Radioactive chemical element. Artificial radioactive element
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?
Alexey Levin
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, 92 elements were thought to exist 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 the 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 first 94 elements, 83 have either stable or long-lived isotopes whose half-lives are comparable to age 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 arise in the earth’s crust only as a result of radioactive decays 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.
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, although 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.
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 synthesized neptunium-239 in 1940, working on Fermi’s idea: the capture of slow neutrons by uranium-238 and the subsequent beta decay of uranium-239.
The next, element 94, plutonium, was first discovered when studying the beta decay of neptunium-238, obtained by deuteron bombardment of uranium at the University of California, Berkeley cyclotron 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 publication for almost six years 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 of 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 University of California's 60-inch cyclotron was the site of the creation of three more elements, 97, 98 and 101. The first two were named after their place of birth - Berkeley and California. Berkeley was synthesized in December 1949 by bombarding an americium target with alpha particles; californium was synthesized 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 from element number 100 - fermium - were required, 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 (they are called heavy ions), to bombard targets. 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 since the end of 1975 at the German Helmholtz Center for Heavy Ion Research in Wickhausen, one of the districts of Darmstadt.
During the bombardment of targets made of lead, bismuth, uranium or transuranes with heavy ions, highly excited (hot) nuclei appear, which 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 made 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. The total number of calcium “bullets” was 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 that could 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 of 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, it would have been possible to judge their chemical properties.”
“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.” In the photo: when a heavy ion hits the region of the target’s nuclear forces, a compound nucleus in an excited state can form. It either decays into fragments of approximately equal mass, or emits (evaporates) several neutrons and passes into the ground (unexcited) state.
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.
Compared to the ununoctium, the ununoctium 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.
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. In a short period of time - less than 40 years - the list of known chemical elements has 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 artificial fusion purposes. 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?
By studying the properties of atomic nuclei, physicists came to the conclusion that stable isotopes cannot exist for elements with atomic numbers 43, 61, 85 and 87. 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 there should be 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. The lightest element, hydrogen, has one positive charge. 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. 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 correspond exactly to the 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 its negative charge, shifts one cell to the right in the periodic system, and its serial number becomes one more - a transformation of elements occurs. Thus, under the influence of neutrons, heavier elements are usually formed.
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 the unimaginably complex mixture of 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) disintegrates into the atomic nuclei of bromine (35) and lanthanum (57); the fragments of the splitting of another 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 the mastery of the person inside atomic energy.
Among the huge variety of products that arise when uranium nuclei are irradiated with neutrons, the first true transuranium element No. 93, which had remained unnoticed for a long time, was subsequently discovered. It arose when neutrons acted 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 system of Mendeleev, it follows neptunium in order, similar to the “last planet of the Solar* system, Pluto, whose orbit lies behind 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” was collected at the explosion site - soil altered by the explosion and rock. 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 find out 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 by 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 laid the foundation for a completely new scientific discipline - the physical chemistry of single atoms.
The symbol of element No. 102 No - in the periodic table is placed in brackets. And within these brackets lies the long and complex history of 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 an amazing thing turned out: 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 for 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 (i.e., 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're 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 causes less damage to the glass surface and is 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 under the microscope. From their positions, the half-life was calculated. It turned out 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 element 104 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."
Position of hydrogen in the periodic table
Hydrogen – the most common chemical element, and it is also the lightest. Its serial number is 1. In the periodic table it is in the first period. Taking into account its properties, it is placed in both 1A and 7A groups. The question arises - why?
The hydrogen nucleus consists of one proton, around which one electron rotates. Electronic formula 1 s 1 . A hydrogen molecule consists of two atoms connected by a covalent nonpolar bond. H 2 is the lightest gas. It is colorless and odorless.
Hydrogen is a chemically active substance. He can act as reducing agent and oxidizing agent.
1) with some metals it forms hydrides
2Na+H 2 =2NaH, here hydrogen is an oxidizing agent
H
0
+ 1
e
-
→
H
-1
A similar process occurs during the interaction of halogens - non-metals of group 7A
2Na+Cl2 =2NaCl
Therefore, hydrogen is placed in group 7A
2) with non-metals exhibiting stronger oxidizing properties than hydrogen
H 2 +Cl 2 =2HCl here hydrogen is a reducing agent
H
0
- 1
e
-
→
H
+1
A similar process occurs during the interaction of alkali metals – group 1A metals
2K+ Cl 2 =2K Cl
Therefore, hydrogen is placed in group 1A
Position of lanthanides and actinides in the periodic table of chemical elements by D.I. Mendeleev
IN sixth period following lanthanum there are 14 elements with serial numbers 58-71, called lanthanides (the word “lanthanides” means “like lanthanum”, and “actinides” means “like actinium”). They are sometimes called lanthanides and actinides, meaning those following lanthanum; following sea anemone) . Lanthanides are placed separately at the bottom of the table, and the asterisk in the cell indicates the sequence of their location in the system: La-Lu. The chemical properties of lanthanides are very similar. For example, they are all reactive metals, reacting with water to form hydroxide and hydrogen. In lanthanum (Z = 57), one electron enters the 5d sublevel, after which the filling of this sublevel stops, and the 4f level begins to be filled, the seven orbitals of which can be occupied by 14 electrons. This occurs in atoms of all lanthanides with Z = 58 - 71. Since the deep 4f sublevel is filled in these elements third level outside, they have very similar chemical properties.
