Artificially created elements. Why are new chemical elements synthesized? Accessible about complex things. Stages of element synthesis
If you ask scientists which of the discoveries of the 20th century. most important, then hardly anyone will forget to name the artificial synthesis of chemical elements. Behind short term- less than 40 years - list known chemical elements increased by 18 names. And all 18 were synthesized, prepared artificially.
The word "synthesis" usually denotes the process of obtaining from a simple complex. For example, the interaction of sulfur with oxygen is the chemical synthesis of sulfur dioxide SO 2 from elements.
The synthesis of elements can be understood in this way: the artificial production from an element with a lower nuclear charge and a lower atomic number of an element with a higher atomic number. And the process of production itself is called a nuclear reaction. Its equation is written in the same way as the equation of an ordinary chemical reaction. On the left side are the reactants, on the right are the resulting products. The reactants in a nuclear reaction are the target and the bombarding particle.
The target can be any element of the periodic table (in free form or in the form of a chemical compound).
The role of bombarding particles is played by α-particles, neutrons, protons, deuterons (nuclei of the heavy isotope of hydrogen), as well as the so-called multiply charged heavy ions of various elements - boron, carbon, nitrogen, oxygen, neon, argon and other elements of the periodic table.
For a nuclear reaction to occur, the bombarding particle must collide with the nucleus of the target atom. If a particle has a high enough energy, it can penetrate so deeply into the nucleus that it merges with it. Since all the particles listed above, except the neutron, carry positive charges, when they merge with the nucleus, they increase its charge. And a change in the value of Z means the transformation of elements: the synthesis of an element with a new value of the nuclear charge.
To find a way to accelerate bombarding particles and give them high energy, sufficient for them to merge with nuclei, a special particle accelerator, a cyclotron, was invented and constructed. Then they built a special factory for new elements - a nuclear reactor. Its direct purpose is to generate nuclear energy. But since intense neutron fluxes always exist in it, they are easy to use for purposes artificial synthesis. A neutron has no charge, and therefore it does not need (and is impossible) to be accelerated. On the contrary, slow neutrons turn out to be more useful than fast ones.
Chemists had to rack their brains and show real miracles of ingenuity to develop ways to separate tiny amounts of new elements from the target substance. Learn to study the properties of new elements when only a few atoms were available...
Through the work of hundreds and thousands of scientists, eighteen new cells were filled in the periodic table.
Four are within its old boundaries: between hydrogen and uranium.
Fourteen - for uranium.
Here's how it all happened...
Technetium, promethium, astatine, francium... Four places in the periodic table remained empty for a long time. These were cells No. 43, 61, 85 and 87. Of the four elements that were supposed to occupy these places, three were predicted by Mendeleev: ekamanganese - 43, ecaiodine - 85 and ekakaesium - 87. The fourth - No. 61 - was supposed to belong to the rare earth elements .
These four elements were elusive. The efforts of scientists to search for them in nature remained unsuccessful. With the help of the periodic law, all other places in the periodic table - from hydrogen to uranium - have long been filled.
More than once, reports of the discovery of these four elements have appeared in scientific journals. Ekamanganese was "discovered" in Japan, where it was given the name "nipponium", and in Germany it was called "masurium". Element No. 61 was "discovered" in different countries at least three times, he received the names “Illinium”, “Florence”, “Cycle Onium”. Ekaiodine has also been found in nature more than once. He was given the names "Alabamius", "Helvetius". Ekacesium, in turn, received the names of “Virginia” and “Moldova”. Some of these names found their way into various reference books and even found their way into school textbooks. But all these discoveries were not confirmed: each time an accurate check showed that an error had been made, and random insignificant impurities were mistaken for a new element.
A long and difficult search finally led to the discovery of one of nature's elusive elements. It turned out that excasium, which should occupy 87th place in the periodic table, arises in the decay chain of the natural radioactive isotope uranium-235. It is a short-lived radioactive element.
Element No. 87 deserves to be discussed in more detail.
Now in any encyclopedia, in any chemistry textbook we read: francium (serial number 87) was discovered in 1939 by the French scientist Margarita Perey. By the way, this is the third time that the honor of discovering a new element belongs to a woman (previously, Marie Curie discovered polonium and radium, Ida Noddak discovered rhenium).
How did Perey manage to capture the elusive element? Let's go back many years. In 1914, three Austrian radiochemists - S. Meyer, W. Hess and F. Paneth - began studying the radioactive decay of the actinium isotope with mass number 227. It was known that it belongs to the actinouranium family and emits β-particles; hence its breakdown product is thorium. However, scientists had vague suspicions that actinium-227 in rare cases also emits α particles. In other words, this is one example of a radioactive fork. It is easy to figure out: during such a transformation, an isotope of element No. 87 should be formed. Meyer and his colleagues did indeed observe alpha particles. Further research was required, but it was interrupted by the First World War.
Margarita Perey followed the same path. But she had more sensitive instruments and new, improved methods of analysis at her disposal. That's why she was successful.
Francium is classified as an artificially synthesized element. But still, the element was first discovered in nature. This is an isotope of francium-223. Its half-life is only 22 minutes. It becomes clear why there is so little France on Earth. Firstly, due to its fragility, it does not have time to concentrate in any noticeable quantities, and secondly, the process of its formation itself is characterized by a low probability: only 1.2% of actinium-227 nuclei decay with the emission of α-particles.
In this regard, it is more profitable to prepare francium artificially. 20 isotopes of francium have already been obtained, and the longest-lived of them is francium-223. Working with absolutely insignificant amounts of francium salts, chemists were able to prove that its properties are extremely similar to cesium.
Elements No. 43, 61 and 85 remained elusive. They could not be found in nature, although scientists already possessed a powerful method that unmistakably showed the way to search for new elements - the periodic law. Thanks to this law, all the chemical properties of an unknown element were known to scientists in advance. So why were the searches for these three elements in nature unsuccessful?
Studying the properties of atomic nuclei, physicists came to the conclusion that elements with atomic numbers 43, 61, 85 and 87 cannot exist. stable isotopes. They can only be radioactive, have short half-lives and must disappear quickly. Therefore, all these elements were created artificially by man. The paths for the creation of new elements were indicated by the periodic law. Let's try to use it to outline the path for the synthesis of ecamanganese. This element No. 43 was the first artificially created.
The chemical properties of an element are determined by its electron shell, and it depends on the charge of the atomic nucleus. The nucleus of element number 43 should have 43 positive charges and 43 electrons orbiting the nucleus. How can you create an element with 43 charges in the atomic nucleus? How can you prove that such an element has been created?
Let's take a closer look at which elements in the periodic table are located near the empty space intended for element No. 43. It is located almost in the middle of the fifth period. In the corresponding places in the fourth period there is manganese, and in the sixth - rhenium. Therefore, the chemical properties of element 43 should be similar to those of manganese and rhenium. It is not for nothing that D.I. Mendeleev, who predicted this element, called it ekamanganese. To the left of the 43rd cell is molybdenum, which occupies cell 42, to the right, in the 44th, is ruthenium.
Therefore, to create element number 43, it is necessary to increase the number of charges in the nucleus of an atom that has 42 charges by one more elementary charge. Therefore, to synthesize the new element No. 43, it is necessary to take molybdenum as the starting material. It has exactly 42 charges in its core. One positive charge The lightest element is hydrogen. So, we can expect that element number 43 can be obtained from a nuclear reaction between molybdenum and hydrogen.
