How is Antimatter Made?

Antimatter is the anti-state of normal matter. When the positive and negative matter meet, the two sides will annihilate each other and cancel each other, explode and generate huge energy.

The positrons and negative protons are all anti-particles. Compared with the so-called electrons and protons, they have the same amount of electricity but the opposite polarity. Scientists imagine that there might be matter composed entirely of antiparticles in the universe, which is antimatter.

Electrons and anti-electrons have the same mass but opposite charges. The same goes for protons and antiprotons. So what is the difference between the nature of neutrons and antineutrons? In fact, particle experiments have confirmed that particles and antiparticles have not only opposite charges, but also all other properties that can be opposite. Here we discuss the concept of baryon number.

Protons and neutrons are collectively called nucleons. From the study of nuclear phenomena, people have discovered that protons can be converted into neutrons, and neutrons can also be converted into protons, but the total number of nucleus in the system is constant before and after the conversion. For example, when beta decay occurs, those that emit positrons are called "positive beta decay", and those that emit electrons are called "negative beta decay." In a positive decay, a proton in the nucleus is converted into a neutron, and a positron and a neutrino are released at the same time; in a negative decay, a neutron in the nucleus is converted into a proton, and an electron and an anti- Neutrino. In addition, electron capture is also a type of beta decay, called electron capture beta decay.

Particle experiments since the 1950s show that there are many more particles that are heavier than nucleons. They are also in the same category as nucleons. Such particles are renamed baryons. Nucleons are only their lightest representatives. The general rule is: when Particles are transformed by interaction, and the number of baryons in the system will not change.

Due to the conservation of the number of baryons, the collision of two protons will not produce a system containing three baryons, so how should anti-nucleons be generated? Experiments have shown that antinuclei are always generated in pairs with nucleus during collisions. For example, p + p N + N + N + N '+ several mesons, where N represents a proton or neutron, and N' represents an anti-proton or an anti-neutron. Once an anti-nucleus is generated, it often quickly collides with a surrounding nucleus and annihilates in pairs. E.g

N + N ' several mesons. According to this argument, there must be an antimatter world somewhere in the universe. If the antimatter world does exist, then it can only exist without meeting the matter. How can matter and antimatter not be combined? Where is antimatter in the universe? This is the mystery to be solved.

For baryons heavier than nucleons, the situation is exactly the same. Anti-baryons are always produced in pairs and annihilated in pairs. These experiences make people realize that the conservation law of baryon number needs to be re-understood. People think of the baryon number B as a kind of charge describing the properties of particles. The positive and negative baryons not only have opposite charges, but also have the opposite baryon number B. Let any baryon have B = + 1, then any anti-baryon has B = -1. Non-baryons such as mesons, leptons, and normons do not have baryon numbers, that is, they have B = 0. The conservation law of baryon number can be expressed as: Any particle reaction will not change the total baryon number B of the system. This expression not only reflects the constant number of baryons when anti-particles are not involved, but also summarizes the pairwise generation and annihilation of anti-particles. It is easy to understand the difference between neutrons and antineutrons. They have the opposite number of baryons B, so antineutrons can collide with nucleons and cause annihilation, while neutrons cannot.

In addition, people have similarly found the conservation of lepton numbers. Although neutrinos are not charged and do not have baryon numbers, they have opposite lepton numbers to antineutrinos. According to the conservation of lepton numbers, the physical behavior of neutrinos and antineutrinos is also very different. Experiments also show that the number of mesons and the number of gauge particles are not conserved. In this way, we can see that charge is only one property of particles, and there are other properties that are characterized by physical quantities such as baryon number and lepton number. These properties of the positive and negative particles are also opposite. In 1928, British young physicist Dirac demonstrated the existence of positrons for the first time in theory. This kind of positron has the same properties as the electron except that it is opposite to the electron. In 1932, American physicist Anderson discovered the positron predicted by Dirac in the laboratory. 1955 American physicist

In the view of most theorists, large-scale separation of positive and negative matter in the universe is impossible. Therefore, there is no antimatter celestial body within the range of 30 million light years, which has shown that there is no large antimatter in the universe. But theorists also believe that positive and negative matter in the very early universe should be equal. In this way, what needs to be done is to find the physical mechanism to explain how the universe can transition from the state of positive and negative matter to the state of positive matter. Here, theorists also encountered very acute difficulties.

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The various macroscopic objects in nature are restored to the microscopic origin.