It follows from this that lanthanides have a strongly pronounced horizontal analogy.
IN seventh period 14 elements with serial numbers 90-103 make up the family actinides. They are also placed separately - under the lanthanides, and in the corresponding cell two asterisks indicate the sequence of their location in the system: Ac-Lr. In actinium and actinides, the filling of levels with electrons is similar to lanthanum and lanthanides. However, unlike the lanthanides, the horizontal analogy in the actinides is weakly expressed. They exhibit more different oxidation states in their compounds. For example, the oxidation state of actinium is +3, and uranium is +3, +4, +5 and +6. Studying the chemical properties of actinides is extremely difficult due to the instability of their nuclei.
All actinides are radioactive. Actinides are divided into two overlapping groups: "transuranic elements"- all the elements following uranium in the periodic table and "transplutonium elements"- all following plutonium. Both groups are not limited to the specified framework and, when indicating the prefix “trans-”, can include elements following lawrencium - rutherfordium, etc. This is due to the fact that such elements are synthesized in extremely small quantities. Compared to lanthanides, which (except promethium) are found in nature in noticeable quantities, actinides are more difficult to synthesize. But there are exceptions, for example, uranium and thorium are the easiest to synthesize or find in nature, followed by plutonium, americium, actinium, protactinium and neptunium.
Position in the periodic table of chemical elements by D. I. Mendeleev of artificially obtained elements
By 2008, 117 chemical elements were known (with serial numbers from 1 to 116 and 118), of which 94 were found in nature (some only in trace quantities), the remaining 23 were obtained artificially as a result of nuclear reactions (see Appendices). The first 112 elements have permanent names, the rest have temporary names.
Technetium
TECHNETIUM-I; m.[from Greek technetos - artificial] Chemical element (Tc), a silver-gray radioactive metal obtained from nuclear waste.
◁ Technetium, oh, oh.
technetium(lat. Technetium), a chemical element of group VII of the periodic table. Radioactive, the most stable isotopes are 97 Tc and 99 Tc (half-life, respectively, 2.6 10 6 and 2.12 10 5 years). The first artificially produced element; synthesized by Italian scientists E. Segre and C. Perriez in 1937 by bombarding molybdenum nuclei with deuterons. Named from the Greek technētós - artificial. Silver gray metal; density 11.487 g/cm3, t pl 2200°C. Found in nature in small quantities in uranium ores. Spectrally detected on the Sun and some stars. Obtained from waste from the nuclear industry. Component of catalysts. Isotope 99 m Tc is used in the diagnosis of brain tumors and in studies of central and peripheral hemodynamics.
TECHNETIUMTECHNETIUM (Latin Technetium, from Greek technetos - artificial), Tc (read “technetium”), the first artificially produced radioactive chemical element, atomic number 43. It has no stable isotopes. The longest-lived radioisotopes: 97 Tc (T 1/2 2.6 10 6 years, electron capture), 98 Tc (T 1/2 1.5 10 6 years) and 99 Tc (T 1/2 2.12 10 5 years). The short-lived nuclear isomer 99m Tc (T 1/2 6.02 hours) is of practical importance.
The configuration of the two outer electronic layers is 4s 2 p 6 d 5 5s 2. Oxidation states from -1 to +7 (valency I-VII); most stable +7. Located in group VIIB in the 5th period of the periodic table of elements. The radius of the atom is 0.136 nm, the Tc 2+ ion is 0.095 nm, the Tc 4+ ion is 0.070 nm, and the Tc 7+ ion is 0.056 nm. Successive ionization energies are 7.28, 15.26, 29.54 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,9.
D. I. Mendeleev (cm. MENDELEEV Dmitry Ivanovich) when creating the periodic table, he left an empty cell in the table for technetium, a heavy analogue of manganese (“ecamanganese”). Technetium was obtained in 1937 by C. Perrier and E. Segre by bombarding a molybdenum plate with deuterons (cm. DEUTRON). In nature, technetium is found in negligible quantities in uranium ores, 5·10 -10 g per 1 kg of uranium. Spectral lines of technetium have been found in the spectra of the Sun and other stars.
Technetium is isolated from a mixture of fission products 235 U - waste from the nuclear industry. When reprocessing spent nuclear fuel, technetium is extracted using ion exchange, extraction, and fractional precipitation methods. Technetium metal is obtained by reducing its oxides with hydrogen at 500°C. World production of technetium reaches several tons per year. For research purposes, short-lived radionuclides of technetium are used: 95m Tc( T 1/2 =61 days), 97m Tc (T 1/2 =90 days), 99m Tc.