The properties of element No. 43 should be similar to the chemical properties of manganese and rhenium, and in order to detect and prove the formation of this element, one must use chemical reactions, similar to those with which chemists determine the presence of small quantities of manganese and rhenium. This is how the periodic table makes it possible to chart the path for the creation of an artificial element.
In exactly the same way that we have just outlined, the first artificial chemical element was created in 1937. It received a significant name - technetium - the first element produced technically, artificially. This is how technetium was synthesized. The molybdenum plate was subjected to intense bombardment by nuclei of the heavy isotope of hydrogen - deuterium, which were accelerated in a cyclotron to enormous speed.
Heavy hydrogen nuclei, which received very high energy, penetrated into the molybdenum nuclei. After irradiation in a cyclotron, the molybdenum plate was dissolved in acid. An insignificant amount of a new radioactive substance was isolated from the solution using the same reactions that are necessary for the analytical determination of manganese (an analogue of element No. 43). This was the new element - technetium. Soon its chemical properties were studied in detail. They correspond exactly to the position of the element in the periodic table.
Now technetium has become quite accessible: it is formed in fairly large quantities in nuclear reactors. Technetium has been well studied and is already in practical use. Technetium is used to study the corrosion process of metals.
The method by which element 61 was created is very similar to the method by which technetium is obtained. Element #61 must be a rare earth element: the 61st cell is between neodymium (#60) and samarium (#62). The new element was first obtained in 1938 in a cyclotron by bombarding neodymium with deuterium nuclei. Chemically, element 61 was isolated only in 1945 from fragmentation elements formed in a nuclear reactor as a result of the fission of uranium.
The element received the symbolic name promethium. This name was given to him for a reason. An ancient Greek myth tells that the titan Prometheus stole fire from the sky and gave it to people. For this he was punished by the gods: he was chained to a rock, and a huge eagle tormented him every day. The name “promethium” not only symbolizes the dramatic path of science stealing the energy of nuclear fission from nature and mastering this energy, but also warns people against a terrible military danger.
Promethium is now produced in considerable quantities: it is used in atomic battery sources direct current, capable of operating without interruption for several years.
The heaviest halide element No. 85 was synthesized in a similar way. It was first obtained by bombarding bismuth (No. 83) with helium nuclei (No. 2), accelerated in a cyclotron to high energies.
The nuclei of helium, the second element in the periodic table, have two charges. Therefore, to synthesize the 85th element, bismuth was taken - the 83rd element. The new element is named astatine (unstable). It is radioactive and disappears quickly. Its chemical properties also turned out to be exactly the same periodic law. It looks like iodine.
Transuranic elements.
Chemists put a lot of work into searching for elements heavier than uranium in nature. More than once triumphant notices have appeared in scientific journals about the “reliable” discovery of a new “heavy” element with an atomic mass greater than that of uranium. For example, element No. 93 was “discovered” in nature many times, it received the names “bohemia” and “sequanium”. But these “discoveries” turned out to be the result of mistakes. They characterize the difficulty of accurately analytically determining minute traces of a new unknown element with unstudied properties.
The result of these searches was negative, because there are practically no elements on Earth corresponding to those cells of the periodic table that should be located beyond the 92nd cell.
The first attempts to artificially obtain new elements heavier than uranium are associated with one of the remarkable mistakes in the history of the development of science. It was noticed that under the influence of a neutron flux, many elements become radioactive and begin to emit beta rays. The nucleus of an atom having lost negative charge, shifts in the periodic table one cell to the right, and its serial number becomes one more - a transformation of elements occurs. Thus, under the influence of neutrons, more heavy elements.
They tried to influence uranium with neutrons. Scientists hoped that, just like other elements, uranium would exhibit β-activity and, as a result of β-decay, a new element with a number one higher would appear. He will occupy the 93rd cell in the Mendeleev system. It was suggested that this element should be similar to rhenium, so it was previously called ekarenium.
The first experiments seemed to immediately confirm this assumption. Even more, it was discovered that in this case not one new element arises, but several. Five new elements heavier than uranium have been reported. In addition to ekarenium, ecaosmium, ecairidium, ekaplatinum and ecagold were “discovered”. And all the discoveries turned out to be a mistake. But it was a remarkable mistake. She led science to the greatest achievement of physics in the entire history of mankind - the discovery of the fission of uranium and the mastery of the energy of the atomic nucleus.
No transuranium elements have actually been found. In the strange new elements they tried in vain to find the supposed properties that the elements from ekarenium and ekazold should have had. And suddenly, among these elements, radioactive barium and lanthanum were unexpectedly discovered. Not transuranium, but the most common, but radioactive isotopes of elements whose places are in the middle of Mendeleev’s periodic table.
A little time passed before this unexpected and very strange result was correctly understood.
Why do the atomic nuclei of uranium, which is at the end of the periodic system of elements, form under the action of neutrons the nuclei of elements whose places are in its middle? For example, when neutrons act on uranium, elements appear that correspond to the following cells of the periodic table:
Many elements were found in an unimaginably complex mixture radioactive isotopes, formed in uranium irradiated with neutrons. Although they turned out to be old elements long known to chemists, at the same time they were new substances, first created by man.
In nature there are no radioactive isotopes of bromine, krypton, strontium and many other of the thirty-four elements - from zinc to gadolinium, which arise when uranium is irradiated.
This often happens in science: the most mysterious and the most complex turns out to be simple and clear when it is solved and understood. When a neutron hits a uranium nucleus, it splits, splitting into two fragments - into two atomic nuclei of smaller mass. These fragments can be of different sizes, which is why so many different radioactive isotopes of common chemical elements are formed.
One atomic nucleus of uranium (92) decays into atomic nuclei bromine (35) and lanthanum (57), fragments during the splitting of the other may turn out to be the atomic nuclei of krypton (36) and barium (56). The sum of the atomic numbers of the resulting fragmentation elements will be equal to 92.
This was the beginning of a chain of great discoveries. It was soon discovered that under the impact of a neutron, not only fragments - nuclei with a smaller mass - arise from the nucleus of a uranium-235 atom, but also two or three neutrons fly out. Each of them, in turn, is capable of again causing fission of the uranium nucleus. And with each such division, a lot of energy is released. This was the beginning of man's mastery of intra-atomic energy.
Among the huge variety of products arising from the irradiation of uranium nuclei with neutrons, the first true transuranium element No. 93, which had remained unnoticed for a long time, was subsequently discovered. It arose from the action of neutrons on uranium-238. In terms of chemical properties, it turned out to be very similar to uranium and was not at all similar: to rhenium, as was expected during the first attempts to synthesize elements heavier than uranium. Therefore, they could not immediately detect him.
The first element created by man outside the “natural system of chemical elements” was named neptunium after the planet Neptune. Its creation expanded for us the boundaries defined by nature itself. Likewise, the predicted discovery of the planet Neptune expanded the boundaries of our knowledge of the solar system.
Soon the 94th element was synthesized. It was named after the last planet. solar system.
It was called plutonium. In the periodic table of Mendeleev, it follows neptunium in order, similarly to " last planet Solar* system to Pluto, whose orbit lies beyond the orbit of Neptune. Element No. 94 arises from neptunium during its β decay.
Plutonium is the only transuranium element that is now produced in nuclear reactors in very large quantities. Like uranium-235, it is capable of fission under the influence of neutrons and is used as fuel in nuclear reactors.
Elements No. 95 and No. 96 are called americium and curium. They are also now produced in nuclear reactors. Both elements have very high radioactivity - they emit α-rays. The radioactivity of these elements is so great that concentrated solutions of their salts heat up, boil and glow very strongly in the dark.
All transuranium elements - from neptunium to americium and curium - were obtained in fairly large quantities. In their pure form, these are silver-colored metals, they are all radioactive and their chemical properties are somewhat similar to each other, but in some ways they differ noticeably.
The 97th element, berkelium, was also isolated in its pure form. To do this, it was necessary to place a pure plutonium preparation inside a nuclear reactor, where it was exposed to a powerful flow of neutrons for six whole years. During this time, several micrograms of element No. 97 accumulated in it. Plutonium was removed from the nuclear reactor, dissolved in acid, and the longest-lived berkelium-249 was isolated from the mixture. It is highly radioactive - it decays by half in a year. So far, only a few micrograms of berkelium have been obtained. But this amount was enough for scientists to accurately study its chemical properties.
A very interesting element is number 98 - californium, the sixth after uranium. Californium was first created by bombarding a curium target with alpha particles.
The story of the synthesis of the next two transuranium elements: 99 and 100 is fascinating. They were first found in clouds and "mud". To study what is produced in thermonuclear explosions, an airplane flew through the explosion cloud and samples of the sediment were collected on paper filters. Traces of two new elements were found in this sediment. To obtain more accurate data, a large amount of “dirt” - soil and rock altered by the explosion - was collected at the explosion site. This “dirt” was processed in the laboratory, and two new elements were isolated from it. They were named einsteinium and fermium, in honor of the scientists A. Einstein and E. Fermi, to whom humanity primarily owes the discovery of ways to master atomic energy. Einstein came up with the law of equivalence of mass and energy, and Fermi built the first atomic reactor. Now einsteinium and fermium are also produced in laboratories.
Elements of the second hundred.
Not so long ago, hardly anyone could believe that the symbol of the hundredth element would be included in the periodic table.
The artificial synthesis of elements did its job: for a short time, fermium closed the list of known chemical elements. The thoughts of the scientists were now directed into the distance, to the elements of the second hundred.
But there was a barrier along the way that was not easy to overcome.
Until now, physicists have synthesized new transuranium elements mainly in two ways. Or they fired at targets made of transuranium elements, already synthesized, with alpha particles and deuterons. Or they bombarded uranium or plutonium with powerful streams of neutrons. As a result, very neutron-rich isotopes of these elements were formed, which, after several successive β-decays, turned into isotopes of new transuraniums.
However, in the mid-50s, both of these possibilities had exhausted themselves. In nuclear reactions, it was possible to obtain weightless amounts of einsteinium and fermium, and therefore targets could not be made from them. The neutron synthesis method also did not allow progress beyond fermium, since isotopes of this element were subject to spontaneous fission with a much higher probability than beta decay. It is clear that under such conditions it made no sense to talk about the synthesis of a new element.
Therefore, physicists took the next step only when they managed to accumulate the minimum amount of element No. 99 required for the target. This happened in 1955.
One of the most remarkable achievements that science can rightly be proud of is the creation of the 101st element.
This element was named after the great creator of the periodic system of chemical elements, Dmitry Ivanovich Mendeleev.
Mendelevium was obtained as follows. An invisible coating consisting of approximately one billion einsteinium atoms was applied to a piece of the thinnest gold foil. Alpha particles with very high energy, breaking through gold foil with reverse side, upon collision with einsteinium atoms could enter into a nuclear reaction. As a result, atoms of the 101st element were formed. With such a collision, mendelevium atoms flew out from the surface of the gold foil and collected on another, nearby thin gold leaf. In this ingenious way, it was possible to isolate pure atoms of element 101 from a complex mixture of einsteinium and its decay products. The invisible plaque was washed off with acid and subjected to radiochemical research.
Truly it was a miracle. The starting material for the creation of element 101 in each individual experiment was approximately one billion einsteinium atoms. This is very little less than one billionth of a milligram, and it was impossible to obtain einsteinium in larger quantities. It was calculated in advance that out of a billion einsteinium atoms, during many hours of bombardment with alpha particles, only one single einsteinium atom can react and, therefore, only one atom of a new element can be formed. It was necessary not only to be able to detect it, but also to do it in such a way as to determine the chemical nature of the element from just one atom.
And it was done. The success of the experiment exceeded calculations and expectations. It was possible to notice in one experiment not one, but even two atoms of the new element. In total, seventeen mendelevium atoms were obtained in the first series of experiments. This turned out to be enough to establish the fact of the formation of a new element, its place in the periodic table, and determine its basic chemical and radioactive properties. It turned out that this is an α-active element with a half-life of about half an hour.
Mendelevium, the first element of the second hundred, turned out to be a kind of milestone on the path to the synthesis of transuranium elements. Until now, it remains the last of those that were synthesized using old methods - irradiation with α-particles. Now more powerful projectiles have come onto the scene - accelerated multi-charged ions of various elements. Determination of the chemical nature of mendelevium from a few of its atoms marked the beginning of a completely new scientific discipline- physical chemistry of single atoms.
The symbol of element No. 102 No - in the periodic table is placed in brackets. And in these brackets there is a long and complicated story this element.
The synthesis of Nobelium was reported in 1957 by an international group of physicists working at the Nobel Institute (Stockholm). For the first time, heavy accelerated ions were used to synthesize a new element. They were 13 C ions, the flow of which was directed to the curium target. The researchers concluded that they had succeeded in synthesizing the isotope of element 102. It was named after the founder of the Nobel Institute and the inventor of dynamite, Alfred Nobel.
A year passed, and the experiments of the Stockholm physicists were reproduced almost simultaneously in the Soviet Union and the USA. And it turned out amazing thing: the results of Soviet and American scientists had nothing in common either with the work of the Nobel Institute or with each other. No one else has been able to repeat the experiments conducted in Sweden. This situation gave rise to a rather sad joke: “Nobel is all that’s left” (No means “no” in English). The symbol hastily placed on the periodic table did not reflect the actual discovery of the element.
A reliable synthesis of element No. 102 was carried out by a group of physicists from the Laboratory of Nuclear Reactions of the Joint Institute nuclear research. In 1962-1967. Soviet scientists synthesized several isotopes of element No. 102 and studied its properties. Confirmation of these data was received in the USA. However, the No symbol, without having any right to do so, is still in the 102nd cell of the table.
Lawrence, element number 103 with the symbol Lw, named after the inventor of the cyclotron, E. Lawrence, was synthesized in 1961 in the USA. But the merit of Soviet physicists is no less important here. They obtained several new isotopes of lawrencium and studied the properties of this element for the first time. Lawrencium also came into being through the use of heavy ions. The californium target was irradiated with boron ions (or the americium target with oxygen ions).
Element No. 104 was first obtained by Soviet physicists in 1964. Its synthesis was achieved by bombarding plutonium with neon ions. The 104th element was named kurchatovium (symbol Ki) in honor of the outstanding Soviet physicist Igor Vasilyevich Kurchatov.
The 105th and 106th elements were also synthesized for the first time by Soviet scientists - in 1970 and 1974. The first of them, a product of bombardment of americium with neon ions, was named nielsborium (Ns) in honor of Niels Bohr. The synthesis of the other was carried out as follows: a lead target was bombarded with chromium ions. Syntheses of elements 105 and 106 were also carried out in the USA.
You will learn about this in the next chapter, and we will conclude this one a short story About,
How to study the properties of the elements of the second hundred.
A fantastically difficult task faces experimenters.
Here are its initial conditions: given a few quantities (tens, at best hundreds) of atoms of a new element, and very short-lived atoms (half-lives are measured in seconds, or even fractions of a second). It is required to prove that these atoms are atoms of a truly new element (that is, determine the value of Z, as well as the value of the mass number A in order to know which isotope of the new transuranium we are talking about), and study its most important chemical properties.
A few atoms, an insignificant life expectancy...
Speed and the highest ingenuity come to the aid of scientists. But a modern researcher - a specialist in the synthesis of new elements - must not only be able to “shoe a flea.” He must also be fluent in theory.
Let us follow the basic steps by which a new element is identified.
The most important business card primarily radioactive properties - this can be the emission of α-particles or spontaneous fission. Each α-active nucleus is characterized by specific energy values of α-particles. This circumstance allows one to either identify known nuclei or conclude that new ones have been discovered. For example, by studying the characteristics of α-particles, scientists were able to obtain reliable evidence of the synthesis of the 102nd and 103rd elements.
Energetic fragment nuclei resulting from fission are much easier to detect than alpha particles due to the much higher energy of the fragments. To register them, plates made of a special type of glass are used. The fragments leave slightly noticeable marks on the surface of the records. The plates then undergo chemical treatment (etching) and are carefully examined under a microscope. Glass dissolves in hydrofluoric acid.
If a glass plate shelled with fragments is placed in a solution of hydrofluoric acid, then in the places where the fragments hit, the glass will dissolve faster and holes will form there. Their sizes are hundreds of times larger than the original trace left by the fragment. The wells can be observed under a microscope with low magnification. Other radioactive radiation cause less damage to the glass surface and are not visible after etching.
Here is what the authors of the Kurchatov synthesis say about how the process of identifying a new element took place: “The experiment is underway. For forty hours, neon nuclei continuously bombard the plutonium target. For forty hours, the tape carries synthetic nuclei to the glass plates. Finally, the cyclotron is turned off. The glass plates are transferred to the laboratory for processing We are looking forward to the result. Several hours pass. Six tracks were detected from their position. The half-life was calculated to be in the time interval from 0.1 to 0.5 s.
And here is how the same researchers talk about assessing the chemical nature of kurchatovium and nilsborium. "The scheme for studying the chemical properties of element No. 104 is as follows. Recoil atoms exit the target into a stream of nitrogen, are inhibited in it, and then are chlorinated. Compounds of the 104th element with chlorine easily penetrate through a special filter, but all actinides do not pass through. If the 104th belonged to the actinide series, then it would have been retained by the filter. However, studies have shown that the 104th element is a chemical analogue of hafnium. This is the most important step towards filling the periodic table with new elements.
Then the chemical properties of element 105 were studied in Dubna. It turned out that its chlorides are adsorbed on the surface of the tube along which they move from the target at a temperature lower than hafnium chlorides, but higher than niobium chlorides. Only atoms of an element similar in chemical properties to tantalum could behave this way. Look at the periodic table: a chemical analogue of tantalum - element No. 105! Therefore, experiments on adsorption on the surface of atoms of the 105th element confirmed that its properties coincide with those predicted on the basis of the periodic table."
Of the 26 currently known transuranium elements, 24 are not found on our planet. They were created by man. How are heavy and superheavy elements synthesized?
The first list of thirty-three putative elements, A Table of Substances belonging to all the Kingdoms of Nature, which may be considered the Simplest Constituents of Bodies, was published by Antoine Laurent Lavoisier in 1789. Along with oxygen, nitrogen, hydrogen, seventeen metals and several other real elements, light, caloric and some oxides appeared in it. And when 80 years later Mendeleev came up with the Periodic Table, chemists knew 62 elements. By the beginning of the 20th century, it was believed that 92 elements existed in nature - from hydrogen to uranium, although some of them had not yet been discovered. However, already in late XIX centuries, scientists assumed the existence of elements following uranium in the periodic table (transuranes), but they could not be detected. It is now known that in earth's crust contains trace amounts of elements 93 and 94 - neptunium and plutonium. But historically, these elements were first obtained artificially and only then discovered in the composition of minerals.
Of the 94 first elements, 83 have either stable or long-lived isotopes, the half-lives of which are comparable to the age of the Solar System (they came to our planet from a protoplanetary cloud). The life of the remaining 11 natural elements is much shorter, and therefore they appear in the earth’s crust only as a result of radioactive decay for a short time. But what about all the other elements, from 95 to 118? There are none on our planet. All of them were obtained artificially.
The first artificial
The creation of artificial elements has a long history. The fundamental possibility of this became clear in 1932, when Werner Heisenberg and Dmitry Ivanenko came to the conclusion that atomic nuclei consist of protons and neutrons. Two years later, Enrico Fermi's group attempted to produce transuraniums by irradiating uranium with slow neutrons. It was assumed that the uranium nucleus would capture one or two neutrons, after which it would undergo beta decay to produce elements 93 or 94. They even hastened to announce the discovery of transurans, which Fermi called ausonium and hesperium in his Nobel speech in 1938. However, German radiochemists Otto Hahn and Fritz Strassmann, together with the Austrian physicist Lise Meitner, soon showed that Fermi was mistaken: these nuclides were isotopes of already known elements, resulting from the splitting of uranium nuclei into pairs of fragments of approximately the same mass. It was this discovery, made in December 1938, that made it possible to create a nuclear reactor and atomic bomb The first element synthesized was not transuranium at all, but ecamanganese, predicted by Mendeleev. They searched for it in various ores, but to no avail. And in 1937, ecamanganese, later called technetium (from the Greek ??? - artificial) was obtained by firing deuterium nuclei at a molybdenum target, accelerated in a cyclotron at the Lawrence Berkeley National Laboratory.
Light projectiles
Elements 93 to 101 were obtained by the interaction of uranium nuclei or subsequent transuranium nuclei with neutrons, deuterons (deuterium nuclei) or alpha particles (helium nuclei). The first success here was achieved by the Americans Edwin McMillan and Philip Abelson, who in 1940 synthesized neptunium-239, working on Fermi’s idea: the capture of slow neutrons by uranium-238 and the subsequent beta decay of uranium-239. The next, 94th element - plutonium - was discovered for the first time while studying the beta decay of neptunium-238 obtained by deuteron bombardment of uranium at a cyclotron University of California in Berkeley in early 1941. And it soon became clear that plutonium-239, under the influence of slow neutrons, is fissile no worse than uranium-235 and can serve as the filling of an atomic bomb. Therefore, all information about the production and properties of this element was classified, and the article by MacMillan, Glenn Seaborg (for their discoveries they shared Nobel Prize 1951) and their colleagues with a message about the second transuranium appeared in print only in 1946. American authorities also delayed the publication of the discovery of the 95th element, americium, which at the end of 1944 was isolated by Seaborg’s group from the products of neutron bombardment for almost six years plutonium in a nuclear reactor. A few months earlier, physicists from the same team obtained the first isotope of element 96 with an atomic weight of 242, synthesized by bombarding uranium-239 with accelerated alpha particles. It was named curium in recognition of the scientific achievements of Pierre and Marie Curie, thereby opening the tradition of naming transurans in honor of the classics of physics and chemistry. The 60-inch cyclotron at the University of California became the site of the creation of three more elements, 97, 98 and 101 . The first two were named after their place of birth - berkelium and californium. Berkeley was synthesized in December 1949 by bombarding an americium target with alpha particles, and californium two months later by the same bombardment of curium. The 99th and 100th elements, einsteinium and fermium, were discovered during radiochemical analysis of samples collected in the area of \u200b\u200bEniwetak Atoll, where on November 1, 1952, the Americans detonated a ten-megaton thermonuclear charge "Mike", the shell of which was made of uranium-238. During the explosion, uranium nuclei absorbed up to fifteen neutrons, after which they underwent chains of beta decays, which led to the formation of these elements. Element 101, mendelevium, was discovered in early 1955. Seaborg, Albert Ghiorso, Bernard Harvey, Gregory Choppin and Stanley Thomson subjected alpha particle bombardment to about a billion (this is very small, but there were simply no more) einsteinium atoms electrolytically deposited on gold foil. Despite the extremely high beam density (60 trillion alpha particles per second), only 17 mendelevium atoms were obtained, but their radiation and chemical properties were determined.
Heavy ions
Mendelevium was the last transuranium produced using neutrons, deuterons or alpha particles. To obtain the following elements, targets were required from element number 100 - fermium, which were then impossible to manufacture (even now in nuclear reactors fermium is obtained in nanogram quantities). Scientists took a different route: they used ionized atoms, whose nuclei contain more than two protons, to bombard targets. they are called heavy ions). To accelerate ion beams, specialized accelerators were required. The first such machine, HILAC (Heavy Ion Linear Accelerator), was launched in Berkeley in 1957, the second, the U-300 cyclotron, was launched at the Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna in 1960. Later, more powerful U-400 and U-400M units were put into operation in Dubna. Another UNILAC (Universal Linear Accelerator) accelerator has been operating at the German Helmholtz Center for Heavy Ion Research in Wickhausen, one of the Darmstadt districts, since the end of 1975. During the bombardment of targets made of lead, bismuth, uranium or transuranium with heavy ions, highly excited ( hot) nuclei that either fall apart or release excess energy through the emission (evaporation) of neutrons. Sometimes these nuclei emit one or two neutrons, after which they undergo other transformations - for example, alpha decay. This type of synthesis is called cold. In Darmstadt, with its help, elements with numbers from 107 (borium) to 112 (copernicium) were obtained. In the same way, in 2004, Japanese physicists created one atom of the 113th element (a year earlier it was obtained in Dubna). During hot fusion, newborn nuclei lose more neutrons - from three to five. In this way, Berkeley and Dubna synthesized elements from 102 (nobelium) to 106 (seaborgium, in honor of Glenn Seaborg, under whose leadership nine new elements were created). Later, in Dubna, six of the most massive super-heavyweights were made in this way - from the 113th to the 118th. The International Union of Pure and Applied Chemistry (IUPAC) has so far only approved the names of the 114th (flerovium) and 116th (livermorium) elements.
Just three atoms
The 118th element with the temporary name ununoctium and the symbol Uuo (according to IUPAC rules, temporary names of elements are formed from the Latin and Greek roots of the names of the digits of their atomic number, un-un-oct (ium) - 118) was created by the joint efforts of two scientific groups: Dubna under the leadership of Yuri Oganesyan and the Livermore National Laboratory under the leadership of Kenton Moody, a student of Seaborg. Ununoctium is located below radon in the periodic table and may therefore be a noble gas. However, its chemical properties have not yet been determined, since physicists have created only three atoms of this element with a mass number of 294 (118 protons, 176 neutrons) and a half-life of about a millisecond: two in 2002 and one in 2005. They were obtained by bombarding a target of California-249 (98 protons, 151 neutrons) with ions of the heavy isotope of calcium with an atomic mass of 48 (20 protons and 28 neutrons), accelerated in the U-400 accelerator. Total number calcium “bullets” amounted to 4.1x1019, so the productivity of the Dubna “ununoctium generator” is extremely low. However, according to Kenton Moody, the U-400 is the only machine in the world on which it was possible to synthesize the 118th element. “Each series of experiments on the synthesis of transuraniums adds new information about the structure of nuclear matter, which is used to model the properties superheavy nuclei. In particular, work on the synthesis of the 118th element made it possible to discard several previous models, recalls Kenton Moody. - We made the target from californium, since heavier elements were not available in the required quantities. Calcium-48 contains eight extra neutrons compared to its main isotope calcium-40. When its nucleus fused with the californium nucleus, nuclei with 179 neutrons were formed. They were in highly excited and therefore particularly unstable states, from which they quickly emerged, shedding neutrons. As a result, we obtained an isotope of element 118 with 176 neutrons. And these were real neutral atoms with a full set of electrons! If they had lived a little longer, one would have been able to judge their chemical properties».
Methuselah number 117
Element 117, also known as ununseptium, was obtained later - in March 2010. This element was created on the same U-400 machine, where, as before, calcium-48 ions were fired at a target made of berkelium-249, synthesized at the Oak Ridge National Laboratory. When berkelium and calcium nuclei collided, highly excited ununseptium-297 nuclei (117 protons and 180 neutrons) appeared. The experimenters managed to obtain six nuclei, five of which evaporated four neutrons each and turned into ununseptium-293, and the rest emitted three neutrons and gave rise to ununseptium-294. In comparison with ununoctium, ununseptium turned out to be a real Methuselah. The half-life of the lighter isotope is 14 milliseconds, and the heavier one is as much as 78 milliseconds! In 2012, Dubna physicists obtained five more atoms of ununseptium-293, and later several atoms of both isotopes. In the spring of 2014, scientists from Darmstadt reported the synthesis of four nuclei of element 117, two of which had an atomic mass of 294. The half-life of this “heavy” ununseptium, measured by German scientists, was about 51 milliseconds (this agrees well with the estimates of scientists from Dubna) Now in Darmstadt they are preparing a project for a new linear accelerator of heavy ions on superconducting magnets, which will allow the synthesis of elements 119 and 120. Similar plans are being implemented in Dubna, where a new cyclotron DS-280 is being built. It is possible that in just a few years the synthesis of new superheavy transuraniums will become possible. And the creation of the 120th, or even the 126th element with 184 neutrons and the discovery of the island of stability will become a reality.
Long life on the island of stability
Inside nuclei there are proton and neutron shells, somewhat similar to the electron shells of atoms. Nuclei with completely filled shells are especially resistant to spontaneous transformations. The numbers of neutrons and protons corresponding to such shells are called magic. Some of them have been determined experimentally - these are 2, 8, 20 and 28.Shell models make it possible to calculate the “magic numbers” of superheavy nuclei theoretically - however, without a complete guarantee. There is reason to expect that the neutron number 184 will be magical. It can correspond to proton numbers 114, 120 and 126, and the latter, again, must be magical. If this is so, then the isotopes of the 114th, 120th and 126th elements, containing 184 neutrons each, will live much longer than their neighbors on the periodic table - minutes, hours, or even years (this area of the table is usually called the island of stability ). Scientists place their greatest hopes on the last isotope with a doubly magic nucleus.
Dubninsky method
When a heavy ion enters the area nuclear forces the target can form a compound nucleus in an excited state. It either breaks into fragments approximately equal mass, or emits (evaporates) several neutrons and goes into the ground (unexcited) state.
“Elements 113 to 118 were created based on a remarkable method developed in Dubna under the leadership of Yuri Oganesyan,” explains Darmstadt team member Alexander Yakushev. - Instead of nickel and zinc, which were used to fire at targets in Darmstadt, Oganesyan took an isotope with a much lower atomic mass - calcium-48. The fact is that the use of light nuclei increases the likelihood of their fusion with target nuclei. The calcium-48 nucleus is also doubly magical, since it is composed of 20 protons and 28 neutrons. Therefore, Oganesyan's choice greatly contributed to the survival of the compound nuclei that arise when the target is fired upon. After all, a nucleus can shed several neutrons and give rise to a new transuranium only if it does not fall apart into fragments immediately after birth. To synthesize superheavy elements in this way, Dubna physicists made targets from transuranium produced in the USA - first plutonium, then americium, curium, californium and, finally, berkelium. Calcium-48 in nature is only 0.7%. It is extracted using electromagnetic separators, which is an expensive procedure. One milligram of this isotope costs about $200. This amount is enough for an hour or two of shelling a target, and experiments last for months. The targets themselves are even more expensive, their price reaches a million dollars. Paying electricity bills also costs a pretty penny - heavy ion accelerators consume megawatts of power. In general, the synthesis of superheavy elements is not a cheap pleasure.”
Synthesis of elements
Back in the early 40s, they tried to use the idea of the Big Bang to explain the origin of chemical elements. American researchers R. Alpher, G. Gamow and R. Herman suggested that at the earliest stages of its existence the Universe was a clump of super-dense neutron gas (or, as they called it, “ilema”). Later, however, it was shown that a number of heavy elements could be formed in the interior of stars due to cycles of nuclear reactions, so the need for “ilem” seemed to disappear.
Clarification chemical composition Space soon led to controversy. If we calculate how much hydrogen in the stars of our Galaxy should have “burned out” into helium during its existence (10 billion years), it turns out that the observed amount of helium is 20 times greater than that obtained according to theoretical calculations. This means that the source of helium formation should be not only its synthesis in the depths of stars, but also some other, very powerful processes. In the end, we had to turn again to the idea of the Big Bang and look for a source of excess helium in it. This time success fell to the share of famous Soviet scientists Academician Ya. B. Zeldovich and I. D. Novikov, who in a series of detailed works substantiated in detail the theory of the Big Bang and the expanding Universe ( Ya. V. Zeldovich, I. D. Novikov. Structure and evolution of the Universe. M., Nauka, 1975). The main provisions of this theory are as follows.
The expansion of the Universe began with very high density and very high temperature. At the dawn of its existence, the Universe resembled a laboratory of high energies and high temperatures. But this, of course, was a laboratory that had no earthly analogies.
The very “beginning” of the Universe, i.e. its state, corresponding, according to theoretical calculations, to a radius close to zero, so far eludes even theoretical representation. The fact is that the equations of relativistic astrophysics remain valid up to a density of the order of 10 93 g/cm3. The Universe, compressed to such a density, once had a radius of about one ten-billionth of a centimeter, i.e. it was comparable in size to a proton! The temperature of this microuniverse, which, by the way, weighed no less than 10 51 tons, was incredibly high and, apparently, close to 10 32 degrees. This is how the Universe looked like an insignificant fraction of a second after the start of the “explosion”. At the “beginning” itself, both density and temperature turn to infinity, i.e. this “beginning,” using mathematical terminology, is that special “singular” point for which the equations of modern theoretical physics lose physical meaning. But this does not mean that there was nothing before the “beginning”: we simply cannot imagine What was before the conventional “beginning” of the Universe.
In our life, a second is an insignificant interval. In the very first moments of the life of the Universe (conventionally counted from the “beginning”), many events unfolded within the first second. The term "expansion" here seems too weak and therefore inappropriate. No, it was not an expansion, but a powerful explosion.
By the end of one hundred thousandth of a second after the “beginning,” the Universe in its microvolume contained a mixture elementary particles: nucleons and antinucleons, electrons and positrons, as well as mesons, light quanta (photons). In this mixture, according to Ya. B. Zeldovich, there were probably hypothetical (for now) gravitons and quarks ( Gravitons and quarks are hypothetical particles; the interaction of gravitons with other particles determines the gravitational field (these are quanta gravitational field); quarks are the “basic building blocks”, the combinations of which give rise to all the variety of particles. A lot of effort and money has been spent on detecting quarks, but they have not yet been found), but the main role still apparently belonged to neutrinos.
When the “age” of the Universe was one ten-thousandth of a second, its average density (10 14 g/cm3) was already close to the density of atomic nuclei, and the temperature dropped to approximately several billion degrees. By this time, nucleons and antinucleons had already managed to annihilate, that is, mutually destroyed, turning into quanta of hard radiation. Only the number of neutrinos produced during the interaction of particles was maintained and increased, since neutrinos interact most weakly with other particles. This growing “sea” of neutrinos isolated the longest-living particles - protons and neutrons - from each other and caused the transformation of protons and neutrons into each other and the birth of electron-positron pairs. It is unclear what causes the subsequent predominance of particles and the small number of antiparticles in our world. Perhaps for some reason there was an initial asymmetry: the number of antiparticles was always less than the number of particles, or, as some scientists believe, thanks to an as yet unknown separation mechanism, particles and antiparticles were sorted, concentrating in different parts of the Universe, and antiparticles somewhere like this they predominate (as particles predominate in our world), forming an antiworld.
According to Ya. B. Zeldovich, “at the moment, in the Universe there are only quanta that we observe, as well as neutrinos and gravitons, which modern means We can’t observe and probably won’t be able to for many years.”
Let's continue the quote:
“So, over time, all particles in the Universe “die out”, only quanta remain. This is correct to within one hundred millionth. But in reality there is one proton or neutron for every hundred million quanta. These particles are preserved because they - the remaining particles - have nothing to annihilate with (at first, nucleons, protons and neutrons annihilated with their antiparticles). There are few of them, but it is from these particles, and not from quanta, that the Earth and planets, the Sun and stars consist" ( Earth and Universe, 1969, No. 3, p. 8 (Ya. B. Zeldovich. Hot Universe)).
When the age of the Universe reached a third of a second, the density dropped to 10 7 g/cm3, and the temperature dropped to 30 billion degrees. At this moment, according to Academician V.L. Ginzburg, neutrinos are separated from nucleons and are no longer absorbed by them. Today, these “primary” neutrinos traveling in outer space should have an energy of only a few ten-thousandths of an electronvolt. We do not know how to detect such neutrinos: to do this, the sensitivity of modern equipment must be increased hundreds of thousands of times. If this can ever be done, “primary” neutrinos will bring us valuable information about the first second of the life of the Universe.
By the end of the first second, the Universe had expanded to a size approximately one hundred times greater than the size of the modern Solar System, whose diameter is 15 billion km. Now the density of its substance is 1 t/cm3, and the temperature is about 10 billion degrees. Nothing here resembles modern space yet. There are no atoms and atomic nuclei familiar to us, and there are no stable elementary particles.
Just 0.9 seconds earlier, at a temperature of 100 billion degrees, there were equal numbers of protons and neutrons. But as the temperature decreased, the heavier neutrons decayed into protons, electrons and neutrinos. This means that the number of protons in the Universe has steadily increased, and the number of neutrons has decreased.
The age of the Universe is three and a half minutes. Theoretical calculations fix the temperature at this moment at 1 billion degrees and the density is already a hundred times less than the density of water. The size of the Universe in just three and a half minutes increased from almost zero to 40 sv. years ( For the expansion of space, the speed of light is not the limit). Conditions were created under which protons and neutrons began to combine into the nuclei of the lightest elements, mainly hydrogen. Some stabilization occurs, and by the end of the fourth minute from the beginning of the “first explosion,” the Universe consisted of 70% hydrogen and 30% helium by mass. This was probably the original composition of the most ancient stars. Heavier elements arose later as a result of the processes that occur in stars.
The further history of the Universe is calmer than its turbulent beginning. The rate of expansion gradually slowed down, the temperature, like the average density, gradually decreased, and when the Universe was a million years old, its temperature became so low (3500 degrees Kelvin) that protons and nuclei of helium atoms could already capture free electrons and turn into neutral atoms. From this moment, the modern stage of the evolution of the Universe essentially begins. Galaxies, stars, planets appear. Eventually, after many billions of years, the Universe became the way we see it.
Perhaps some of the readers, amazed by the colossal numbers, far from the usual reality, will think that drawn in the most general outline The history of the Universe is only a theoretical abstraction, far from reality. But that's not true. The expanding universe theory explains the recession of galaxies. It is confirmed by many modern data about space. Finally, another very convincing experimental confirmation of the super-hot state of the ancient Universe was recently found.
The primary plasma that initially filled the Universe consisted of elementary particles and radiation quanta, or photons - it was the so-called photon gas. Initially, the radiation density in the “microuniverse” was very high, but as it expanded, the “photon gas” gradually cooled. This would cool the hot air inside some continuously expanding closed volume.
Nowadays, only subtle traces should remain of the primary “heat”. The energy of the quanta of the primary “photon gas” has decreased to a value corresponding to a temperature just a few degrees above absolute zero. Nowadays, the primary “photon gas” should emit most intensely in the centimeter radio range.
These are the theoretical predictions. But they are confirmed by observations. In 1965, American radio physicists discovered noise radio emission at a wave of 7.3 cm. This emission came uniformly from all points in the sky and was clearly not associated with any discrete cosmic radio source. Neither earthly radio stations nor interference generated by radio equipment are to blame.
Thus, the cosmic microwave background radiation of the Universe was discovered, a remnant of its original unimaginably high temperature. Thus, the “hot” model of the primary Universe, theoretically calculated by Ya. B. Zeldovich and his students, was confirmed.
So, apparently, the Universe was born as a result of a powerful “first explosion”. From an insignificantly small volume, but super-heavy, super-dense, super-hot clot of matter and radiation, over the course of several billion years, what we now call Space arose.
When the Universe expanded from a very small but unimaginably dense clump of matter to cosmic dimensions, its gigantic, still very hot and super-dense ball probably disintegrated into many “fragments.” This could be a consequence, for example, of the heterogeneity of the ball and the different rates of processes occurring in it.
Each of the “fragments,” consisting of prestellar matter with enormous reserves of energy, in turn disintegrated over time. It is possible that the decay products were quasars - the embryos of galaxies. As Academician V.A. Ambartsumyan and other researchers believe, the cores of quasars (as well as the cores of galaxies) contain prestellar matter, the properties of which we cannot yet determine, and their outer layers consist of plasma and gases, the density of which is only several times higher than the density of matter in galaxies. If this is so, then we must admit that the “first explosion” and subsequent secondary explosions ejected into space not only “fragments” of prestellar matter, but also diffuse matter - plasma, gases from which dust material was formed. At the same time, one must think that the initial content of gas and dust matter in the Universe was significantly higher than it is now.
Be that as it may, according to us modern ideas, up to the stage of the appearance of galaxies in the Universe, explosive processes prevailed. But as we have seen, explosive processes are also characteristic of the stage of galaxies, although their intensity decreases in the process of galaxy evolution - from violent manifestations of energy in the Markarian and Seyfert galaxies to the calm outflow of matter from the cores of galaxies such as ours. Thus, the theory of the expanding Universe may be compatible with the concept of Academician Ambartsumyan, who, based on his own discoveries and the discoveries of his collaborators, as well as on the works of foreign astronomers, extends the idea of a creative explosion to star formation processes. According to this concept, all cosmic objects known to us (galaxies, stars, gas-dust nebulae) are born in the process of an explosion from super-dense clumps of prestellar matter filled with huge reserves of energy. That is why stars appear in the form of an expanding, initially compact group consisting of many thousands or millions of stars. This hypothesis seems to the author the most probable of all others, and therefore he proposes the following “pedigree” of all space objects.
The “Primary Atom,” i.e., the Universe in the primary superdense state, and the primary fireball are its most distant ancestors, which, of course, gave, in addition to the planets, almost countless offspring of all cosmic objects.
Some fragment of the fireball may have become the embryonic core of our Galaxy and, over time, acquired a stellar population. This embryonic galactic core and, probably, the stellar association that spun off from it, which included the Sun, are the next “relatives” of the Earth, closer to us in time.
The proposed scheme for the evolution of the cosmos from the “first atom” to the stars is only a hypothesis that is subject to further development and testing. So far, no theory of the transformation of hypothetical “pre-stellar matter” into observable space objects exists, and this circumstance is one of the weak points in V. A. Ambartsumyan’s concept.
On the other hand, the birth of stars through the condensation of rarefied gas and dust matter cannot be considered absolutely impossible; on the contrary, most astronomers still adhere to such a “condensation” hypothesis. Giant accumulations of gas and dust matter may have arisen at the stage of “secondary” explosions of “fragments of the primary explosion.” It can be assumed that the distribution of matter in them was initially uneven. Some general rotation of such clusters probably gives rise to powerful magnetic fields, due to which the structure of gas and dust clouds could become fibrous. Under influence gravitational forces It was in the extensions (nodes) of these “fibers” that the concentration of matter could begin, leading to the emergence of entire families of stars.
Most researchers still adhere to this concept, although it also has its own weak sides. It is quite possible that both concepts (“explosive” and “condensation”) do not exclude, but complement each other: after all, during the decay of prestellar matter, not only stars, but also nebulae appear. Maybe the matter of these nebulae will someday serve (or has already served many times) as the starting material for the condensation of stars and planets? Only future research will be able to bring complete clarity to this issue.
The Big Bang theory, developed by Ya. B. Zeldovich and N. D. Novikov, perfectly explained the “excess” of helium in the Universe. According to their recent calculations, already 100 seconds after the start of expansion, the Universe contained 70% hydrogen and about 30% helium. The rest of the helium and heavier elements appeared during the evolution of stars.
Despite this great success, the horizons for the Big Bang theory are by no means bleak. Behind Lately A number of facts have been discovered that do not fit into the framework of this theory ( For more details, see the book: V. P. Chechev, Ya. M. Kramarovsky. Radioactivity and the evolution of the universe. M., Nauka, 1978). For example, galaxies are known that are clearly physically connected with each other and are located at equal distance, but having significantly different (sometimes 13 times!) “redshifts”. Another thing that is unclear is why, at the same distance, spiral galaxies always have larger “redshifts” than elliptical galaxies. According to some data, it turns out that in different directions the rate of expansion, “swelling” of the Universe is not the same, which contradicts the previously prevailing ideas about the strictly “spherical” shape of the expanding world?
Finally, it was recently discovered that the velocities of galaxies relative to the background cosmic microwave background radiation very small. They are measured not in thousands and tens of thousands of kilometers per second, as follows from the theory of the expanding Universe, but only in hundreds of kilometers per second. It turns out that the galaxies are practically at rest relative to the relict background of the Universe, which for a number of reasons can be considered an absolute frame of reference ( For more details, see the book: Development of methods of astronomical research (A. A. Efimov. Astronomy and the principle of relativity). M., Nauka, 1979, p. 545).
How to overcome these difficulties is still unclear. If it turns out that the “red shift” in the spectra of galaxies is caused not by the Doppler effect, but by some other process not yet known to us, the drawn diagram of the origin of chemical elements may turn out to be incorrect. However, most likely Big Bang not an illusion, but a reality, and the theory of a “hot” expanding Universe is one of the most important achievements of science of the 20th century.
In conclusion, we note that no matter what views on the evolution of the Universe one adheres to, the indisputable fact remains unshakable - we live in a chemically unstable World, the composition of which is constantly changing.
About 4.5 billion years have passed since the origin of our planet. Now only those elements have been preserved on Earth that did not decay during this time, that is, they were able to “survive” to this day - in other words, their half-life is longer than the age of the Earth. We can see the names of these elements in the Periodic Table of Elements (up to uranium).
All elements heavier than uranium were once formed in the process of nuclear fusion, but did not survive to this day. Because they have already broken up.
That's why people are forced to reproduce them again.
For example: Plutonium. Its half-life is only 25 thousand years - very little compared to the life of the Earth. This element, experts say, certainly existed at the birth of the planet, but has already decayed. Plutonium is produced artificially in tens of tons and is known to be one of the most powerful sources of energy.
What is the process of artificial synthesis?
Scientists are not able to recreate the situation of the conditional “creation of the world” (i.e., the necessary state of matter at temperatures of billions of degrees Celsius) in laboratory conditions. It is impossible to “create” the elements exactly as they did during the formation of the Solar System and the Earth. In the process of artificial synthesis, specialists act by means available here on Earth, but receive general idea about how this could happen then and how it may be happening now on distant stars.
In general terms, the experiment proceeds as follows. To the core natural element(for example, calcium) neutrons are added until the nucleus stops accepting them. The last isotope, overloaded with neutrons, does not last long, and the next one cannot be produced at all. This is the critical point: the limit of the existence of nuclei overloaded with neutrons.
How many new elements can be created?
Unknown. Border question Periodic table is still open.
Who comes up with the names for the new elements?
The procedure for recognizing a new element itself is very complex. One of the key requirements is that the discovery must be independently cross-checked and experimentally confirmed. This means that it must be repeated.
For example, it took 14 years for the official recognition of the 112th element, which was obtained in Germany in 1996. The element’s “baptism” ceremony took place only in July 2010.
There are several in the world the most famous laboratories, whose employees managed to synthesize one or even several new elements. These are the Joint Institute for Nuclear Research in Dubna (Moscow region), Livermore National Laboratory. Lawrence in California (USA), National Laboratory. Lawrence Berkeley (USA), European Center for the Study of Heavy Ions. Helmholtz in Darmstadt (Germany), etc.
After the International Union of Pure and Applied Chemistry (IUPAC) recognizes the synthesis of new chemical elements, the right to propose names for them they are received by officially recognized discoverers.
The preparation used materials from articles and interviews with Academician Yuri Oganesyan, scientific director of the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna.
, plutonium), in the photospheres of stars (technetium and, possibly, promethium), in the shells of supernovae (californium and, probably, its decay products - berkelium, curium, americium and lighter ones).
The last element found in nature before it was synthesized artificially was francium (1939). The first chemical element synthesized was technetium in 1937. As of 2012, elements up to ununoctium with atomic number 118 have been synthesized by nuclear fusion or fission, and attempts have been made to synthesize the following superheavy transuranium elements. The synthesis of new transactinoids and superactinoids continues.
The most famous laboratories that have synthesized several new elements and several tens or hundreds of new isotopes are the National Laboratory named after. Lawrence in Berkeley and Livermore National Laboratory (USA), in Dubna (USSR / Russia), European (Germany), Cavendish Laboratory of Cambridge University (UK), (Japan) and others. In recent decades, the synthesis of elements in American, German and Russian centers International teams work.
Discovery of synthesized elements by country
USSR, Russia
USA
Germany
Contested priorities and joint results
For a number of elements, the priority is equally approved according to the decision of the joint commission of IUPAC and IUPAP or remains controversial:
USA and Italy
Russia and Germany
Russia and Japan
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- About the synthesis of elements on the website “Atomic and space industry Russia", ,
- About the synthesis of elements on the website “Virtual Periodic Table”,
- About the synthesis of elements on the site, ,
An excerpt characterizing Synthesized Chemical Elements
– What are we going to do with them? – Stella sighed convulsively and pointed to the kids huddled together. - There is no way to leave here.I didn’t have time to answer when a calm and very sad voice sounded:
“I’ll stay with them, if you allow me, of course.”
We jumped up together and turned around - it was the man Mary saved who spoke... And somehow we completely forgot about him.
- How are you feeling? – I asked as friendly as possible.
I honestly did not wish harm to this unfortunate stranger, saved at such a high price. It wasn't his fault, and Stella and I understood that very well. But the terrible bitterness of loss was still clouding my eyes with anger, and although I knew that this was very, very unfair for him, I just couldn’t pull myself together and push this terrible pain out of myself, leaving it “for later” when I completely alone, and, having locked myself “in my corner,” I could give vent to bitter and very heavy tears... And I was also very afraid that the stranger would somehow feel my “rejection,” and thus his liberation would lose its importance and beauty victory over evil, in the name of which my friends died... Therefore, I tried my best to pull myself together and, smiling as sincerely as possible, waited for the answer to my question.
The man sadly looked around, apparently not quite understanding what had happened here, and what had been happening to himself all this time...
“Well, where am I?” he asked quietly, his voice hoarse from excitement. -What kind of place is this, so terrible? It's not like what I remember... Who are you?
- We are friends. And you’re absolutely right - this is not a very pleasant place... And a little further on, the places are generally wildly scary. Our friend lived here, he died...
- I'm sorry, little ones. How did your friend die?
“You killed him,” Stella whispered sadly.
I froze, staring at my friend... This was not said by the “sunny” Stella, whom I knew well, who “without fail” felt sorry for everyone, and would never make anyone suffer!.. But, apparently, the pain of loss, like me, it gave her an unconscious feeling of anger “at everyone and everything,” and the baby was not yet able to control this within herself.
“Me?!..” the stranger exclaimed. – But this cannot be true! I've never killed anyone!..
We felt that he was telling the absolute truth, and we knew that we had no right to shift the blame of others onto him. Therefore, without even saying a word, we smiled together and immediately tried to quickly explain what really happened here.
The man was in a state of absolute shock for a long time... Apparently, everything he heard sounded wild to him, and certainly did not coincide with what he really was, and how he felt about such terrible evil, which does not fit into normal human frameworks ...
- How can I make up for all this?!.. After all, I can’t? And how can we live with this?!.. - he grabbed his head... - How many have I killed, tell me!.. Can anyone say this? What about your friends? Why did they do this? But why?!!!..
– So that you can live as you should... As you wanted... And not as someone wanted... To kill the Evil that killed others. That’s probably why...” Stella said sadly.
- Forgive me, dear... Forgive me... If you can... - the man looked completely killed, and I was suddenly “pricked” by a very bad feeling...
- Well, I do not! – I exclaimed indignantly. - Now you must live! Do you want to nullify their entire sacrifice?! Don't even dare think! Now you will do good instead of them! It will be right. And “leaving” is the easiest thing. And now you no longer have such a right.
The stranger stared at me in amazement, apparently not expecting such a violent outburst of “righteous” indignation. And then he smiled sadly and said quietly:
- How you loved them!.. Who are you, girl?
My throat became very sore and for some time I could not squeeze out a word. It was very painful because of such a heavy loss, and, at the same time, I was sad for this “restless” person, for whom it would be oh, how difficult it would be to exist with such a burden...
- I am Svetlana. And this is Stella. We're just hanging out here. We visit friends or help someone when we can. True, there are no friends left now...
- Forgive me, Svetlana. Although it probably won’t change anything if I ask you for forgiveness every time... What happened happened, and I can’t change anything. But I can change what will happen, right? - the man glared at me with his eyes blue as the sky and, smiling, a sad smile, said: - And yet... You say I am free in my choice?.. But it turns out - not so free, dear... It looks more like atonement... Which I agree with, of course. But it is your choice that I am obliged to live for your friends. Because they gave their lives for me... But I didn’t ask for this, right?.. Therefore, it’s not my choice...