In addition to our common matter, there is antimatter in the universe. Since the British physicist Paul Dirac predicted the existence of antimatter in 1928, antimatter has been the "citron" in the eyes of scientists. Scientists believe that antimatter research

It is of great significance in the aspects of science, universe evolution and so on. An in-depth study of antimatter is an important link to solve the mystery of the origin of the universe.

Antimatter is also the "standard" in many science fiction novels. For example, in the sibling "Angel and Devil" of the movie "The Da Vinci Code", a bomb containing only 0.25 grams of antimatter is enough to wipe the Vatican from the earth; and the "Enterprise" spaceship in the movie "Star Trek" Then use the powerful thrust generated by the matter-antimatter annihilation to obtain super-light speed of flight.

In particle physics, antimatter is a special substance composed of antiparticles. Antiparticles and particles have the same mass but opposite charges and spins. These antiparticles join together to form antimatter. For example, a positron (the antimatter of an electron) and an antiproton can form an antihydrogen atom.

In addition, antimatter has many amazing features. The symmetry magazine website co-founded by Fermi National Laboratory and the Stanford Linear Accelerator Center (SLAC) lists ten things we may not know about antimatter. Thing. ^[7]

Positive and negative material asymmetry

In 1928, Dirac predicted the existence of antiparticles of electrons, positrons.

In 1932, American scientist Carl Anderson accidentally discovered positrons while studying a kind of cosmic rays from distant space, which confirmed Dirac's prediction and caused shock and sensation in the scientific community. Is it accidental or universal? If it is universal, do all other particles have antiparticles? As a result, scientists have added another search target in their research into the microcosm.

In 1936, Anderson won the Nobel Prize in Physics for the year for discovering positrons. Later, antiparticles of other elementary particles were also discovered. In 1955, American researchers created the first antiproton, a proton with a negative charge.

In our universe today, there is a large amount of matter composed of positive particles, but no stable antimatter composed of antiparticles has been found, which indicates that the positive and antimatter in the universe are not strictly symmetrical, otherwise all matter will be annihilated.

The standard theory of the origin of the universe states that matter and antimatter were produced in pairs or equal amounts at the beginning of the Big Bang. When matter and antimatter meet, they annihilate each other, leaving only energy. Therefore, in theory, we should all be non-existent, but this is not the case. The vast majority of leftovers today are positive particles. This is the so-called "positive and antimatter symmetry destruction (symmetry breaking)". In each particle collision test, it was found that the decay of positive particles and antiparticles is slightly different, but the number is still not enough to explain why the antimatter disappears. This is still a big mystery in particle physics. , Scientists have also provided many explanations for this.

Physicists are currently carrying out intensive research, hoping to finally clarify this asymmetry, and perhaps the day when the answer is revealed, it will also kick off a new era of astronomy.

Antimatter is closer to you than you think

A small amount of antimatter continued to land on the earth in the form of cosmic rays and high-energy particles. These antimatter particles reach the atmosphere in the range of 1 to 100 particles per square meter.

But other antimatter sources are just around the corner. For example, bananas also produce antimatter-they emit a positron every 75 minutes. This happens because bananas contain a small amount of potassium-40. Potassium-40 is a natural isotope of potassium that releases positrons during decay.

The body also contains potassium-40, which means that the body also releases positrons. These anti-matter particles are very short-lived because they are annihilated once they come into contact with matter. ^[8]

Expensive but hard to reach

Although the matter-antimatter annihilation has the potential to release a large amount of energy, 1 gram of antimatter may produce an explosion scale equivalent to a nuclear explosion, but humans currently produce very little antimatter.

In 1995, scientists at the European Nuclear Research Center (CERN) created the world s first antimatter, antihydrogen atoms, in the laboratory; in 1996, Fermi National Accelerator Laboratory successfully produced seven antihydrogen atoms. On September 18, 2000, CERN successfully produced about 50,000 anti-hydrogen atoms in a low energy state. This is the first time that humans have produced large quantities of anti-matter under laboratory conditions. In early May 2011, the University of Science and Technology of China cooperated with American scientists to create the heaviest antimatter particle to date-antihelium 4.

However, to date, all of the antiprotons produced by Fermilab's Tevatron accelerators add up to only 15 nanograms (one billionth of a gram); all antiprotons made by CERN add up to only 1 nanogram; positrons made by German electron synchrotron (DESY) add up to about 2 nanograms. Even if all these antimatter are annihilated all at once, the energy they generate is not enough to boil a glass of water.