Technetium is a silver-gray metal, with a hexagonal lattice, A=0.2737 nm, c= 0.4391 nm. Melting point 2200°C, boiling point 4600°C, density 11.487 kg/dm3. The chemical properties of technetium are similar to rhenium. Standard electrode potential values: Tc(VI)/Tc(IV) pair 0.83 V, Tc(VII)/Tc(VI) pair 0.65 V, Tc(VII)/Tc(IV) pair 0.738 V.
When burning Tc in oxygen (cm. OXYGEN) yellow higher acidic oxide Tc 2 O 7 is formed. Its solution in water is technetic acid HTcO 4. When it evaporates, dark brown crystals form. Salts of technical acid - pertechnates (sodium pertechnate NaTcO 4, potassium pertechnate KTcO 4, silver pertechnate AgTcO 4). During the electrolysis of a solution of technical acid, TcO 2 dioxide is released, which, when heated in oxygen, turns into Tc 2 O 7.
Interacting with fluorine, (cm. FLUORINE) Tc forms golden-yellow crystals of technetium hexafluoride TcF 6 when mixed with TcF 5 pentafluoride. Technetium oxyfluorides TcOF 4 and TcO 3 F were obtained. Chlorination of technetium gives a mixture of TcCl 6 hexachloride and TcCl 4 tetrachloride. Technetium oxychlorides TcO 3 Cl and TcOCl 3 were synthesized. Known sulfides (cm. SULFIDES) technetium Tc 2 S 7 and TcS 2, carbonyl Tc 2 (CO) 10. Tc reacts with nitrogen, (cm. NITRIC ACID) concentrated sulfur (cm. SULFURIC ACID) acids and aqua regia (cm. AQUA REGIA). Pertechnates are used as corrosion inhibitors for mild steel. Isotope 99 m Tc is used in the diagnosis of brain tumors, in the study of central and peripheral hemodynamics (cm. HEMODYNAMICS).
encyclopedic Dictionary . 2009 .
Synonyms:See what “technetium” is in other dictionaries:
Nuclide table General information Name, symbol Technetium 99, 99Tc Neutrons 56 Protons 43 Properties of the nuclide Atomic mass 98.9062547(21) ... Wikipedia
- (symbol Tc), silver-gray metal, RADIOACTIVE ELEMENT. It was first obtained in 1937 by bombarding MOLYBDENUM nuclei with deuterons (the nuclei of DEUTERium atoms) and was the first element synthesized in a cyclotron. Technetium found in products... ... Scientific and technical encyclopedic dictionary
TECHNETIUM- artificially synthesized radioactive chemical. element, symbol Tc (lat. Technetium), at. n. 43, at. m. 98.91. T. is obtained in fairly large quantities from the fission of uranium 235 in nuclear reactors; managed to obtain about 20 isotopes of T. One of... ... Big Polytechnic Encyclopedia
- (Technetium), Tc, artificial radioactive element of group VII of the periodic table, atomic number 43; metal. Obtained by Italian scientists C. Perrier and E. Segre in 1937 ... Modern encyclopedia
- (lat. Technetium) Tc, chemical element of group VII of the periodic system, atomic number 43, atomic mass 98.9072. Radioactive, the most stable isotopes are 97Tc and 99Tc (half-lives are 2.6.106 and 2.12.105 years, respectively). First… … Big Encyclopedic Dictionary
- (lat. Technetium), Tc radioact. chem. element of group VII is periodic. Mendeleev's system of elements, at. number 43, the first of the artificially obtained chemicals. elements. Naib. long-lived radionuclides 98Tc (T1/2 = 4.2·106 years) and available in noticeable amounts... ... Physical encyclopedia
Noun, number of synonyms: 3 metal (86) ecamanganese (1) element (159) Dictionary of synonyms ... Synonym dictionary
Technetium- (Technetium), Tc, artificial radioactive element of group VII of the periodic table, atomic number 43; metal. Obtained by Italian scientists C. Perrier and E. Segre in 1937. ... Illustrated Encyclopedic Dictionary
43 Molybdenum ← Technetium → Ruthenium ... Wikipedia
- (lat. Technetium) Te, radioactive chemical element of group VII of the periodic system of Mendeleev, atomic number 43, atomic mass 98, 9062; metal, malleable and ductile. The existence of element with atomic number 43 was... ... Great Soviet Encyclopedia
Books
- Elements. A wonderful dream of Professor Mendeleev, Kuramshin Arkady Iskanderovich, What chemical element is named after goblins? How many times has technetium been “discovered”? What are "transfer wars"? Why did even pundits once confuse manganese with magnesium and lead with... Category: Chemical Sciences Series: Scientific Pop of Runet Publisher: AST,
- Elements: a wonderful dream of Professor Mendeleev, Kuramshin A., Which chemical element is named after goblins? How many times has technetium been “discovered”? What are "transfer wars"? Why did even pundits once confuse manganese with magnesium and lead with... Category: