordinary cosmic rays with atoms of the interstellar medium; 3 - they can arise during the decay of heavy dark matter particles.
Although there are no planets or stars made of antimatter, antimatter is still present in space. Fluxes of positrons and antiprotons of different energies are recorded by satellite cosmic ray observatories, such as PAMELA, Fermi, AMS-02. The fact that positrons and antiprotons come to us from space means that they are born somewhere out there. The high-energy processes that can generate them are known in principle: these are highly magnetized neighborhoods of neutron stars, various explosions, acceleration of cosmic rays at shock wave fronts in the interstellar medium, etc. The question is whether they can explain all the observed properties of the flow of cosmic antiparticles. If it turns out not, this will be evidence in favor of the fact that some of them arise from the decay or annihilation of dark matter particles.
There is also a mystery here. In 2008, the PAMELA observatory discovered a suspiciously large number of high-energy positrons compared to what theoretical modeling predicted. These results were recently confirmed by the AMS-02 installation - one of the modules of the International Space Station and, in general, the largest detector of elementary particles launched into space (and assembled, guess where? - correctly, at CERN). This excess of positrons excites the minds of theorists - after all, it may not be “boring” astrophysical objects that are responsible for it, but heavy dark matter particles that decay or annihilate into electrons and positrons. There is no clarity here yet, but the AMS-02 installation, as well as many critical physicists, are studying this phenomenon very carefully.
The ratio of antiprotons to protons in cosmic rays of different energies. The dots are experimental data, the multi-colored curves are astrophysical expectations with various errors.
Image: Cornell University Library
The situation with antiprotons is also unclear. In April of this year, AMS-02 presented preliminary results of a new cycle of research at a special scientific conference. The main highlight of the report was the assertion that AMS-02 sees too many high-energy antiprotons - and this could also be a hint at the decay of dark matter particles. However, other physicists do not agree with such a cheerful conclusion. It is now believed that the antiproton data from AMS-02, with some stretch, can be explained by conventional astrophysical sources. One way or another, everyone is eagerly awaiting the new positron and antiproton data from AMS-02.
AMS-02 has already detected millions of positrons and a quarter of a million antiprotons. But the creators of this installation have a bright dream - to catch at least one antinucleus. This will be a real sensation - it is absolutely incredible that antinuclei would be born somewhere in space and fly to us. So far, no such case has been discovered, but data collection continues, and who knows what surprises nature has in store for us.
Antimatter - anti-gravity? How does she even feel gravity?
If we rely only on experimentally verified physics and do not go into exotic, as yet unconfirmed theories, then gravity should act on antimatter in exactly the same way as on matter. No antigravity is expected for antimatter. If we allow ourselves to look a little further, beyond the limits of the known, then purely theoretically possible options are when, in addition to the usual universal gravitational force, there is something additional that acts differently on matter and antimatter. No matter how illusory this possibility may seem, it needs to be verified experimentally, and for this it is necessary to carry out experiments to test how antimatter feels the earth's gravity.
For a long time it was not really possible to do this for the simple reason that for this it is necessary to create individual antimatter atoms, trap them, and conduct experiments with them. Now we have learned how to do this, so the long-awaited test is just around the corner.
The main supplier of the results is the same CERN with its extensive program for the study of antimatter. Some of these experiments have already indirectly verified that antimatter’s gravity is fine. For example, he discovered that the (inert) mass of the antiproton coincides with the mass of the proton with very high accuracy. If gravity had acted differently on antiprotons, physicists would have noticed the difference - after all, the comparison was made in the same installation and under the same conditions. The result of this experiment: the effect of gravity on antiprotons coincides with the effect on protons with an accuracy of better than one millionth.
However, this measurement is indirect. To be more convincing, I would like to conduct a direct experiment: take several antimatter atoms, drop them and see how they fall in a gravitational field. Such experiments are also being conducted or prepared at CERN. The first attempt was not very impressive. In 2013, the ALPHA experiment - which by then had already learned to hold a cloud of antihydrogen in its trap - tried to determine where the antiatoms would fall if the trap was turned off. Unfortunately, due to the low sensitivity of the experiment, it was not possible to obtain an unambiguous answer: too little time had passed, the antiatoms were rushing back and forth in the trap, and outbreaks of annihilation occurred here and there.
Two other Cern experiments promise to radically improve the situation: GBAR and AEGIS. Both of these experiments will test in different ways how a cloud of ultra-cold antihydrogen falls in a gravitational field. Their expected accuracy in measuring the acceleration of gravity for antimatter is about 1%. Both installations are currently in the assembly and debugging stage, and main research will begin in 2017, when the AD antiproton moderator will be complemented by the new ELENA storage ring.
Variants of positron behavior in solid matter.
Image: nature.com
What happens if a positron enters matter?
Formation of molecular positronium on a quartz surface.
Image: Clifford M. Surko / Atomic physics: A whiff of antimatter soup
If you have read this far, you already know very well that as soon as a particle of antimatter enters ordinary matter, annihilation occurs: the particles and antiparticle disappear and turn into radiation. But how quickly does this happen? Let's imagine a positron that flew from a vacuum and entered a solid substance. Will it annihilate upon contact with the first atom? Not at all necessary! The annihilation of an electron and a positron is not an instantaneous process; it requires a long time on atomic scales. Therefore, the positron manages to live a bright life in matter, full of non-trivial events.
First, a positron can pick up an orphan electron and form a bound state, positronium (Ps). Given a suitable spin orientation, positronium can live for tens of nanoseconds before annihilation. Being in solid matter, during this time it will have time to collide with atoms millions of times, because the thermal speed of positronium at room temperature is about 25 km/sec.
Secondly, drifting in a substance, positronium can come to the surface and stick there - this is a positronic (or rather, positronium) analogue of atomic adsorption. At room temperature, it does not sit in one place, but actively travels along the surface. And if this is not an external surface, but a nanometer-sized pore, then positronium becomes trapped in it for a long time.
Further more. In the standard material for such experiments, porous quartz, the pores are not isolated, but are connected by nanochannels into a common network. Warm positronium, crawling along the surface, will have time to examine hundreds of pores. And since a lot of positronium is formed in such experiments and almost all of them crawl out into the pores, sooner or later they bump into each other and, interacting, sometimes form real molecules - molecular positronium, Ps 2. Then you can study how positronium gas behaves, what excited states positronium has, etc. And don't think that these are purely theoretical considerations; All of these effects have already been tested and studied experimentally.
Does antimatter have practical applications?
Of course. In general, any physical process, if it opens up to us some new facet of our world and does not require any extra costs, will certainly find practical applications. Moreover, such applications that we ourselves would not have imagined if we had not discovered and first studied the scientific side of this phenomenon.
The best known application of antiparticles is PET, positron emission tomography. In general, nuclear physics has an impressive track record of medical applications, and antiparticles are not idle here either. With PET, a small dose of a drug is injected into the patient's body, containing an unstable isotope with a short lifetime (minutes to hours) and decaying due to positive beta decay. The drug accumulates in the desired tissues, the nuclei decay and emit positrons, which annihilate nearby and produce two gamma quanta of a certain energy. The detector registers them, determines the direction and time of their arrival, and restores the place where the decay occurred. This makes it possible to construct a three-dimensional map of the distribution of matter with high spatial resolution and with a minimum radiation dose.
Positrons can also be used in materials science, for example, to measure the porosity of a substance. If the substance is continuous, then positrons stuck in the substance at a sufficient depth annihilate quite quickly and emit gamma rays. If there are nanopores inside the substance, annihilation is delayed because positronium sticks to the surface of the pore. By measuring this delay, it is possible to determine the degree of nanoporosity of a substance using a non-contact and non-destructive method. This technique is illustrated by recent work on how nanopores appear and close in the thinnest layer of ice when vapor is deposited on the surface. A similar approach also works when studying structural defects in semiconductor crystals, for example, vacancies and dislocations, and allows one to measure the structural fatigue of the material.
Antiprotons may also have medical applications. Now at the same CERN the ACE experiment is being conducted, which studies the effect of an antiproton beam on living cells. Its goal is to study the prospects for using antiprotons for cancer therapy.
Energy release of an ion beam and x-rays when passing through a substance.
Image: Johannes Gutleber/CERN
This idea may terrify the reader out of habit: how can it be that an antiproton beam hits a living person?! Yes, and it’s much safer than irradiating a deep tumor with x-rays! An antiproton beam of specially selected energy becomes in the hands of a surgeon an effective tool with which it is possible to burn out tumors deep inside the body and minimize the impact on surrounding tissues. Unlike X-rays, which burn everything that falls under the beam, heavy charged particles on their way through matter release the bulk of their energy in the last centimeters before stopping. By adjusting the energy of the particles, you can vary the depth at which the particles stop; It is this region, measuring millimeters in size, that will bear the main radiation impact.
This type of proton beam radiotherapy has long been used in many well-equipped clinics around the world. Recently, some of them have switched to ion therapy, which uses a beam of carbon ions rather than protons. For them, the energy release profile is even more contrasting, which means that the effectiveness of the “therapeutic effects versus side effects” pair increases. But it has long been proposed to try antiprotons for this purpose. After all, when they enter a substance, they not only give up their kinetic energy, but also annihilate after stopping - and this increases the energy release several times. Where this extra energy is deposited is a complex question and needs to be carefully studied before clinical trials are launched.
This is exactly what the ACE experiment does. In it, researchers pass a beam of antiprotons through a cuvette containing a bacterial culture and measure their survival as a function of location, beam parameters, and physical characteristics of the environment. This methodical and perhaps boring collection of technical data is an important initial stage of any new technology.
Igor Ivanov
Ecology of knowledge: Antimatter has long been the subject of science fiction. In the book and movie Angels and Demons, Professor Langdon tries to save the Vatican from an antimatter bomb. The Star Trek starship Enterprise uses an engine based on
Antimatter has long been the subject of science fiction. In the book and movie Angels and Demons, Professor Langdon tries to save the Vatican from an antimatter bomb. Star Trek's Starship Enterprise uses annihilating antimatter propulsion to travel faster than the speed of light. But antimatter is also an object of our reality. Antimatter particles are virtually identical to their material partners, except that they carry opposite charge and spin. When antimatter meets matter, they instantly annihilate into energy, and this is no longer fiction.
Although antimatter bombs and ships powered by the same fuel are not yet practical possibilities, there are many facts about antimatter that will surprise you or refresh your memory of what you already knew.
1. Antimatter should have destroyed all matter in the Universe after the Big Bang
According to the theory, the Big Bang created matter and antimatter in equal quantities. When they meet, mutual destruction occurs, annihilation, and only pure energy remains. Based on this, we should not exist.
But we exist. And as far as physicists know, this is because for every billion matter-antimatter pairs there was one extra particle of matter. Physicists are trying their best to explain this asymmetry.
2. Antimatter is closer to you than you think
Small amounts of antimatter constantly rain down on Earth in the form of cosmic rays, energetic particles from space. These antimatter particles reach our atmosphere at levels ranging from one to more than a hundred per square meter. Scientists also have evidence that antimatter is created during thunderstorms.
There are other sources of antimatter that are closer to us. Bananas, for example, produce antimatter by emitting one positron—the antimatter equivalent of an electron—about once every 75 minutes. This is because bananas contain small amounts of potassium-40, a naturally occurring isotope of potassium. The decay of potassium-40 sometimes produces a positron.
Our bodies also contain potassium-40, which means you emit positrons too. Antimatter annihilates instantly upon contact with matter, so these antimatter particles don't last very long.
3. People managed to create very little antimatter
The annihilation of antimatter and matter has the potential to release enormous amounts of energy. A gram of antimatter can produce an explosion the size of a nuclear bomb. However, people have not produced much antimatter, so there is nothing to be afraid of.
All the antiprotons created at Fermilab's Tevatron particle accelerator would barely measure 15 nanograms. CERN has only produced about 1 nanogram to date. In DESY in Germany - no more than 2 nanograms of positrons.
If all the antimatter created by humans were annihilated instantly, its energy would not even be enough to boil a cup of tea.
The problem lies in the efficiency and cost of producing and storing antimatter. Creating 1 gram of antimatter requires about 25 million billion kilowatt-hours of energy and costs over a million billion dollars. It is not surprising that antimatter is sometimes included in the list of the ten most expensive substances in our world.
4. There is such a thing as an antimatter trap
To study antimatter, you need to prevent it from annihilating with matter. Scientists have found several ways to do this.
Charged antimatter particles, such as positrons and antiprotons, can be stored in so-called Penning traps. They are like tiny particle accelerators. Inside them, particles move in a spiral while magnetic and electric fields keep them from colliding with the walls of the trap.
However, Penning traps do not work for neutral particles like antihydrogen. Because they have no charge, these particles cannot be confined by electric fields. They are held in Ioffe traps, which work by creating a region of space where the magnetic field becomes stronger in all directions. Antimatter particles get stuck in the region with the weakest magnetic field.
The Earth's magnetic field can act as antimatter traps. Antiprotons were found in certain zones around the Earth - the Van Allen radiation belts.
5. Antimatter can fall (literally)
Matter and antimatter particles have the same mass, but differ in properties such as electric charge and spin. The Standard Model predicts that gravity should affect matter and antimatter equally, but this remains to be seen for sure. Experiments like AEGIS, ALPHA and GBAR are working on this.
Observing the gravitational effect in antimatter is not as easy as watching an apple fall from a tree. These experiments require keeping antimatter trapped or slowing it down by cooling it to temperatures just above absolute zero. And because gravity is the weakest of the fundamental forces, physicists must use neutral antimatter particles in these experiments to prevent interaction with the more powerful force of electricity.
6. Antimatter is being studied in particle moderators
Have you heard of particle accelerators, and have you heard of particle moderators? CERN has a machine called the Antiproton Decelerator, which traps and slows down antiprotons in a ring to study their properties and behavior.
In ring-shaped particle accelerators like the Large Hadron Collider, particles receive an energetic boost each time they complete a circle. Moderators work in the opposite way: instead of accelerating particles, they are pushed in the opposite direction.
7. Neutrinos could be their own antiparticles
A particle of matter and its anti-matter partner carry opposite charges, making them easy to distinguish. Neutrinos, nearly massless particles that rarely interact with matter, have no charge. Scientists think they may be Majorana particles, a hypothetical class of particles that are their own antiparticles.
Projects like the Majorana Demonstrator and EXO-200 aim to determine whether neutrinos are indeed Majorana particles by observing the behavior of so-called neutrinoless double beta decay.
Some radioactive nuclei decay simultaneously, emitting two electrons and two neutrinos. If neutrinos were their own antiparticles, they would annihilate after double decay, leaving scientists with only electrons to observe.
The search for Majorana neutrinos could help explain why matter-antimatter asymmetry exists. Physicists suggest that Majorana neutrinos can be either heavy or light. Light ones exist today, but heavy ones existed right after the Big Bang. Heavy Majorana neutrinos decayed asymmetrically, resulting in the appearance of a tiny amount of matter that filled our Universe.
8. Antimatter is used in medicine
PET, PET (positron emission topography) uses positrons to produce high-resolution images of the body. Positron-emitting radioactive isotopes (like those found in bananas) attach to chemicals like glucose, which are found in the body. They are injected into the bloodstream, where they decay naturally, emitting positrons. Those, in turn, meet with the electrons of the body and annihilate. Annihilation produces gamma rays, which are used to construct images.
Scientists at CERN's ACE Project are studying antimatter as a potential candidate for treating cancer. Doctors have already discovered that they can direct beams of particles at tumors, releasing their energy only after they have safely passed through healthy tissue. The use of antiprotons will add an additional burst of energy. This technique has been found effective for treating hamsters, but has not yet been tested in humans.
9. Antimatter may be lurking in space
One way scientists are trying to solve the problem of matter-antimatter asymmetry is by searching for antimatter left over from the Big Bang.
The Alpha Magnetic Spectrometer (AMS) is a particle detector located on the International Space Station that looks for such particles. The AMS contains magnetic fields that bend the path of cosmic particles and separate matter from antimatter. Its detectors must detect and identify such particles as they pass.
Cosmic ray collisions typically produce positrons and antiprotons, but the likelihood of creating an antihelium atom remains extremely small due to the enormous amount of energy required for this process. This means that the observation of even one antihelium nucleolus would be powerful evidence for the existence of gigantic amounts of antimatter elsewhere in the universe.
10. People are actually studying how to power spacecraft with antimatter fuel.
Just a little bit of antimatter can produce enormous amounts of energy, making it a popular fuel for futuristic ships in science fiction.
Antimatter rocket propulsion is hypothetically possible; the main limitation is collecting enough antimatter for this to happen.
The technology does not yet exist to mass produce or collect antimatter in the quantities required for such applications. However, scientists are working on simulating such movement and storage of this very antimatter. One day, if we find a way to produce large amounts of antimatter, their research could help interstellar travel become a reality. published
The public availability of information of any kind, the abundance of science fiction films, the themes of which are related to certain scientific or pseudoscientific problems, the popularity of sensational novels - all this has led to the formation of a considerable number of myths about our world. For example, thanks to numerous theories that play up variants of the End of the World, the concept of “antimatter” has become widely used. In works of art and apocalyptic theories, antimatter refers to a certain substance whose properties are opposite to substance, matter. A kind of black hole that absorbs and destroys everything that falls into its zone of attraction. What antimatter is, in fact, you need to ask not writers, directors and those obsessed with the expectation of general collapse, but scientists.
Antiparticles and antimatter are a normal part of the universe
Scientists will tell you that there is nothing terrible or catastrophic in antimatter. If only due to the fact that it is impossible to oppose matter and antimatter - what is commonly called antimatter is actually a type of substance, that is, matter. According to scientific classification, particles of matter are usually called material structures consisting of atoms surrounded by elementary particles. The basic part of an atom is the nucleus, which has a positive charge, and the elementary particles around it are negatively charged. These are the same electrons whose name is used by us in everyday life every day when mentioning electronics and electrical appliances.
Antimatter consists of antiparticles, that is, those material structures whose nuclei have a negative charge, and the particles surrounding them have a positive charge.
Positive elementary particles were discovered by scientists only in 1932 and called positrons. There is also no fatal drama in the interaction of particles and antiparticles, matter and antimatter. Annihilation occurs - the process of transformation of reacting matter and antimatter into fundamentally new particles that did not exist initially and have properties different from the original, “mother” particles. True, the “side effect” can be quite dangerous: annihilation is accompanied by the release of a huge amount of energy. It is estimated that the reaction of 1 kilogram of matter with 1 kilogram of antimatter will release energy equal to approximately 43 megatons of exploding TNT. The most powerful nuclear bomb exploded on Earth had a potential of about 58 megatons of TNT.
How to obtain antimatter is not a question for science
The reality of antimatter is a proven fact. The theoretical assumptions of scientists harmoniously combined with the general scientific picture of the world, and then antiparticles were discovered experimentally. For almost fifty years now, antiparticles have been produced artificially through the interaction reaction between particles and antiparticles. In 1965, the anti-deuteron was synthesized, and 30 years later anti-hydrogen was obtained (its difference from “classical” hydrogen is that the antimatter atom consists of a positron and an antiproton). Scientists went further and in 2010-2011 managed to “catch” antimatter atoms in laboratory conditions. Let only about 40 atoms find themselves in the “trap” and they were able to hold them for 172 milliseconds.
The practical prospects for studying antiparticles are obvious, given the enormous energy potential of the interaction of particles and antiparticles.
The use of antimatter and the launch of this process in a controlled manner actually eliminates the problem of obtaining energy once and for all.
The difficulty, as always, is in money: calculations show that today it would cost about 60 trillion dollars to produce just one gram of antimatter. So traditional energy sources remain relevant for now - but research needs to be continued. Moreover, already at the turn of the 20th-21st centuries, astronomers and astrophysicists discovered sources of antimatter in the Universe. In particular, data were obtained on real flows of positively charged elementary particles (positrons) moving in outer space. Several theories, more or less substantiated by practical research, have emerged that explain the mechanisms of the formation of antiparticles in natural conditions.
A very popular explanation is that antiparticles are formed in a strong gravitational field in black holes. This gravitational field interacts with “ordinary” matter, and as a result of the process of “processing” matter, positrons are obtained - particles that, under the influence of gravity, have changed their charge from negative to positive. Another concept points to naturally occurring radioactive elements, the best known of which are supernovae. It is assumed that these natural nuclear reactors “produce” antiparticles as a by-product. There are other versions: for example, the process of merging two stars may be accompanied by the formation of particles with a changed charge or, on the contrary, such an effect may give rise to the death of stars.
Where to find antimatter - a puzzle for researchers
Thus, the presence of antimatter is undeniable. But, as usually happens when studying the secrets of the Universe, a fundamental problem has arisen, which science at this stage of its development has not yet been able to solve. According to the principle of symmetry of the structure of the Universe 
, our world should contain approximately the same amount of matter as antimatter, as many atoms consisting of a positive nucleus and negatively charged particles as atoms with a negative nucleus and positive particles. But in practice, no traces of large-scale accumulations of antimatter (theorists even came up with a name for such accumulations - “antiworld”) have been discovered at the moment.
In astronomical observations, antimatter is detected quite well only due to the emitted gamma radiation. However, optimists do not lose hope – and quite rightly so.
Firstly, the Earth may be located in that “material” part of the Universe that is maximally distant from the “antimatter” half. This means that the whole point is insufficiently powerful and sophisticated observation devices. Secondly, in terms of their electromagnetic radiation, objects consisting of matter and antimatter are indistinguishable, therefore the optical observation method is useless here. Thirdly, compromise theories have not been rejected - for example, that the Universe has a cellular structure, in which each cell consists of half matter and half antimatter.
Alexander Babitsky