The fundamental problem lies in the efficiency and cost of manufacturing and storing antimatter. At present, antimatter is generated by high-energy particles produced by accelerators hitting fixed targets to produce antiparticles, which are then synthesized by deceleration. The energy required for this process is far greater than the energy released by annihilation , And the rate of antimatter generation is extremely low: about 25 × 1015 kWh of energy is needed to produce only one gram of antimatter. Therefore, from the perspective of production costs, antimatter is the most expensive substance in the world.

Use "traps" to hold antimatter

Antimatter is also difficult to capture and store. Because antimatter annihilates and explodes as soon as it encounters positive matter, we cannot use any containers made of positive matter to store it, and we must build special "homes" for them.

Charged antimatter particles, such as positrons and antiprotons, can be stored in Penning traps. These devices can be thought of as small accelerators that rely on magnetic and electric fields to keep particles from colliding with the well walls, causing them to spiral. It is reported that scientists from NASA and Pennsylvania State University have been able to use the Penning ion trap to store 1010 antiprotons for a week. However, the Penning ion trap has no effect on anti-hydrogen atoms, etc., because anti-hydrogen atoms are not charged and cannot be "locked" by the electric field. Instead, they are kept in what is commonly known as a "Yap well".

In fact, the Earth's magnetic field is similar to some types of antimatter wells. In 2011, a scientific team in Italy successfully discovered an antiproton band in the Van Allen radiation zone using a cosmic ray detector. The existence area is 350 to 600 kilometers from the earth's surface. This research confirms the theory that the earth's magnetic field can "capture" antiprotons.

Antimatter may fly upwards

Einstein's theory of general relativity tells us that gravity acts equally on any matter; standard model theory also predicts that gravity should have the same effect on matter and antimatter. Then the effect of gravity will make antimatter fall or fly up? If antimatter behaves completely differently, will they upend existing physics theories? CERN's ongoing Aegis (AEGIS) experiment and the Anti-Hydrogen Laser Physics Device (ALPHA) experiment are all trying to discover this.

Of course, observing the effect of gravity on antimatter is not as easy as seeing an apple fall from a tree. These experiments require that antimatter be kept in a trap or cooled down to a temperature above absolute zero to slow it down for better observation. And because gravity is the weakest fundamental force, physicists must use neutral antimatter particles in these experiments to prevent interference from stronger electric fields.

Particle reducer slows down antimatter

Many of us are familiar with particle accelerators, but do you know that particle reducers exist? CERN has a device called the "Antiproton Decelerator". On August 10, 2000, CERN announced that this anti-proton reducer was put into use.

This anti-proton reducer is a circular concrete box with a circumference of 188m and costs $ 11.5 million. It uses a magnetic field to cool, decelerate, and accumulate high-energy antiprotons and positrons, and eventually forms a large number of antihydrogen atoms under the constraint of electromagnetic fields. The temperature of these "cold" antihydrogen atoms is only a few degrees higher than absolute zero. For future research on antiprotons and The properties and behavior of particles such as anti-hydrogen atoms provide the possibility.

In 2014, CERN's "Low-Speed Anti-Proton Atomic Spectroscopy and Collision (ASACUSA)" experimental team mixed positrons with low-energy anti-protons produced by anti-proton reducers to successfully produce anti-hydrogen atom beams for the first time. They detected a 2.7-meter beam of antimatter consisting of 80 anti-hydrogen atoms.

Neutrino or own antiparticle

Matter particles and their antiparticle partners carry opposite charges, making it easy for scientists to distinguish each other. But neutrinos have almost no mass, rarely interact with other substances, and have no charge. Therefore, scientists believe that neutrinos may be Mayorana fermions (the same particles as antiparticles). In the 1930s, Italian physicist Ettorre Mayorana proposed that neutrinos could be their antiparticles.

Mayorana detectors that study neutrino properties and EXO-200 in the U.S. are designed to determine whether a neutrino is a Mayorah by looking for a behavior called neutrino-free double beta decay. Nefermiko. Some radioactive nuclei decay simultaneously, releasing two electrons and two neutrinos. If neutrinos were their own antiparticles, they would annihilate each other instantly after double decay, and scientists would only see electrons.

Finding neutrinos could help scientists explain antimatter-matter asymmetry. Physicists believe that some neutrinos are light and some are heavy. Light neutrinos are present, while heavy neutrinos exist only moments after the Big Bang.

Antimatter "shows its strengths" in the medical field

Even today, although there are not many antimatter particles discovered and manufactured, it is not surprising that antimatter such as positrons. Although it is not yet possible to manufacture and store a large amount of antimatter as described in science fiction, antimatter has been applied on a smaller scale, for example, positron emission computed tomography (PET) equipment used in many hospitals It is the use of positrons to generate high-definition images of the body.

Positron-emitting radioactive isotopes (such as potassium-40 found in bananas) are attached to chemicals such as glucose and then injected into blood vessels together. Glucose breaks down in blood vessels, releasing positrons, which meet the electrons in the body and annihilate each other. This annihilation process generates gamma rays, which can be used to construct an image of the body, thereby providing a diagnostic basis for doctors.

And CERN scientists have been studying antimatter as a potential treatment for cancer. Physicists have discovered that particle beams can be used to attack tumors. These particle beams release energy after safely passing through healthy tissue. Using antiprotons can add another beam of energy. Scientists have found that this technique works on hamster cells, but no relevant studies have yet been performed in humans.

Antimatter after the big bang or still lurking

Scientists have always hoped to "suck out" the antimatter left behind by the Big Bang, thereby solving the mystery of matter-antimatter asymmetry.

The mission of the Alpha Magnetic Spectrometer (AMS-02) on the International Space Station includes searching for these particles. This advanced detector that took off in the Endeavour in 2011 is regarded as a scientific weapon that can make "closing submissions" on antimatter mysteries. In the next ten years, it will explore the existence of antimatter and anti universe in the most ideal place in space. In addition, its mission includes finding dark matter in the universe and exploring cosmic rays.

AMS-02 is the largest magnetic spectrometer sent to space by humans, and can identify an antiparticle from billions of events. This means an improvement of three orders of magnitude over previous experiments. With this accuracy, the detector will detect the composition of the cosmic ray spectrum with unprecedented accuracy.

There is a powerful permanent magnet inside AMS-02. The charged particles and anti-particles will be deflected in opposite directions under the action of them, so that matter and anti-matter will diverge from each other without "seeing each other" and annihilating each other.

Cosmic ray collisions generally produce positrons and antiprotons, but the probability of creating an anti-helium atom is extremely low, as this process requires a lot of energy. This means that even if only one anti-helium nucleus is found, it can be a solid evidence of the existence of a large amount of antimatter somewhere in the universe. These materials were produced after the Big Bang, and their discovery will be a real breakthrough in understanding the universe today.

Antimatter-driven spacecraft still has a long way to go

A potential and very enticing use of antimatter is to make superfuels for interstellar rockets.

Scientists have long discovered that when anti-particles and particles collide and annihilate under high energy, a large amount of energy is released. The release rate of this energy is much higher than that of nuclear bombs and hydrogen bombs, and the energy produced by a few grams is equivalent to a strategic nuclear bomb. Because of this nature, antimatter often appears as fuel for interstellar spacecraft in science fiction. In the "Star Trek" series of movies, the "enterprise" spacecraft can achieve curved flight and reach any place in the universe at the speed of light, relying on its anti-matter dynamic system.

Analysis by Zhang Weiming, a senior researcher at Kent State University in the United States, and Ronan Keenan at the Western Reserve College show that the speed of antimatter rockets can reach 70% of the speed of light. In theory, it is possible to use antimatter as rocket fuel, but before this new idea can be put into practice, people must solve the two problems of scarce antimatter quantity and storage.

At present, scientists still have no way to manufacture or collect enough antimatter on a large scale. After nearly half a century of research, humans can only save antimatter (antihydrogen atoms) at most for 1,000 seconds. According to media reports, in 2011, CERN's scientists successfully held 309 anti-hydrogen atoms to 1,000 seconds, which was 5000 times the previous rate.

However, scientists are a group of people who "know that there are tigers in the mountains, and prefer to travel in the mountains." Many scientists are conducting research on the manufacture and storage of antimatter. If scientists can find a way to make or collect a large amount of antimatter one day in the future, then the interstellar travel promoted by antimatter may come from dream to reality.

But what's interesting is that when anti-matter rockets are actually put into use, passengers must also get used to the so-called relativity effect-when approaching the speed of light, space-time will not move as fast. To put it simply, the journey from Earth to Centaur will take about 6 years for the Earth clock, but it actually feels like less than 4 and a half years have passed.

In fact, the human body also releases antimatter. It is believed that with the continuous development of science and technology and the continuous deepening of scientific research, people's understanding of the role of antimatter will surely become more and more profound, and the antimatter world will certainly contribute to humanity.